Download Abstracts - QCMC 2016 - Centre for Quantum Technologies

Abstracts
Scientific Programme
Monday (4 July)
08:30 Registration
09:00 Carl Caves, University of New Mexico
Two Studies in Interferometry: Practical Metrology and
Imperfect Boson Sampling
09:30 Klaus Molmer, University of Aarhus, Denmark
Quantum trajectories and past quantum states
10:00 Mete Atature, University of Cambridge
Entangling independent quantum-dot spins
10:30 Coffee/Tea Break
11:00 Alessandro Cere, Centre for Quantum Technologies, NUS
Time-resolved Scattering of a Single Photon by a Single Atom
11:20 Leonid Krivitsky, Data Storage Institute
Infrared Spectroscopy with Visible Light
11:40 Florian Kaiser, Université Nice Sophia Antipolis
Spectrally resolved white-light quantum interferometry for highaccuracy chromatic dispersion measurements
12:00 Paul Kwiat, University of Illinois at Urbana-Champaign
Applications of HyperEntanglement
12:30 Lunch
14:00 Matthew Pusey, Perimeter Institute for Theoretical Physics
Direct experimental reconstruction of the Bloch sphere
14:30 Katharina Schwaiger, University of Innsbruck
Operational multipartite entanglement measures
15:00 Magdalena Zych, University of Queensland
Entanglement of temporal order from quantum theory and
gravity
15:30 Coffee/Tea Break
16:00 Michael Hall, Griffith University
A Many-Interacting-Worlds Approach To Quantum Mechanics
16:30 Howard Wiseman, Griffith University
Experimental Nonlocal and Surreal Bohmian Trajectories
17:30 Poster Session 1
1
Tuesday (5 July)
08:30 Registration
09:00 Andrew Doherty, University of Sydney
Quantum dot quantum computing
09:30 Michelle Simmons, University of New South Wales
Quantum Computing in Silicon with Donors
10:00 Paola Cappellaro, Massachusetts Institute of Technology
Coherent feedback of a single qubit in diamond
10:30 Coffee/Tea Break
11:00 Anirudh Narla, Department of Applied Physics, Yale
University
Concurrent Remote Entanglement of Transmon Qubits using
Flying Photons
11:20 Sen Yang, 3. Physikalisches Institut, Uni Stuttgart
High fidelity transfer and storage of photon states in a single
nuclear spin
11:40 Bill Munro, NTT Basic Research Laboratories
Quantum State Engineering using Hybridization
12:00 Adam Kaufman, Harvard University
Title to be advised
12:30 Lunch
14:00 Steve Flammia, The University of Sydney
Comparing Experiments to the Fault-Tolerance Threshold
14:30 Qiang Zhang, University of Science and Technology of
China, Shanghai
Recent experimental progress in quantum communication
15:00 Elham Kashefi, University of Edinburgh
Secure Multi-party Computing (From Classical to Quantum From Linearity to Nonlinearity)
15:30 Coffee/Tea Break
16:00 Patrick Coles, University of Waterloo
Unstructured quantum key distribution
16:20 Paolo Villoresi, Università degli Studi di Padova
Experimental Quantum Communications in Space exploiting
temporal and polarization degrees of freedom
16:40 Daniel Oblak, University of Calgary
Quantum teleportation over deployed fibres and applications to
quantum networks
17:00 Yi-Cong Zheng, Centre of Quantum Technologies, NUS
Fault-tolerant Holonomic Quantum Computation in Surface
Codes
17:30 Poster Session 2
2
Wednesday (6 July)
08:30 Registration
09:00 Ronald Hanson, Delft University of Technology
From the first loophole-free Bell test to a quantum Internet
09:30 Marissa Giustina, University of Vienna
Significant-loophole-free test of local realism with entangled
photons
10:00 Krister Shalm, NIST
A strong loophole-free test of Local Realism
10:30 Coffee/Tea Break
11:00 Harald Weinfurter, University of Munich
Event-ready loophole free Bell test using heralded atom-atom
entanglement
11:20 Roman Schmied, University of Basel
Bell correlations in a Bose-Einstein condensate
11:50 Yvonne Gao, Yale University
A Schrodinger Cat Living in Two Boxes
12:10 Hanna Le Jeannic, Laboratoire Kastler Brossel
Large-amplitude squeezed optical Schrödinger cat states with
minimized non-Gaussian operational cost
12:30 Lunch
14:00 Alex Bocharov, Microsoft
Qomputer Science at Microsoft Research
14:30 Julian Kelly, Google
Industrializing qubits through automation
15:00 Coffee/Tea Break
15:30 Bill Munro, NTT
Quantum @ NTT
16:00 Colin William, Dwave
D-Wave's Approach to Quantum Computing: 1000-qubits and
Counting!
17:00 Visit to CQT
3
Thursday (7 July)
08:30 Registration
09:00 Yasunobu Nakamura, University of Tokyo
Hybrid quantum systems using magnons in a ferromagnetic
crystal
09:30 Hugues De Riedmatten, ICFO-The Institute of Photonic
Sciences
Quantum Correlation between photons and single spin-waves
in a solid-state environment
10:00 Sungkun Hong, University of Vienna
Towards a photon-phonon quantum interface
10:30 Coffee/Tea Break
11:00 Michael Vanner, University of Oxford
Generation of Mechanical Interference Fringes by Multi-Photon
Quantum Measurement
11:20 Neil Corzo, Laboratoire Kastler Brossel
Combining 1D Nanoscale Waveguides and Cold Atoms
11:50 Michal Oszmaniec, ICFO (Barcelona)
Random symmetric states for robust quantum metrology
12:10 Jörg Schmiedmayer, TU-Wien
Determining the essential components of a quantum manybody system from experiment
12:30 Lunch
14:00 Tim Ralph, University of Queensland
Undoing the effect of loss on entanglement
14:20 Jianwei Wang, University of Bristol
Experimental realisation of a variational ground state solver on
a photonic chip
14:40 Stefanie Barz, University of Oxford
Distinguishability in three-photon scattering
15:00 Sara Ducci, Paris Diderot University
AlGaAs photonic devices: from quantum state generation to
quantum communications
15:30 Maciej Lewenstein, ICFO
Separability Revisited
Free afternoon
19:30 Conference Dinner @ Keppel Club
4
Friday (8 July)
09:00 Registration
09:30 Rainer Blatt, Universtität Innsbruck
Quantum Information Processing with Trapped Ions and
Photons
10:30 Coffee/Tea Break
11:00 Arno Rauschenbeutel, Vienna University of Technology
Programmable integrated optical circulator controlled by a
single spin-polarized atom
11:30 Chao-Yang Lu, University of Science and Technology of
China, Hefei
Creating perfect single photons for the demonstration of
quantum supremacy
12:00 David DiVincenzo, RWTH Aachen University
Longitudinal Coupling: Key to Scalable Qubit Layouts?
12:30 Closing
5
Poster List
The poster sessions will take place on 4 and 5 July (Monday and Tuesday) at 5:30pm.
There will be Poster Awards. Please use the voting card included in the Welcome Pack
to vote for your favorite poster at the end of the poster session.
Poster session I – Monday (4 July)
P1-3 - Entanglement measure for composite systems of indistinguishable particles
Janusz Grabowski
P1-4 - Heralded Measurement-Device-Independent Quantum Key Distribution with
Vector Vortex Beams
Chen Dong, Shang-Hong Zhao and Shutao Li
P1-5 - Quantum Coherence Sets The Quantum Speed Limit For Mixed States
Debasis Mondal, Chandan Datta and Sk Sazim
P1-7 - Pushing single photon counting technology towards better Size, Weight and
Power (SWAP) performance.
Rakhitha Chandrasekara, Zhongkan Tang, Yue Chuan Tan, Kadir Durak, Cliff Cheng and
Alexander Ling
P1-8 - Temporal imaging with squeezed light
Mikhail Kolobov and Giuseppe Patera
P1-10 - Quantum key distribution with leaky devices
Marcos Curty, Kiyoshi Tamaki and Marco Lucamarini.
P1-11 - Survivor! Analysis of a photon pair source recovered intact from a catastropic
launch failure.
Tang Zhongkan Xavier, Alexander Ling, Rakhitha Chandrasekara, Yue Chuan Tan and Cliff
Cheng
P1-12 - Semiclassical Theory of Superresolution for Two Incoherent Optical Point
Sources
Mankei Tsang, Ranjith Nair and Xiao-Ming Lu
P1-13 - Quantum State Smoothing
Howard Wiseman and Ivonne Guevara
P1-15 - Electronic and spin properties of Si vacancy in SiC
Moein Najafi Ivaki and Mohammad Ali Vesaghi
P1-17 - Optimal two-mode attack against two-way continuous-variable quantum key
distribution
Yichen Zhang, Zhengyu Li, Yijia Zhao, Song Yu and Hong Guo
P1-18 - Measurement-based Formulation of Quantum Heat Engine
Masahito Hayashi and Hiroyasu Tajima
6
P1-19 - Development of single photon source using Silicon-Vacancy(SiV) nanodiamond
Hong Kee Suk, Bae In-Ho and Lee Dong-Hoon
P1-21 - Inhibition of ground-state superradiance and light-matter decoupling in circuit
QED
Zeliang Xiang, Tuomas Jaako and Peter Rabl
P1-22 - Steering Bell-diagonal states
Quan Quan
P1-23 - Suppression law of quantum states in a 3D photonic fast Fourier transform
chip
Niko Viggianiello
P1-28 - Quantum dot based simultaneous classical logic gates
Ronny A. Christin and Duncan L. MacFarlane
P1-29 - Error probability in quantum-dot based quantum circuits
Ronny A. Christin and Duncan L. MacFarlane
P1-30 - Measurement-dependent locality with non-i.i.d. measurements
Ernest Y.-Z. Tan, Yu Cai and Valerio Scarani
P1-32 - Weiss-Weinstein Error Bounds for Quantum Parameter Estimation
Xiao-Ming Lu and Mankei Tsang
P1-33 - Quantum state preparation: the untold story
Holger F. Hofmann
P1-34 - Multi-photon interference explained by the action of optical phase shifts
Holger F. Hofmann, Keito Hibino, Kazuya Fujiwara and Jun-Yi Wu
P1-35 - Atoms as quantum beam-splitters in waveguide QED
Alexandre Roulet, Pierre-Olivier Guimond, Jibo Dai, Huy Nguyen Le and Valerio Scarani
P1-36 - Robust H∞ Estimation for Linear Uncertain Quantum Systems
Shibdas Roy and Ian Petersen
P1-37 - Two qubit near-field microwave gates on 43Ca+
James Tarlton, Martin Sepiol, Jochen Wolf, Thomas Harty, Christopher Ballance, Diana
Craik, Vera Schafer, Keshav Thirumalai, Laurent Stephenson, Andrew Steane and David
Lucas
P1-39 - Protecting quantum discord from amplitude damping decoherence via weak
measurement and its reversal
Yong-Su Kim, Jiwon Yune, Kang-Hee Hong, Hyang-Tag Lim, Jong-Chan Lee, Osung Kwon,
Sang-Wook Han, Sung Moon and Yoon-Ho Kim
P1-40 - Experimental demonstration of efficient superdense coding in the presence of
non-Markovian noise
Bi-Heng Liu, Xiao-Min Hu, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, Sabrina
Maniscalco and Jyrki Piilo
7
P1-41 - An analysis of the statistics of multi-photon interference
Kazuya Fujiwara and Holger F. Hofmann
P1-43 - Phase-encoded measurement device independent quantum key distribution
without a shared reference frame
Ying Sun and Shang-Hong Zhao
P1-44 - Unitary Estimation with Resource Constraints
Masahito Hayashi, Sai Vinjanampathy and Leong Chuan Kwek
P1-45 - Experimental Tests of Gravitational Decoherence
Nathan Mcmahon and Gerard Milburn
P1-46 - Time multiplexing toward indistinguishable and deterministic single-photon
generation
Fumihiro Kaneda and Paul Kwiat
P1-48 - All-­‐Semiconductor Quantum Repeater Device
Danny Kim, Andrey Kiselev, Richard Ross, Matthew Rakher, Cody Jones and Thaddeus
Ladd
P1-49 - Surface effects on the coherence of superconducting qubits
Yiwen Chu, Christopher Axline, Chen Wang, Teresa Brecht, Yvonne Gao, Luigi Frunzio,
Michel Devoret and Robert Schoelkopf
P1-50 - Optical properties of an atomic ensemble coupled to a band edge of a
photonic crystal waveguide
Ewan Munro, Leong Chuan Kwek and Darrick Chang
P1-51 - Practical Quantum Retrieval Games
Juan Miguel Arrazola, Markos Karasamanis and Norbert Lutkenhaus
P1-52 - Non-local games and optimal steering at the boundary of the quantum set
Yi-Zheng Zhen, Koon Tong Goh, Yu-Lin Zheng, Wen-Fei Cao, Xingyao Wu, Kai Chen and
Valerio Scarani
P1-53 - Multiparty Quantum Signature Schemes
Juan Miguel Arrazola, Petros Wallden and Erika Andersson
P1-54 - A scheme for estimating accidental coincidence rates between saturated
single photon detectors: the effective duty cycle
James Grieve, Rakhitha Chandrasekara, Zhongkan Tang, Cliff Cheng and Alexander Ling
P1-56 - Highly confining direct written waveguides for integrated quantum photonics
James Grieve, Bo Xue Tan and Alexander Ling
P1-57 - Engineering high brightness and high efficiency in downconversion sources
Brigitta Septriani, James Grieve, Alexander Ling and Kadir Durak
P1-58 - Multiphoton entanglement from single photon sources
Jun-Yi Wu and Holger F. Hofmann
8
P1-59 - Optical Resources and the Maxwell Demon
Angeline Shu, Jibo Dai and Valerio Scarani
P1-60 - Full reconstruction of a 14-qubit state within 4 hours
Zhibo Hou and Guo-Yong Xiang
P1-61 - Scalable quantum router architecture with code interoperability
Shota Nagayama, Shigeya Suzuki, Takahiko Satoh, Takaaki Matsuo and Rodney Van Meter
P1-62 - Entanglement of quantum circular states of light
Mikhail Kolobov, Dmitri Horoshko, Stephan De Bievre and Giuseppe Patera.
P1-66 - Wide-area topology of a Quantum Internet
Takaaki Matsuo, Takahiko Satoh, Shota Nagayama, Shigeya Suzuki and Rodney Van Meter
P1-70 - Towards storage of single quantum dot photons in a rubidium quantum
memory
Janik Wolters, Lucas Beguin, Jan-Philipp Jahn, Mathieu Munsch, Andrew Horsley, Fei Ding,
Aline Faber, Andreas Jöckel, Andreas Kuhlmann, Armando Rastelli, Oliver G. Schmidt,
Richard J. Warburton and Philipp Treutlein
P1-71 - Quantum teleportation between multiple senders and receivers
Seung-Woo Lee, Hee Su Park and Hyunseok Jeong
P1-72 - On-chip coherent conversion of photonic quantum entanglement between
different degrees of freedom
Lantian Feng, Ming Zhang, Zhaiyuan Zhou, Ming Li, Xiao Xiong, Le Yu, Baosen Shi,
Guoping Guo, Daoxin Dai, Xifeng Ren and Guangcan Guo
P1-73 - Experimental quantum fingerprinting with weak coherent states
Juan Miguel Arrazola, Feihu Xu, Keijin Wei, Wenyuan Wang, Pablo Palacios-Avila, Chen
Feng, Shihan Sajeed, Hoi-Kwong Lo and Norbert Lutkenhaus
P1-74 - SpooQySats: nanosatellites to demonstrate technologies for future quantum
communication networks
Robert Bedington, Cliff Cheng, Yue Chuan Tan, Edward Truong-Cao, Xueliang Bai and
Alexander Ling
P1-75 - Many-box locality
Yu Cai, Jean-Daniel Bancal and Valerio Scarani
P1-76 - All the self-testings of the singlet for two binary measurements
Yukun Wang, Xingyao Wu and Velario Scarani
P1-77 - BosonSampling with continuous variable measurements
Austin Lund, Saleh Rahimi-Keshari and Timothy Ralph
P1-78 - Implementation of high-performance coincidence counting unit with a lowcost field programmable gate array
Byung Kwon Park, Yong-Su Kim, Osung Kwon, Sang-Wook Han and Sung Moon
P1-79 - Quantum Noise Spectroscopy
Gerardo Paz Silva, Leigh Norris and Lorenza Viola
9
P1-80 - Continuous-mode analysis of a noiseless linear amplifier
Yi Li, Andre Carvalho and Matthew James
P1-81 - Device-independent parallel self-testing of two singlets
Xingyao Wu, Jean-Daniel Bancal, Matthew Mckague and Valerio Scarani
P1-83 - Demonstration of Quantum Permutation Algorithm with a Single Photon
Ququart
Pei Zhang
P1-84 - Experimental evaluation of quantum correlations between measurement errors
using polarization-entangled photons as probe input
Yutaro Suzuki, Masataka Iinuma, Masayuki Nakano and Holger F. Hofmann
P1-85 - Development of a readout backend for a Geiger-mode SiPM
In-Ho Bae, Dong-Hoon Lee and Seongchong Park
P1-86 - The classical-quantum divergence of complexity in the Ising spin chain
Whei Yeap Suen, Jayne Thompson, Andrew Garner, Vlatko Vedral and Mile Gu
P1-87 - Experimental evaluation of non-classical correlations by sequential quantum
measurements
Masataka Iinuma, Yutaro Suzuki, Taiki Nii, Ryuji Kinoshita and Holger F. Hofmann
P1-88 - Interferences in quantum eraser reveal geometric phases in modular and weak
values
Mirko Cormann, Mathilde Remy, Branko Kolaric and Yves Caudano
P1-89 - Coherent-state discrimination via non-heralded probabilistic amplification
Matteo Rosati, Andrea Mari and Vittorio Giovannetti
P1-90 - Entangled photon-pairs emitted from Ag/GaN photonic crystals as sources for
quantum-information processing
Dalibor Javůrek and Jan Peřina Jr.
P1-91 - Conditioned quantum dynamics in a 1D lattice system
Ralf Blattmann and Mølmer Klaus
P1-95 - Testing the limits of human vision with single photons
Rebecca Holmes, Michelle Victora, Ranxiao Frances Wang and Paul Kwiat
P1-97 - Entanglement Restoration in Amended Entanglement Breaking Channels
Álvaro Andrés Cuevas Seguel, Andrea Mari, Antonella De Pasquale, Adeline Orieux,
Marcello Massaro, Fabio Sciarrino, Vittorio Giovanetti and Paolo Mataloni
P1-98 - Proper Dimension Witnessing
Wan Cong, Yu Cai, Jean-Daniel Bancal and Valerio Scarani
P1-99 - Past of a photon inside an interferometer
Yink Loong Len, Jibo Dai, Berge Englert and Leonid Krivitsky
P1-100 - Quantum error correction in the presence of small baths
Yink Loong Len, Yicong Zheng and Hui Khoon Ng
10
P1-104 - Efficient Quantum Compression for Identically Prepared Mixed States
Yuxiang Yang, Giulio Chiribella and Daniel Ebler
P1-106 - When is simpler thermodynamically better?
Andrew Garner, Jayne Thompson, Vlatko Vedral and Mile Gu
P1-107 - Weak Value Measurements with Pulse Recycling
Courtney Krafczyk, Trent Graham, Andrew Jordan and Paul Kwiat
P1-108 - Extreme Violation of Local Realism in Quantum Hypergraph States
Mariami Gachechialdze, Costantino Budroni and Otfried Guehne
P1-110 - random numbers from vacuum fluctuations
Yicheng Shi, Brenda Chng and Christian Kurtsiefer
P1-111 - Rectification of light in the quantum regime
Jibo Dai, Alexandre Roulet, Huy Nguyen Le and Valerio Scarani
P1-112 - Generation and measurement of four-dimensional entanglement in multi-core
optical fibers
Hee Jung Lee, Sang-Kyung Choi and Hee Su Park
P1-114 - Qutrit trace invariants using Bloch matrices
Vinod Mishra
P1-117 - Entanglement verification with detection-efficiency mismatch
Yanbao Zhang and Norbert Lutkenhaus
P1-118 - Experimental Adaptive Quantum Tomography of Two-Qubit States
Stanislav Straupe, Gleb Struchalin, Konstantin Kravtsov, Igor Radchenko, Ivan Pogorelov
and Sergei Kulik
P1-122 - Single-cycle squeezing of light
Dmitri Horoshko and Mikhail Kolobov
P1-124 - Realization of a two-photon quantum gate based on cavity QED
Bastian Hacker, Stephan Welte, Stephan Ritter and Gerhard Rempe
P1-126 - Spectrum analysis with quantum dynamical systems
Shilin Ng, Shan Zheng Ang, Mankei Tsang, Wheatley Trevor, Hidehiro Yonezawa, Akira
Furusawa and Elanor Huntington
P1-127 - Heisenberg’s error-disturbance relations: a joint measurement-based
experimental test
Yuan-Yuan Zhao, Paweł Kurzyński and Guo-Yong Xiang
P1-128 - Superradiant Emission of Ultra-Bright Photon Pairs in Doppler-Broadened
Atomic Ensemble
Yoon-Seok Lee, Sang Min Lee, Heonoh Kim and Han Seb Moon
P1-129 - Geometric spin echo under zero field
Yuhei Sekiguchi, Yusuke Komura, Shota Mishima, Touta Tanaka, Naeko Niikura and Hideo
Kosaka
11
P1-130 - Heralded quantum steering with no detection loophole over a high-loss
quantum channel
Geoff Pryde, Morgan Weston, Sergei Slussarenko, Sabine Wollmann and Helen
Chrzanowski
P1-131 - Entanglement degradation by macrorealistic modifications
Stefan Nimmrichter
P1-132 - Scalable three-way quantum information tapping using parametric amplifiers
with quantum correlation
Nannan Liu, Xiaoying Li, Jiamin Li and Z. Y. Ou
P1-133 - Experimental demonstration of frequency-domain Hong-Ou-Mandel
interference
Toshiki Kobayashi, Rikizo Ikuta, Shuto Yasui, Shigehito Miki, Taro Yamashita, Hirotaka
Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto
P1-134 - Experimental Detection of Entanglement Polytopes via Local Filters
Yuanyuan Zhao, Markus Grassl, Bei Zeng and Guoyong Xiang
P1-135 - Computing Permanents for Boson Sampling on Tianhe-2 Supercomputer
Junjie Wu, Yong Liu, Baida Zhang, Xianmin Jin, Yang Wang, Huiquan Wang and Xuejun
Yang
P1-136 - Universal optimal device-independent witnessing of quantum channels
Michele Dall'Arno, Sarah Brandsen and Francesco Buscemi
P1-138 - Optimal communication via mixed quantum t designs
Sarah Brandsen, Michele Dall'Arno and Anna Szymusiak
P1-139 - Surpassing the no-cloning limit with a heralded hybrid linear amplifier
Jing Yan Haw, Jie Zhao, Josephine Dias, Syed Assad, Mark Bradshaw, Rémi Blandino,
Thomas Symul, Tim Ralph and Ping Koy Lam
P1-144 - Generation and storage of multimode entangled light in a solid state, spinwave quantum memory
Kate Ferguson, Sarah Beavan, Jevon Longdell and Matthew Sellars
P1-145 - Fast-gated single-photon counting with ultra-low noise based on
thermoelectrically cooled photomultiplier tube
Yanhui Cai, Zhengyong Li and Xiangkong Zhan
12
Poster Session II – Tuesday (5 July)
P2-146 - Kochen-Specker Theorem Proofs with Non-specific Projectors from Extended
KS Value Assignment Rules
Tang Weidong
P2-147 - Arbitrary Multi-Qubit Generation
Farid Shahandeh, Austin P. Lund, Timothy C. Ralph and Michael R. Vanner
P2-148 - Generation of photon pairs in a nonlinear waveguide array with
inhomogeneous poling pattern
Francesco Lenzini, James Titchener, Sachin Kasture, Alexander N. Poddubny, Andreas
Boes, Ben Haylock, Paul Fisher, Matteo Villa, Arnan Mitchell, Alexander S. Solntsev, Andrey
A. Sukhorukov and Mirko Lobino
P2-149 - Geometry of system-bath coupling and gauge fields: manipulating currents
and driving phase transitions
Chu Guo and Dario Poletti
P2-150 - Hong-Ou-Mandel interference between two collective excitations
Jun Li, Ming-Ti Zhou, Xiao-Hui Bao and Jian-Wei Pan
P2-151 - Nonlinear infrared spectrometer free from spectral selection
Anna Paterova, Shaun Lung, Dmitry Kalashnikov and Leonid Krivitsky
P2-152 - Secret key agreement demonstration over 7.8 km free-space optical channel
Mikio Fujiwara, Toshiyuki Ito, Mitsuo Kitamura, Hiroyuki Endo, Morio Toyoshima, Hideki
Takenaka, Yoshihisa Takayama, Ryosuke Shimizu, Masahiro Takeoka, Ryutaroh
Matsumoto and Masahide Sasaki
P2-153 - Interferometric Resolution of Incoherent Optical Point Sources near the
Quantum Limit
Ranjith Nair and Mankei Tsang
P2-155 - Efficient Large Block Codes Ancilla States Preparation for Fault-tolerant
Quantum Computation
Yi-Cong Zheng, Ching-Yi Lai and Todd Brun
P2-156 - Multi-photon experiments with solid-state single-photon sources
Marcelo Pereira de Almeida, Juan Carlos Loredo, Tau Bernstorff Lehmann, Nor Azwa
Zakaria, Paul Hiliare, Isabelle Sagnes, Aristide Lemaitre, Pascale Senellart and Andrew
White
P2-157 - Violation of steering inequality with path entangled single photon
Anthony Martin, Thiago Guerreiro, Fernando Monteiro, Jonatan Bohr Brask, Tamás Vertési,
Boris Korzh, Felix Bussieres, Varum Verma, Adriana Lita, Richard Mirin, Saewoo Nam,
Francesco Marsili, Matthew. Shaw, Nicolas Gisin, Nicolas Brunner, Hugo Zbinden and Rob
Thew
P2-158 - Experimental Demonstration of Continuous Variable One Sided Device
Independence
13
Nathan Walk, Sara Hosseini, Jiao Geng, Oliver Thearle, Jing Yan Haw, Seiji Armstrong,
Syed M. Assad, Jiri Janousek, Timothy C. Ralph, Thomas Symul, Howard Wiseman and
Ping Koy Lam
P2-160 - Detector-device-independent quantum key distribution
Anthony Martin, Alberto Boaron, Boris Korzh, Charles Lim, Gianluca Boso, Raphael
Houlmann and Hugo Zbinden
P2-161 - Heralded hybrid noiseless linear amplifier for arbitrary coherent states
Jie Zhao, Josephine Dias, Jing Yan Haw, Mark Bradshaw, Remi Blandino, Thomas Symul,
Timothy Ralph, Ping Koy Lam and Syed Assad
P2-162 - Quantum teleportation by quantum walks
Yun Shang
P2-163 - Characterizing ground and thermal states of few-body Hamiltonians
Otfried Guehne and Felix Huber
P2-164 - Classical realization of “quantum-optical coherence tomography” by timeresolved pulse interferometry
Kazuhisa Ogawa and Masao Kitano
P2-165 - Distribution of quantum coherence in multipartite systems
Chandrashekar Radhakrishnan, Manikandan Parthasarathy, Segar Jambulingam and Tim
Byrnes
P2-166 - Effects of measurement dependence on generalized CHSH-Bell test in the
single-run and multiple-run scenarios
Dan-Dan Li, Yu-Qian Zhou, Fei Gao, Xin-Hui Li and Qiao-Yan Wen
P2-167 - High fidelity entanglement swapping via a time-resolved coincidence
measurement
Yoshiaki Tsujimoto, Motoki Tanaka, Yukihiro Sugiura, Rikizo Ikuta, Shigehito Miki, Taro
Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto
P2-168 - Quantum metrology using topological quantum states.
Tim Byrnes
P2-169 - Ultrafast coherent control of Bose-Einstein condensates using stimulated
Raman adiabatic passage
Andreas Thomasen and Tim Byrnes
P2-170 - Generation and non-destructive detection of single microwave photons
Sankar Raman Sathyamoorthy
P2-171 - A correlation based entanglement criterion in bipartite multi-boson systems
Wiesław Laskowski, Marcin Markiewicz, Danny Rosseau, Tim Byrnes, Kamil Kostrzewa and
Adrian Kołodziejski
P2-172 - On the equivalence of separability and extendability of quantum states
K. R. Parthasarathy, Ritabrata Sengupta and B. V. Rajarama Bhat
14
P2-173 - Evaluation of quantum 1D repetition codes’ performance against quantum
noise
Takanori Sugiyama, Keisuke Fujii, Haruhisa Nagata and Fuyuhiko Tanaka
P2-174 - Monolithically integrated optics for scalable trapped-ion single-photon
sources
Mirko Lobino, Mojtaba Ghadimi, Valdis Blums, Benjamin G. Norton, Paul Fisher, Harley
Hayden, Jason Amini, Curtis Volin, Dave Kielpinski and Erik W Streed.
P2-175 - Detection-dependent six-photon NOON state interference
Rui-Bo Jin, Mikio Fujiwara, Ryosuke Shimizu, Robert Collins, Gerald Buller, Taro Yamashita,
Shigehito Miki, Hirotaka Terai, Masahiro Takeoka and Masahide Sasaki
P2-176 - Stationary Light in Resonant and Far-Detuned Atom-Optic Memories
Jesse Everett, Geoff Campbell, Young-Wook Cho, Pierre Vernaz-Gris, Daniel Higginbottom,
Olivier Pinel, Nick Robins, Ping Koy Lam and Ben Buchler
P2-177 - Particle-Indistinguishability Signatures in Phase Space
Farid Shahandeh
P2-179 - Temporal multimode storage of entangled photons
Peter C. Strassmann, Alexey Tiranov, Jonathan Lavoie, Nicolas Brunner, Marcus Huber,
Varun B. Verma, Sae Woo Nam, Richard P. Mirin, Adriana E. Lita, Francesco Marsili, Mikael
Afzelius, Félix Bussières, Nicolas Gisin
P2-180 - Au Microdisk-Size Dependence of Quantum Dot Emission from the Hybrid
Metal-Distributed Bragg Reflector Structures Employed for Single Photon Sources
Baoquan Sun
P2-182 - Quantum Carburettor Effect for Photon Number Shifting
Jennifer Radtke, John Jeffers and Daniel Oi
P2-183 - Noise-tolerant post-selected measurement using noise margin with GKP
code state
Kosuke Fukui, Akihisa Tomita and Atsushi Okamoto
P2-184 - An Optimal Design for Universal Multiport Interferometers
William Clements, Peter Humphreys, Benjamin Metcalf, Steven Kolthammer and Ian
Walmsley
P2-186 - Wavelength Conversion of non-classical light from rubidium atoms to the
telecom band
Rikizo Ikuta, Toshiki Kobayashi, Kenichiro Matsuki, Shigehito Miki, Taro Yamashita, Hirotaka
Terai, Takashi Yamamoto, Masato Koashi, Tetsuya Mukai and Nobuyuki Imoto
P2-187 - Few-Photon Heterodyne Spectroscopy
Gustavo Amaral, Thiago Ferreira Da Silva, Guilherme Temporão and Jean Pierre von der
Weid
P2-188 - Controlling two-photon frequency entanglement using cross-Kerr effect
Nobuyuki Matsuda
15
P2-189 - Experimental detection of entanglement with optimal-witness families
Jibo Dai, Yink Loong Len, Yong Siah Teo, Berthold-Georg Englert and Leonid A. Krivitsky
P2-190 - Irreversibility and the Arrow of Time in a Quenched Quantum System
Tiago Batalhao, Alexandre Souza, Roberto Sarthour, Ivan Oliveira, Mauro Paternostro, Eric
Lutz and Roberto Serra.
P2-191 - Simple and Efficient Memory-Assisted Quantum Key Distribution
Nicolo Lo Piparo, Mohsen Razavi and William Munro
P2-193 - An explicit classical strategy for winning a CHSH_q game
Matej Pivoluska and Martin Plesch
P2-194 - Isotropy and control of dissipative quantum dynamics
Ben Dive, Daniel Burgarth and Florian Mintert
P2-195 - Quantum Theory of Two-Dimensional Resolution for Two Incoherent Optical
Point Sources
Shan Zheng Ang, Ranjith Nair and Mankei Tsang
P2-197 - Unified view of quantum amplification based on quantum states
transformation
Mengjun Hu and Yongsheng Zhang
P2-198 - Two-atom interferences in a cavity QED system
Olivier Morin, Andreas Neuzner, Matthias Körber, Stephan Ritter and Gerhard Rempe
P2-199 - Exploring the limits of non-locality with pairs of photons
Alessandro Cere, Hou Shun Poh, Siddarth Koduru Joshi, Adán Cabello, Marcin Markiewicz,
Pawel Kurzynski, Dagomir Kaszlikowski and Christian Kurtsiefer.
P2-200 - Control and characterisation of nuclear spin memory in diamond
nanocrystals
Jan D. Beitner, Helena S. Knowles, Dhiren M. Kara, David-Dominik H. Jarausch and Mete
Atatüre
P2-201 - Long coherence time quantum memory for polarization qubits based on a
single atom in a cavity
Olivier Morin, Matthias Körber, Stefan Langenfeld, Andreas Neuzner, Stephan Ritter and
Gerhard Rempe
P2-202 - Quantum approaches to homomorphic encryption
Joshua Kettlewell, Carlos Perez-Delgado, Yingkai Ouyang, Si-Hui Tan, Li Yu, Lin Chen and
Joseph Fitzsimons
P2-204 - Silicon-vacancy: a colourful defect of diamond as solid-state single-spin for
quantum information.
Camille Stavrakas, Benjamin Pingault, Christian Hepp, Tina Müller, Mustafa Gündogan,
Jonas Becker, Carsten Schulte, Carsten Arend, Tillman Godde, Alexander Tartakovskii,
Matthew Markham, Christoph Becher, Elke Neu, Stefan Gsell, Matthias Schreck, Hadwig S
16
P2-205 - Photon Antibunching and Hong-Ou-Mandel Peak
Gustavo Amaral, Felipe Calliari, Thiago Ferreira Da Silva, Guilherme Temporão and Jean
Pierre von der Weid
P2-207 - Quantum assisted Gaussian process regression
Zhikuan Zhao, Jack Fitzsimons and Joseph Fitzsimons
P2-208 - Entanglement conditions for integrated-optics multi-port quantum
interferometry experiments
Junghee Ryu, Marcin Marciniak, Marcin Wiesniak and Marek Zukowski
P2-209 - Fault-tolerant Quantum Computation under non-Markovian noise
Jing Hao Chai and Hui Khoon Ng
P2-210 - Quantum Phase Transition and Universal Dynamics in the Rabi Model
Myung-Joong Hwang, Ricardo Puebla and Martin B. Plenio
P2-212 - Prospects for Atomic Spin-Squeezing inside Hollow-Core Photonic Crystal
Fiber
Zilong Chen and Shau-Yu Lan
P2-215 - Coherent manipulation of small ion Coulomb crystals in a Penning Trap
Pavel Hrmo, Manoj Joshi, Vincent Jarlaud, Joseph Goodwin, Graham Stutter and Richard
Thompson
P2-219 - Unifying wave-particle duality with entropic uncertainty
Patrick Coles, Jedrzej Kaniewski and Stephanie Wehner
P2-222 - Generalised phase kick-back: the structure of computational algorithms from
physical principles
Ciaran Lee and John Selby
P2-223 - Generation of single photons with highly tunable wave shape from a cold
atomic quantum memory
Pau Farrera, Georg Heinze, Boris Albrecht, Melvyn Ho, Matías Chávez, Colin Teo, Nicolas
Sangouard and Hugues de Riedmatten
P2-225 - High Efficiency Room-Temperature Raman Memory using Quenching
Sarah Thomas, Patrick Ledingham, Benjamin Brecht, Joseph Munns, Cheng Qiu, Amir
Feizpour, Ian Walmsley, Joshua Nunn and Dylan Saunders
P2-226 - Inertial Navigation using Atom Interferometry
Jimmy Stammers, Xiaxi Cheng and Ed Hinds
P2-231 - A Cavity-Enhanced Room-Temperature Broadband Quantum Memory for
Nanosecond Heralded Single Photons
Dylan Saunders, J. H. D. Munns, T. F. M. Champion, C. Qiu, S. E. Thomas, B. Brecht, K. T.
Kaczmarek, E. Poem, P. M. Ledingham, I. A. Walmsley and J. Nunn
P2-232 - Quantum parameter estimation with general dynamics
Haidong Yuan and Chi-Hang Fung
17
P2-233 - Modelling Atom-Filled Optical Cavities for Enhanced Light-Matter Interaction
Joseph Munns, Sarah E. Thomas, Benjamin Brecht, Patrick M. Ledingham, Ian A. Walmsley,
Joshua Nunn and Dylan J. Saunders
P2-234 - The Quantum-Classical Boundary for Precision Interferometric
Measurements
Patrick M. Birchall, Jeremy L. O'Brien, Jonathan C. F. Matthews and Hugo Cable
P2-235 - Entanglement is an inevitable feature of a non-classical universe
Jonathan Richens, John Selby and Sabri Al-Safi
P2-237 - The Quantum Simulation of Quantum Chemistry
Andrew Tranter, Peter Coveney, Florian Mintert and Peter Love
P2-240 - Optimal Wavelength Assignment in Hybrid Quantum-Classical DWDM
Networks
Sima Bahrani, Mohsen Razavi and Jawad A. Salehi
P2-241 - General method for constructing local-hidden-state (and -variable) models for
multiqubit entangled states
Rafael Rabelo, Daniel Cavalcanti, Leonardo Guerini and Paul Skrzypczyk
P2-242 - Towards Long Range Spin-Spin Interactions via Mechanical Resonators
Arthur Safira, Jan Gieseler, Aaron Kabcenell, Shimon Kolkowitz, Alexander Zibrov, Jack
Harris and Mikhail Lukin
P2-245 - Cold atom memory as a platform for quantum information
Geoff Campbell, Young-Wook Cho, Jian Su, Jesse Everett, Nicholas Robins, Ping Koy Lam
and Ben Buchler
P2-246 - Differential phase-time shifting protocol for QKD (DPTS)
Mario A. Usuga, Davide Bacco, Jesper Bjerge Christensen, Karsten Rottwitt, Leif K.
Oxenløwe and Yunhong Ding
P2-249 - Where does measurement uncertainty come from?
Filip Rozpedek, Jedrzej Kaniewski, Patrick J. Coles and Stephanie Wehner
P2-250 - Fisher Information and Quantum Communication with random unitary noise
Wiesław Laskowski, Marcin Markiewicz and Anna de Rosier
P2-252 - Numerical simulation of topological codes using tensor networks
Andrew Darmawan and David Poulin
P2-253 - Distributing entangled states using silicon photonic chips
Jianwei Wang, Damien Bonneau, Matteo Villa, Joshua Silverstone, Raffaele Santagati,
Shigehito Miki, Taro Yamashita, Mikio Fujiwara, Masahide Sasaki, Hirotaka Terai, Michael
Tanner, Chandra Natarajan, Robert Hadfield, Jeremy O'Brien and Mark Thompson
P2-256 - Floodlight Quantum Key Distribution
Zheshen Zhang, Quntao Zhuang, Justin Dove, Franco Wong and Jeffrey Shapiro
18
P2-258 - Symmetric Extendability of Quantum States and the Extreme Limits of
Quantum Key Distribution
Sumeet Khatri and Norbert Lutkenhaus
P2-259 - Large-Scale Simulation of the Quantum Internet
Rodney Van Meter, Shigeya Suzuki, Shota Nagayama, Takahiko Satoh, Takaaki Matsuo,
Amin Taherkhani, Simon Devitt and Joe Touch
P2-261 - Network-ready unconditional polarization qubit quantum memory at room
temperature
Eden Figueroa, Mehdi Namazi, Connor Kupchak, Bertus Jordaan and Reihaneh
Shahrokhshahi
P2-262 - Compact, integrated quantum key distribution sender module for hand-held
key exchange
Gwen Melen, Tobias Vogl, Markus Rau, Giacomo Corrielli, Andrea Crespi, Roberto
Osellame and Harald Weinfurter
P2-263 - Sub-Megahertz Single Photon Source
Markus Rambach, Aleksandrina Nikolova, Till J. Weinhold and Andrew G. White
P2-265 - Device-independent demonstration that a qubit is more than a quantum coin
Esteban S. Gómez, Santiago Gómez, Pablo González, Gustavo Cañas, Johanna F. Barra,
Aldo Delgado, Guilherme B. Xavier, Adán Cabello, Matthias Kleinmann, Tamás Vértesi and
Gustavo Lima
P2-266 - Optimal Efficiency of Heat Engines with Finite-Size Heat Baths
Hiroyasu Tajima and Masahito Hayashi
P2-267 - Self-guaranteed measurement-based quantum computation
Masahito Hayashi and Michal Hajdusek
P2-268 - Routing on a Quantum Internet
Takahiko Satoh, Shigeya Suzuki, Shota Nagayama, Takaaki Matsuo and Rodney Van Meter
P2-269 - Architecture of software simulation of a Quantum Internet
Shigeya Suzuki, Rodney Van Meter, Shota Nagayama, Takahiko Satoh and Takaaki Matsuo
P2-270 - Quantum Process Tomography of an Optically-Controlled Kerr Non-linearity
Bertus Jordaan, Connor Kupchak, Sam Rind and Eden Figueroa
P2-271 - Entanglement assisted classical communication simulates “classical
communication” without causal order
Seiseki Akibue, Masaki Owari, Go Kato and Mio Murao
P2-273 - Quantum information applications of highly ordered stoichiometric rare earth
crystals
Rose Ahlefeldt, Michael Hush and Matthew Sellars
P2-274 - One-way quantum computing with arbitrarily large time-frequency
continuous-variable cluster states from a single optical parametric oscillator
19
Rafael Alexander, Pei Wang, Niranjan Sridhar, Moran Chen, Olivier Pfister and Nicolas
Menicucci
P2-276 - Randomized benchmarking with cluster states
Rafael Alexander, Peter Turner and Stephen Bartlett
P2-277 - Simple approximation of minimum error probability for pure-state signals
Tsuyoshi Usuda and Shungo Asano
P2-280 - Determining the Quantum Fisher Information from Linear Response Theory
Tomohiro Shitara and Masahito Ueda
P2-282 - Cooling of a one-dimensional Bose gas
Bernhard Rauer, Pjotrs Grisins and Jörg Schmiedmayer
P2-283 - Concepts of non-Markovianity: a quantum hierarchy
Li Li, Michael Hall and Howard Wiseman
P2-284 - Topological pumping of photons in nonlinear coupled resonator arrays
Jirawat Tangpatinanon, Victor Bastidas, Dimitris Angelakis
20
Abstracts - Talks
Two Studies in Interferometry: Practical Metrology and Imperfect Boson Sampling
Carl Caves, University of New Mexico
Abstract: I will discuss two things, both briefly: quantum limits on practical quantum
metrology in which photons are cheaply available from a laser and all entanglement is
created at a beamsplitter and classical simulations of boson sampling in the presence of
losses and imperfections.
Quantum trajectories and past quantum states
Klaus Molmer, University of Aarhus, Denmark
Abstract: The state of a quantum system is described by a wavefunction evolving in time
according to the Schroedinger equation. If measurements are carried out on the system, its
wave function changes (collapses) according to the random outcome of the measurement.
During a sequence of measurements on a single system, its quantum state thus follows a
stochastic trajectory governed by the normal quantum mechanical time evolution, interrupted
by collapses at each measurement. The trajectory quantum state successfully predicts the
probabilities and mean values for the measurement of any physical observable – conditioned
on the results of previous measurements.
In this talk, I discuss how measurements at any moment of time do not only affect the
current and the future state of the system but they also supplement our knowledge about the
system at earlier times during the experiment. I shall show how such hindsight knowledge
can be formally defined as a time evolving “past quantum state”, which at any time depends
on all earlier and later measurement outcomes. I will show applications of this theory to
experiments on atoms and superconducting qubits, and I will discuss how the concept and
formalism of past quantum states relate to questions of more foundational character.
Entangling independent quantum-dot spins
Mete Atature, University of Cambridge
Abstract: Indistinguishable single photon generation is one of the key ingredients of a
photonic-based distributed quantum networks. Semiconductor quantum dots and colour
centres in diamond are example solid-state systems able to generate good quality single
photons and in parallel have a spin-defined ground state manifold. This opens the route to
spin-photon entangled nodes and the current challenges include both efficiency and quality
of spin-tagged photon generation. I will cover recent progress for efficient coupling and
entangling of quantum-dot spins, as well as a brief overview of future directions.
21
Time-resolved Scattering of a Single Photon by a Single Atom
Alessandro Cere, Centre for Quantum Technologies, NUS
Abstract: The efficiency of light-matter interfaces between single photons and single atoms
depends on the bandwidth and temporal shape of the single photon, and is crucial for
realistic implementations of many quantum information protocols. In particular, an
exponentially rising single photon is predicted to excite a single atom with a higher efficiency
compared to any other temporal shape [1]. A four-wave mixing photon pair source, in
conjunction with an asymmetric cavity, generates heralded single photons of tunable
bandwidth with exponentially decaying or rising shapes [2,3]. We combine the photon pair
source with a trapped single atom and investigate the free space scattering for different
bandwidths and temporal shapes.
We study the scattering dynamics by measuring the atomic emission and the reduction in
the number of transmitted photons. We observe that the atomic absorption dynamics are
imprinted in the single-photon excitation mode.
Infrared Spectroscopy with Visible Light
Leonid Krivitsky, Data Storage Institute
Abstract: We exploit the first-order interference of two Parametric Down Conversion (PDC)
sources to determine real and imaginary parts of the refractive index of media in the infrared
(IR) range. Frequency correlations of PDC enable determination properties of the medium at
IR wavelengths using conventional visible range optics and photodetectors.
Reference to: D. A. Kalashnikov, A. V. Paterova, S. P. Kulik and L. A. Krivitsky, «Infrared
spectroscopy with visible light», Nature Photonics, 10, 98–101 (2016).
Spectrally resolved white-light quantum interferometry for high-accuracy chromatic
dispersion measurements
Florian Kaiser, Université Nice Sophia Antipolis
Abstract: In quantum optical metrology, exploiting an N-photon N00N-state allows
performing phase sensing with better resolution compared to any classical approach
exploiting N photons.
Here, we introduce spectrally resolved white-light quantum interferometry which offers
advantages far beyond improving phase sensitivity. As opposed to the classical scheme, our
approach does not require balancing the interferometer which finds repercussions in speed,
robustness, and repeatability of the related experimental procedures. Additionally, by
simultaneously exploiting a N00N-state and energy-time entanglement, a simplified data
fitting function can be used which improves the accuracy significantly. As an exemplary
application, we exploit our scheme for measuring one of the most important parameters of
today's optical telecommunication networks and mode-locked laser design, namely
chromatic dispersion.
We repeat both quantum and classical dispersion measurements a 100 times on a 1 m long
standard single-mode fibre. Statistical data treatment shows that the quantum strategy is
more than three times more accurate compared state-of-the-art results, despite detecting
2.5*10^8 times less photons, which underlines that the improved accuracy is mainly due to
conceptual advantages enabled by quantum optics.
22
Applications of HyperEntanglement
Paul Kwiat, University of Illinois at Urbana-Champaign
Abstract: Entanglement is a critical resource for many quantum communication protocols.
Going further, photons that are simultaneously entangled in multiple degrees of freedom —
“hyperentangled” — enable enhanced protocols that would be difficult or impossible
otherwise. We will discuss our progress using hyperentangled photons from parametric
downconversion in several advanced quantum communication experiments, including
superdense teleportation and hyper dense coding.
Direct experimental reconstruction of the Bloch sphere
Matthew Pusey, Perimeter Institute for Theoretical Physics
Abstract: A focus of theoretical activity in quantum foundations has been looking at quantum
theory in a wide landscape of possible theories, called generalised probabilistic theories. In
particular, quantum theory has been "reconstructed" by finding axioms that single the theory
out from that landscape. We have taken a different approach to reconstruction, making as
few theoretical assumptions as possible but inputting the raw data from a qubit experiment. I
will show the resulting state space (spoiler: it's approximately a sphere) and discuss what we
can conclude using it. Joint work with Mike Mazurek, Kevin Resch, and Rob Spekkens.
Operational multipartite entanglement measures
Katharina Schwaiger, University of Innsbruck
Abstract: Entanglement is the resource to overcome the natural limitations of spatially
separated parties restricted to local operations assisted by classical communication (LOCC)
and hence, an entanglement measure is a function that is nonincreasing under LOCC. We
recently introduced two operational entanglement measures, the source and the accessible
entanglement, that are applicable for arbitrary multipartite (pure or mixed) states. Whereas
the accessible entanglement characterizes the potentiality of a state to generate other states
via LOCC, the source entanglement characterizes the simplicity of generating the state at
hand. Furthermore, these measures can be generalized to two classes of entanglement
measures.
In this talk I will first introduce the two new operational entanglement measures. Then we will
consider pure bipartite as well as multipartite states, show how we can derive explicit
formulas for the source and accessible entanglement and use the new entanglement
measures to characterize the entanglement contained in e.g. three-qubit states.
Entanglement of temporal order from quantum theory and gravity
Magdalena Zych, University of Queensland
Abstract: Violations of Bell's theorem show that physical quantities cannot have preassigned values. However, the causal relations between events — e.g. operations or
measurements on a system — are assumed to be fixed by the "underlying" space-time
structure. Yet, according to general relativity space-time is a dynamical object and causal
relations can be changed by the distribution of massive objects. Here, I will present a direct
example of a non-classical causal structure arising from quantum theory and gravity: when a
massive object is prepared in a specific quantum state the order between a pair of time-like
events can become "entangled" with the order between another pair of time-like events. In
the spirit of Bell’s theorem, I will formulate a task which can be achieved by agents exploiting
“entanglement” of temporal order, and which is impossible if temporal order was predefined.
23
A Many-Interacting-Worlds Approach To Quantum Mechanics
Michael Hall, Griffith University
Abstract: When one applies quantum mechanics to our world, we require a wave function
that has support over an enormous configuration space, where each point specifies the
positions of all particles and the values of all fields. In the usual many worlds picture, this
wave function decomposes into many branches, all 'real' but having different statistical
weights and no interactions between them. In the deBroglie-Bohm picture, just one point in
the configuration space is 'real', with its evolution determined by the wave function but not
vice versa.
In contrast, in our recently proposed many-interacting-worlds approach [1] there is no wave
function at all. Instead, there are a large but finite number of 'real' worlds, corresponding to
different points in the configuration space. These worlds would each evolve classically,
except for a universal interaction force acting between worlds. This force essentially acts to
'repel' nearby worlds in configuration space, and is responsible for all quantum effects.
Probabilities arise as equally-weighted averages over the worlds, corresponding to
ignorance as to which world a given observer occupies. Quantum predictions are recovered
in the limit of an infinite number of worlds. This approach provides a new way of thinking
about quantum phenomena, such as tunneling, zero-point energies and entanglement, as
well as an interesting example of how to 'tweak' quantum mechanics without (apparently)
breaking it. More practically, it also suggests a new method of approximating quantum
evolution for large systems.
[1] M.J.W. Hall, D.-A. Deckert and H.M. Wiseman, Physical Review X 4 (2014) 041013.
Experimental Nonlocal and Surreal Bohmian Trajectories
Howard Wiseman, Griffith University
Abstract: Weak measurement allows one to empirically determine a set of average
trajectories for an ensemble of quantum particles. However, when two particles are
entangled, the trajectories of the first particle can depend non-locally on the position of the
second particle. Moreover, the theory describing these trajectories, called Bohmian
mechanics, predicts trajectories which were at first deemed ``surreal'' when the second
particle is used to probe the position of the first particle. Here, we entangle two photons and
measure a set of Bohmian trajectories of one of them, using weak measurements and postselection. We show that the choice of intervention on one particle affects the trajectories of
the other, and that the trajectories seem ``surreal'' only if one ignores this manifest
nonlocality.
Quantum dot quantum computing
Andrew Doherty, University of Sydney
Abstract: Gate-defined semiconductor devices are a promising avenue for implementing
quantum computation. Many approaches to performing two-qubit gates have been proposed
in the literature and tested in the laboratory. I will discuss our recent theoretical studies of
exchange-based two-qubit gates in the context of current experimental work in GaAs. In this
approach leakage errors that would typically occur are suppressed by designing the system
such that they are energy non-conserving, and through the use of adiabatic control pulses.
The resulting two-qubit operations can be as fast as single-qubit gates.
24
Quantum Computing in Silicon with Donors
Michelle Simmons, University of New South Wales
Abstract: Extremely long electron and nuclear spin coherence times have recently been
demonstrated in isotopically pure Si-28 [1,2] making silicon one of the most promising
semiconductor materials for spin based quantum information. The two level spin state of
single electrons bound to shallow phosphorus donors in silicon in particular provide well
defined, reproducible qubits [3] and represent a promising system for a scalable quantum
computer in silicon. An important challenge in these systems is the realisation of an
architecture, where we can position donors within a crystalline environment with approx. 2050nm separation, individually address each donor, manipulate the electron spins using ESR
techniques and read-out their spin states.
We have developed a unique fabrication strategy for a scalable quantum computer in silicon
using scanning tunneling microscope hydrogen lithography to precisely position individual P
donors in a Si crystal [4] aligned with nanoscale precision to local control gates [5] necessary
to initialize, manipulate, and read-out the spin states [6]. During this talk I will focus on
demonstrating spin transport [7] and single-shot spin read-out of precisely-positioned P
donors in Si. I will also describe our approaches to scale up using rf reflectometry [8] and the
investigation of 3D architectures for implementation of the surface code [9].
[1] K. Saeedi et al., Science 342, 130 (2013).
[2] J. T. Muhonen et al., Nature Nanotechnology 9, 986 (2014).
[3] B.E. Kane, Nature 393, 133 (1998).
[4] M. Fuechsle et al., Nature Nanotechnology 7, 242 (2012).
[5] B. Weber et al., Science 335, 6064 (2012).
[6] H. Buch et al., Nature Communications 4, 2017 (2013).
[7] B. Weber et al., Nature Nanotechnology 9, 430 (2014).
[8] M.G. House et al., Nature Communications 6, 8848 (2015)
[9] C. Hill et al., Science Advances 1, e1500707 (2015).
Coherent feedback of a single qubit in diamond
Paola Cappellaro, Massachusetts Institute of Technology
Abstract: The most common approach to engineering desired operations on qubits subjected
to the deleterious effects of their environment relies on open-loop quantum control
techniques. Feedback control, an alternative strategy inspired by the success of classical
control, is less pervasive in the quantum setting because of the complications introduced by
quantum measurement. I will present the experimental implementation of a feedback-control
algorithm with a solid-state spin qubit associated with the nitrogen vacancy centre in
diamond. The algorithm exploits coherent feedback to overcome the limitations of
measurement-based feedback. The feedback algorithm can protect the qubit against intrinsic
dephasing noise for milliseconds (orders of magnitude larger than the qubit dephasing time)
by exploiting a long-lived ancillary qubit. In addition, it can protect the qubit coherence, while
performing two essential qubit gates—NOOP and NOT gates—during the protection time.
25
Concurrent Remote Entanglement of Transmon Qubits using Flying Photons
Anirudh Narla, Department of Applied Physics, Yale University
Abstract: Concurrent remote entanglement is an essential primitive in quantum information
science. It consists of entangling on demand two arbitrary, distant quantum systems which
never directly interact. In quantum optics, concurrent remote entanglement experiments
have recently provided loophole-free tests of quantum non-locality and form the basis for the
modular architecture of quantum computing. In these experiments, the Alice and Bob qubits
are each first entangled with their respective traveling photons. Subsequently, the two
photon paths interfere on a beam-splitter, which acts as a which-path eraser, and are then
directed to single-photon detectors. A key feature of this concurrent remote entanglement
protocol is its robustness to photon losses, unlike schemes that rely on continuous variable
states. This robustness arises from heralding the entanglement on the detection of events
which can be selected for their unambiguity and are uniquely linked to the production of a
pure entangled state. Here we demonstrate this protocol in the domain of superconducting
quantum circuits where the natural carriers of information between modules are traveling
microwave photons. Our demonstration exploits, in a single experiment, a set of tools that
had been previously the exclusive privilege of quantum optics experiments, namely
microwave single-photon sources and detectors together with the spatial and temporal
control of these photons to make them indistinguishable. With these tools, we have realized
the which-path erasure of microwave photons and thus the generation of loss-tolerant
entanglement between distant superconducting qubits by concurrent measurements. The
protocol speed and prospects for improving fidelity make this a very promising
implementation for the distribution of quantum information with microwave flying photons.
Our experiment opens for superconducting qubits the new prospect of modular quantum
information.
High fidelity transfer and storage of photon states in a single nuclear spin
Sen Yang, 3. Physikalisches Institut, Uni Stuttgart
Abstract: Photons are natural carriers of quantum information over long distances. Matter
systems have good storage capabilities and processing qubits. However, it is challenging to
integrate all these capabilities into one system.
The nitrogen-vacancy (NV) defect center in diamond does show significant potential for
realizing solid-state quantum networks. The NV center provides a hybrid spin system in
which electron spins are used for fast, high-fidelity control and readout, and nuclear spins
are well-isolated from their environment yielding ultra-long coherence time. Electron and
nuclear spins could form a small-scale quantum register. A so far missing link is to store
quantum information from a light field into the defects spins in such a way that scalable
quantum repeater networks is possible. Here we demonstrate a new scheme based on the
interaction of an optical photon and a hybrid electron-nuclear spin system. The storage
process is achieved by coherently transferring a single photon to an entangled electronnuclear spin state of a nitrogen vacancy center in diamond. The process resembles a
photon-nuclear spin. We demonstrate this scheme by storage of a photon qubit in a single
solid-state nuclear spin qubit with average fidelity ~98% and storage time of 10 seconds. By
choosing a particular optically excited state, the nuclear spin storage is made robust against
over 1000 rounds repetitive excitation of the electron spin, a key requirement for a versatile
quantum node. The photon-nuclear spin interface and the nuclear spin storage
demonstrated here constitutes a further step towards a practical solid-state quantum network
comprising diamond spins and photons.
Reference: Yang, et al, arXiv:1511.04939 (2015)
26
Quantum State Engineering using Hybridization
William Munro, NTT Basic Research Laboratories
Abstract: The development of quantum information enabled technologies has reached an
interesting stage where we can now in principle engineer composite systems to exploit the
best properties of these individual systems. Hybridisation allows us to undertake operations
and tasks that may otherwise prove difficult. In this presentation we show how by strongly
coupling an ensemble of electron spins hosted by nitrogen-vacancy centers in diamond to a
superconducting circuit, the coherence properties of the composite system can be
significantly increased, even beyond those of the ensemble or the superconducting circuit.
Our research opens up a path towards long lived quantum memories, solid-state microwave
frequency combs and points to a new route to cavity QED experiments with dense spin
ensembles where the direct dipole-dipole interaction between spins becomes important and
many-body phenomena will be directly accessible.
Atomic to generalized Hong-Ou-Mandel interference: probing entanglement in the
dynamics of many-body systems
Adam Kaufman, Harvard University
Abstract: Entanglement within a many-body system is a defining feature of strongly
correlated quantum systems. Recent theoretical developments point to the entropy of
entanglement as a means to classify unusual quantum phases, such as spin liquids and
topological phases. In this talk I will present an experimental scheme to probe entanglement
in itinerant systems of bosons. By employing techniques used to observe atomic Hong-OuMandel interference, it is possible to perform many-body interference that probes the
indistinguishability of quantum states. I will discuss how this interference allows us to
measure quantum purity, second order Rényi (entanglement) entropy and mutual
information within finite Bose-Hubbard chains. In the context of these techniques, I will focus
on our investigation of the dynamics of quenched, isolated Bose-Hubbard chains. Here we
observe that thermal ensembles appear to emerge from a pure quantum state, while the
entanglement entropy quantitatively approaches the thermal entropy. Our observations
experimentally illustrate the role of entanglement in facilitating thermalization of pure
systems undergoing unitary dynamics.
Comparing Experiments to the Fault-Tolerance Threshold
Steve Flammia, The University of Sydney
Abstract: Achieving error rates that meet or exceed the fault-tolerance threshold is a central
goal for quantum computing experiments, and measuring these error rates using
randomized benchmarking is now routine. However, direct comparison between measured
error rates and thresholds is complicated by the fact that benchmarking estimates average
error rates while thresholds reflect worst-case behavior. These two can differ by orders of
magnitude in the regime of interest. I will discuss how to facilitate comparison between the
experimentally accessible average error rates and the worst-case quantities that arise in
current threshold theorems by describing relations between the two for a variety of physical
noise sources, including dephasing, thermal relaxation, coherent and incoherent leakage, as
well as coherent unitary over and under rotation. The results indicate that it is coherent
errors that lead to an enormous mismatch between average and worst case, and we quantify
how well these errors must be controlled to ensure fair comparison between average error
probabilities and fault-tolerance thresholds. Finally, I will describe how a recently introduced
measure of coherent errors called the unitarity can sometimes be used to directly quantify
the distance to the threshold based on data collected from randomized benchmarking
experiments.
27
Recent experimental progress in quantum communication
Qiang Zhang, University of Science and Technology of China, Shanghai
Abstract: Quantum-communication network is believed to be the next-generation platform for
remote information processing tasks, including unconditional secure communication,
communication complexity reduction and etc. In this talk, I shall review the recent experiment
progress in measurement device independent quantum key distribution. Also, we shall talk
about a recent experiment, which implements quantum finger printing beating the classical
limit.
Secure Multi-party Computing
(From Classical to Quantum - From Linearity to Nonlinearity)
Elham Kashefi, University of Edinburgh
Abstract: to be updated
Unstructured quantum key distribution
Patrick Coles, University of Waterloo
Abstract: Quantum key distribution (QKD) allows for communication with security guaranteed
by quantum theory. The main theoretical problem in QKD is to calculate the secret key rate
for a given protocol. Analytical formulas are known for protocols with symmetries, since
symmetry simplifies the analysis. However, experimental imperfections break symmetries,
hence the effect of imperfections on key rates is difficult to estimate. Furthermore, it is an
interesting question whether (intentionally) asymmetric protocols could outperform
symmetric ones. In this work, we develop a robust numerical approach for calculating the
key rate for arbitrary discrete-variable QKD protocols. Ultimately this will allow researchers to
study ``unstructured'' protocols, i.e., those that lack symmetry. Our approach relies on
transforming the key rate calculation to the dual optimization problem, which dramatically
reduces the number of parameters and hence the calculation time. We illustrate our method
by investigating some unstructured protocols for which the key rate was previously unknown.
28
Experimental Quantum Communications
polarization degrees of freedom
Paolo Villoresi, Università degli Studi di Padova
in
Space
exploiting
temporal
and
Abstract: Quantum Communications (QC) in Space are gaining a strong momentum for both
providing the way to realize tests on the interplay of Quantum Physics and Gravity on very
long scale and for terminals in relative motion as well as to provide a network of secure
communications on planetary scale.
In the perspective to extend the realm of QC toward larger distances, we would like to
present the extension of the single photons exchange, initially demonstrated for LEO orbits
to a source in MEO orbit.
Moreover, we would like to report on the experiment using the temporal modes of light as the
physical degree of freedom used for the encoding of the qubit [6]. This represent an
evolution with respect to the polarization of the photon, used in the first demonstration of QC
in Space.
These QC experiments were realized at MLRO - Matera Laser Ranging Observatory of the
ASI Italian Space Agency, in Matera, Italy.
Quantum teleportation over deployed fibres and applications to quantum networks
Daniel Oblak, University of Calgary
Abstract: Quantum teleportation allows the disembodied transfer of a quantum state
between two distant objects. For instance a photon interacting with one member of an
entangled photon pair, by means of a so-called Bell-state measurement, will have its state
transferred onto the second member of the pair. Starting in 1998, this puzzling prediction of
quantum mechanics has been demonstrated by many groups around the world; however,
with one very recent exception by Hensen et al., only the photon that received the teleported
state, if any, traveled over a long distance while the photons partaking in the Bell-state
measurement were always measured closely to where they had been created.
Here, taking advantage of the Calgary metropolitan fibre network, we report the teleportation
of a quantum state from a telecommunication-wavelength photon, interacting with another
telecommunication photon after both have travelled in bee-line over several kilometres, onto
a photon at 795 nm wavelength. This improves the state-of-the-art in terms of teleportation
distance - which we define in the arguably most natural way to be the spatial separation
between the locations of the Bell-state measurement and that of the photon, at the time of
this measurement, that receives the teleported state - by almost one order of magnitude
from 818 m to 6.2 km, thereby establishing an important requirement for quantum repeaterbased communications. Our demonstration, which is compatible with quantum memory for
light (another key component of a quantum repeater), verifies quantum teleportation over a
truly macroscopic distance, and constitutes an important milestone towards the creation of a
global quantum internet.
29
Fault-tolerant Holonomic Quantum Computation in Surface Codes
Yi-Cong Zheng, Centre of Quantum Techonlogy
Abstract: We show that universal holonomic quantum computation (HQC) can be achieved
fault-tolerantly by adiabatically deforming the gapped stabilizer Hamiltonian of the surface
code, where quantum information is encoded in the degenerate ground space of the system
Hamiltonian. We explicitly propose procedures to perform each logical operation, including
logical state initialization, logical state measurement, logical CNOT, state injection and
distillation,etc. In particular, adiabatic braiding of different types of holes on the surface leads
to a topologically protected, non-Abelian geometric logical CNOT. Throughout the computation,
quantum information is protected from both small perturbations and low weight thermal
excitations by a constant energy gap, and is independent of the system size. Also the
Hamiltonian terms have weight at most four during the whole process. The effect of thermal
error propagation is considered during the adiabatic code deformation. With the help of
active error correction, this scheme is fault-tolerant, in the sense that the computation time
can be arbitrarily long for large enough lattice size. It is shown that the frequency of error
correction and the physical resources needed can be greatly reduced by the constant energy
gap.
From the first loophole-free Bell test to a quantum Internet
Ronald Hanson, QuTech and Kavli Institute of Nanoscience, Delft University of Technology
Abstract: The realization of a highly connected network of qubit registers is a central
challenge for quantum information processing and long-distance quantum communication.
Diamond spins associated with NV centers are promising building blocks for such a network
as they combine a coherent optical interface [1] (similar to that of trapped atomic qubits) with
a local register of robust and well-controlled nuclear spin qubits [2]. Here we present our
latest progress towards scalable quantum networks, including the first loophole-free violation
of Bell’s inequalities [3,4] and the realization of a robust quantum network memory with
nuclear spin qubits using decoherence-protected subspaces [5].
[1] W. Pfaff et al., Science 345, 532 (2014).
[2] J. Cramer et al., Nature Comm. 7, 11526 (2016).
[3] B. Hensen et al., Nature 526, 682 (2015).
[4] B. Hensen et al., arXiv:1603.05705 (2016).
[5] A. Reiserer et al., Phys. Rev. X 6, 021040 (2016).
Significant-loophole-free test of local realism with entangled photons
Marissa Giustina, University of Vienna
Abstract: Local realism is the worldview in which physical properties of objects exist
independently of measurement and where physical influences cannot travel faster than the
speed of light. Bell’s theorem states that this worldview is incompatible with the predictions
of quantum mechanics, as is expressed in Bell’s inequalities. Previous experiments
convincingly supported the quantum predictions. Yet, every experiment requires
assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test
that closes the most significant of these loopholes simultaneously. Using a well-optimized
source of entangled photons, rapid setting generation, and highly efficient superconducting
detectors, we observe a violation of a Bell inequality with high statistical significance.
30
A strong loophole-free test of Local Realism
Krister Shalm, NIST
Abstract: We present a loophole-free violation of local realism using entangled photon pairs.
All relevant events in our Bell test are spacelike separated, and we use a high-quality
polarization-entangled source of photons, combined with high-efficiency single-photon
detectors to observe a statistically strong violation of a Bell inequality.
Event-ready loophole free Bell test using heralded atom-atom entanglement
Harald Weinfurter, University of Munich
Abstract: Atom-photon entanglement together with entanglement swapping forms the basis
for an event-ready Bell experiment closing the detection as well as the locality loophole.
Entanglement between atoms separated by 400 m and fast state-dependent ionisation of the
atoms enables space-like separated observers. We observe an S-value of S=2.54+/-0.24
disvalidating local realistic theories with high confidence.
Bell correlations in a Bose-Einstein condensate
Roman Schmied, University of Basel
Abstract: The results of measurements by different observers can show correlations that are
stronger than any classical theory allows. These Bell correlations (or nonlocal correlations)
can be confirmed by violating a Bell inequality, for which quantum entanglement is
necessary but insufficient. Tremendous progress has been made recently in characterizing
many-body systems through the entanglement of their constituent bodies. However, even
though multi-partite Bell inequalities are known, the detection of Bell correlations in large
systems has remained elusive, due to the lack of suitable measurement schemes that can
be implemented with limited detection resolution and acquisition time.
We have experimentally demonstrated Bell correlations between the particles of a spinsqueezed Bose-Einstein condensate of about 480 rubidium-87 atoms [1]. This means that
Bell correlations are present in moderately entangled and experimentally accessible manybody systems, and that they can be revealed by collective and coarse-grained
measurements. Consequently, a locally causal description of the world does not necessarily
become more adequate as the system size increases.
We derive our Bell correlation witness from a recent Bell inequality involving only one- and
two-body correlation functions [2], which gives it a natural scalability to large systems. While
it does not provide a loophole-free and device-independent Bell test, it is a powerful tool for
characterizing correlations in many-body systems state-independently. Our witness and its
application to spin-squeezed states open the way for using many-body systems as probes
into the epistemic nature of our world, as well as for quantum information tasks such as
certified randomness generation with high rates.
[1] R. Schmied, J.-D. Bancal, B. Allard, M. Fadel, V. Scarani, P. Treutlein, N. Sangouard:
Science 352, 441 (2016).
[2] J. Tura, R. Augusiak, A. B. Sainz, T. Vértesi, M. Lewenstein, A. Acín: Science 344, 1256
(2014).
31
A Schrodinger Cat Living in Two Boxes
Yvonne Gao, Yale University
Abstract: Quantum superpositions of distinct coherent states in a single-mode harmonic
oscillator, known as “cat states”, have been an elegant demonstration of Schr¨odinger’s
famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in two
microwave cavities bridged by a superconducting artificial atom, which can also be viewed
as an entangled pair of single-cavity cat states. We present full quantum state tomography of
this complex cat state over a Hilbert space exceeding 100 dimensions via quantum nondemolition measurements of the joint photon number parity. The ability to manipulate such
multi-cavity quantum states paves the way for logical operations between redundantly
encoded qubits for fault-tolerant quantum computation and communication.
Large-amplitude squeezed optical Schrödinger cat states with minimized nonGaussian operational cost
Hanna Le Jeannic, Laboratoire Kastler Brossel
Abstract: The generation of freely-propagating large coherent-state superposition (CSS) is a
critical capability in the context of the optical hybrid quantum information approach.
However, their generation at a reasonable preparation rate remains challenging.
We recently proposed and implemented a novel optical scheme enabling their heralded
generation.
Based on two-mode squeezed vacuum, linear mixing, and a n-photon detection performed
on one of the modes, the process allowed to optimize the formation of the CSS in a versatile
way, focusing all the non-Gaussian resources to prepare only the non-Gaussian part of the
state.
Using such a strategy, we demonstrated the experimental realization of large-amplitude
squeezed CSS with a size |α|²=3 and a fidelity of 80%.
The developed protocol and the achieved preparation rate make these states suitable as
initial resources for subsequent quantum information protocols.
Qomputer Science at Microsoft Research
Alex Bocharov, Microsoft
Abstract: Over the course of three decades, quantum algorithms have been developed that
offer fast solutions to problems in a variety of fields including cryptography, number theory,
optimization, chemistry, physics, and materials science. The parallel advance of quantum
devices necessitates the development of software tools and platforms for programming,
harnessing, and controlling a quantum computer. I will give a brief overview of Microsoft’s
directions in quantum computation, focusing on recent work of the Quantum Architectures
and Computation (QuArC) group. I will discuss promising applications of quantum
computers, as well as Computer science methods and software techniques required to
implement such applications in simulation and in real hardware.
32
Industrializing qubits through automation
Julian Kelly, Google
Abstract: Recent advances in fidelity of digital superconducting qubits have enabled complex
demonstrations of error correction and quantum simulation, highlighting their potential as a
useful computational resource. However, scaling these experiments to numbers of qubits
that are classically intractable will require significant advances in quantum control. In
particular, operating systems of qubits with high fidelity requires some level of human
intervention, hindering scalability. Although components of qubit control are typically
automated, a full system solution is needed. Here, we present a framework for bootstrapping
and diagnosing qubits fully autonomously by relating control calibrations as a directed graph.
We demonstrate how this system can be used to scale control of many qubits, as well as
assist in industrializing qubit manufacturing and characterization.
Quantum @ NTT
William Munro, NTT
Abstract: The mission of NTT's Basic Research Laboratory is the promotion of advances in
science and its contribution to our future business. To achieve these missions, we conduct
basic research in the fields of Materials Science, Physical Science and Optical Science.
Quantum Science is one such area where we have significant expertise in photonics, solidstate, superconducting and hybrid systems. In this presentation, we will highlight our recent
developments in these area and discuss our future direction, indicating why fundamental
research is so important.
D-Wave's Approach to Quantum Computing: 1000-qubits and Counting!
Colin William, Dwave
Abstract: In this talk I will describe D-Wave's approach to quantum computing, including the
system architecture of our 1000-qubit D-Wave 2X, its programming model, and performance
benchmarks. Furthermore, I will describe how the native optimization and sampling
capabilities of the quantum processor can be exploited to tackle problems in a variety of
fields including medicine, machine learning, and computational finance.
33
Hybrid quantum systems using magnons in a ferromagnetic crystal
Yasunobu Nakamura, University of Tokyo
Abstract: Collective excitations in solids sometime have long coherence times useful for
quantum information processing. Superconducting qubits are the most advanced and
successful example among them. In addition to long-lived harmonic oscillator modes found
in superconducting resonators and cavities, nonlinearity brought by Josephson junctions
plays a crucial role in quantum state control and measurement in superconducting quantum
circuits.
Now it is natural to apply the excellent quantum tools to other quantum systems. We are
particularly interested in controlling other collective excitations in solids. It will expand the
territory of our quantum technologies and give rise to quantum interfaces and transducers
between various physical systems with different energy scales, which could be useful for
quantum communication and sensing.
In this talk, I will review our recent activities on quantum magnonics using a millimeter-scale
ferromagnetic sphere as an example of such hybrid quantum systems. The collective spin
excitations in the sphere, in particular the uniform spin precession, are strongly coupled with
a microwave cavity mode [1] and then indirectly with a superconducting qubit [2]. The
magnon-induced vacuum Rabi splitting observed in the system indicates that we can readily
apply the well-established schemes of cavity (circuit) QED to magnons and manipulate and
measure their quantum states. I will also discuss interaction between the collective spin
excitations and infrared light and present experimental results on optomagnonics [3,4].
[1] Y. Tabuchi et al., Phys. Rev. Lett. 113, 083603 (2014).
[2] Y. Tabuchi et al., Science 349, 405 (2015); arXiv:1508.05290.
[3] R. Hisatomi et al., Phys. Rev. B. 93, 174427 (2016).
[4] A. Osada et al., Phys. Rev. Lett. 116, 223601 (2016).
Quantum Correlation between photons and single spin-waves in a solid-state
environment
Hugues De Riedmatten, ICFO-The Institute of Photonic Sciences
Abstract: Quantum correlations between photons (ideally at telecom wavelengths) and longlived spin-waves in quantum memories is an important resource for the distribution of
quantum information to remote locations, using quantum repeater architectures. In this talk, I
will focus on single spin-waves in a solid-state environment. Rare-earth (RE) doped crystals
are promising candidates as quantum memories for light as they offer coherence properties
comparable to those of atomic systems, but free of the drawbacks deriving from atomic
motion. The research on RE based quantum memories has been so far mostly focused on
the mapping of photonic quantum bits to optical collective excitations, but this leads to short
lived and mostly pre-determined storage. However, some RE ions, as Praseodymium and
Europium, exhibit the suitable energy level scheme, with three long-lived hyperfine ground
states, to enable the spin-wave storage by transferring the collective optical excitations into
collective spin excitations [1,2]. I will present our recent and current efforts towards the
realization of quantum correlation between photons and long-lived single spin-waves in a
Praseodymium doped crystal, following two different approaches. One approach consists in
storing a single photon from a non-degenerate correlated pair generated by cavity enhanced
spontaneous down conversion [3] in a solid state spin-wave quantum memory, leading to
strong quantum correlation between a telecom photon and a solid-state spin wave. The
other approach consists in using the quantum memory as a source of correlated photon pair
34
with embedded memory. Finally, I will present a new approach towards the demonstration
of solid-state integrated quantum memories, using laser-written waveguides [4].
[1] M. Gündoğan, P. M. Ledingham, K. Kutluer, M. Mazzera and H. de Riedmatten , A solid
state spin-wave quantum memory for time-bin qubits, Phys. Rev. Lett. 114, 230501 (2015)
[2] P. Jobez, C. Laplane, N. Timoney, N. Gisin, A. Ferrier, P. Goldner, and M. Afzelius,
Coherent Spin Control at the Quantum Level in an Ensemble-Based Optical Memory, Phys.
Rev. Lett. 114, 230502 (2015)
[3] J. Fekete, D. Rieländer, M. Cristiani, and H. de Riedmatten, Ultranarrow-Band PhotonPair Source Compatible with Solid State Quantum Memories and Telecommunication
Networks
Phys. Rev. Lett. 110, 220502 (2013)
[4] G. Corrielli, A. Seri, M. Mazzera, R. Osellame and H. de Riedmatten, “An integrated
optical memory based on laser written waveguides”, Phys. Rev. Applied 5, 054013 (2016)
Towards a photon-phonon quantum interface
Sungkun Hong, University of Vienna
Abstract: Interfacing a single photon with various quantum degrees of freedom is an
outstanding problem in modern quantum information science. For instance, it allows for
manipulation and long-distance communication of remote quantum systems such as spin
states of atoms, atomic ensembles or solid-state qubits. Recently, micro-fabricated
mechanical devices have been considered as possible building blocks for quantum
information architectures. They combine an engineerable solid-state platform on the
nanoscale with the possibility to coherently interact with a variety of physical systems, which
allows for mechanics-based hybrid quantum systems that interconnect different qubits
through mechanical modes. I will discuss the implementation of a protocol (based on the
probabilistic DLCZ scheme) to realize quantum interface between single phonons of a nanomechanical device and single optical photons. In particular, I will present our recent
demonstration of non-classical correlations between single photons and phonons in a microfabricated optomechanical resonator, which is the first step towards photon-phonon quantum
interface.
Generation of Mechanical Interference
Measurement
Michael Vanner, University of Oxford
Fringes
by
Multi-Photon
Quantum
Abstract: One of the cornerstones of quantum mechanics is that matter can possess both
particle- and wave-like properties. Since the inception of quantum mechanics, such wavelike
behaviour has been observed in ever more massive systems - ranging from electrons,
neutrons, ultracold atoms, and even large molecules comprising many hundreds of atoms.
An exciting route to further extend the exploration of quantum phenomena to a macroscopic
regime is through the study of quantum optomechanics where optical fields are used to
manipulate the motion of mechanical resonators using radiation pressure. In contrast to a
two-slit experiment, a mechanical oscillator can exhibit interference fringes in a quadrature of
motion (analogous to the pattern on a distant screen) where the superposition is in the
conjugate quadrature (analogous to the wavefunction at the slits). Thus far, mechanical
interference fringes have only been observed in microscopic mechanical resonators - single
trapped ions. Here we report the observation of mechanical interference fringes in the
motion of a macroscopic membrane comprising 10^16 atoms [1].
Our experiment to generate and observe mechanical interference fringes consists of a SiN
membrane forming part of two optical interferometers. One of the interferometers uses single
photon detection to generate non-Gaussian mechanical states and the other uses an
independent optical field to reconstruct the mechanical phase-space distribution. By counting
35
a single photon in the output of the state preparation interferometer the optical field is
projected into a path entangled number state. When the mechanical resonator interacts with
this optical state it will then experience a superposition of a momentum transfer (single
photon present) and the identity operation (no photon present), and interference fringes will
be generated in the mechanical position distribution. The size of the superposition that can
be generated, and indeed the frequency of the mechanical interference fringes, can be
enhanced by projecting the optical field onto a N00N state, where the momentum transfer to
the mechanical oscillator is enhanced by a factor of N. We have experimentally observed a
factor of two increase in the mechanical interference fringe frequency by projection onto a
two-photon N00N state, where the phase super-resolution of the measurement is mapped to
the mechanical motion.
We would like to highlight that our approach can generate non-classical mechanical states,
which exhibit Wigner negativity, independent of the mechanical thermal occupation and the
optomechanical coupling strength.
Moreover, the scheme is resilient to loss, and can be readily applied to other optomechanical
and bosonic systems more broadly. This observation of interference fringes in a
macroscopic mechanical resonator opens an avenue for several further studies including the
exploration of potential quantum gravitational phenomena, and the development of quantum
metrology and sensing applications.
[1] M. Ringbauer, T. J. Weinhold, A. G. White, M. R. Vanner arXiv:1602.05955 (2016).
Combining 1D Nanoscale Waveguides and Cold Atoms
Neil Corzo, Laboratoire Kastler Brossel
Abstract: Reversible light-matter interfaces are crucial elements in quantum optics and
quantum information networks. In this context, our group focuses on the manipulation of light
at the single-photon level using ensembles of cold neutral atoms. In a free-space
implementation, we reported for instance the quantum storage of qubits encoded in the
orbital angular momentum degree of freedom [1] and a multiple-degree-of-freedom quantum
memory for structured light [2]. Recently, our group has also developed an interface where
light, tightly guided by a subwavelength-diameter optical fiber, strongly interacts with free or
trapped atoms near its vicinity. Here, I will describe two of our more recent results using this
interface: a) the demonstration of slow light and optical storage at the single-photon level in
this all-fibered setting [3]; and b) the observation of a large Bragg reflection off a 1D optical
lattice [4]. Our atom-fiber interface, with its enhanced atom-photon interactions, constitutes a
promising alternative to free-space focusing, which limits the interaction one can obtain, and
provides a novel platform for developing all-fibered quantum networks.
[1] A. Nicolas et al., A quantum memory for orbital angular momentum photonic qubits,
Nature Photon. 8, 234 (2014).
[2] V. Parigi et al., Storage and retrieval of vector beams of light in a multiple-degree-offreedom quantum memory, Nature Commun. 6, 7706 (2015).
[3] B. Gouraud et al., Demonstration of a memory for tightly guided light in an optical
nanofiber, Phys. Rev. Lett. 114, 180503 (2015).
[4] N. Corzo et al., Large Bragg reflection from a 1D chains of trapped atoms near a
nanoscale waveguide, in preparation.
36
Random symmetric states for robust quantum metrology
Michal Oszmaniec, ICFO (Barcelona)
Abstract: We study how useful random states are for quantum metrology, i.e., surpass the
classical limits imposed on precision in the canonical phase estimation scenario.
First, we prove that random pure states drawn from the Hilbert space of distinguishable
particles typically do not lead to super-classical scaling of precision even when allowing for
local unitary optimization.
Conversely, we show that random states from the symmetric subspace typically achieve the
optimal Heisenberg scaling without the need for local unitary optimization.
Surprisingly, the Heisenberg scaling is observed for states of arbitrarily low purity and
preserved under finite particle losses. Moreover, we prove that for such states a
standard photon-counting interferometric measurement suffices to typically achieve the
Heisenberg scaling of precision for all possible values of the phase at the same time.
Finally, we demonstrate that metrologically useful states can be prepared with short random
optical circuits generated from three types of beam-splitters and a non-linear (Kerr-like)
transformation.
The full version of the work can be found on arXiv:1602.05407
Determining the essential components of a quantum many-body system from
experiment
Jörg Schmiedmayer, TU-Wien
Abstract: A central objective of quantum simulators is to capture the essential physics of
complex quantum many-body systems from experimental observations. We experimentally
study a pair of tunnel-coupled one-dimensional atomic superfluids, which realise the
quantum sine-Gordon model. From measured interference patterns we extract phase
correlation functions and analyse if, and under which conditions, the higher-order correlation
functions factorise into lower ones. This allows us to characterise the essential features of
the model solely from our experimental measurements, detecting the relevant quasiparticles,
their interactions and the topologically distinct vacua. Our method provides comprehensive
insights into a non-trivial quantum field theory and establishes a general method to analyse
quantum many-body systems through experiments.
Undoing the effect of loss on entanglement
Tim Ralph, University of Queensland
Abstract: We present experimental results in which a two-mode squeezed state that has
been corrupted by a large amount of loss on one mode is recovered via distillation. The level
of entanglement in our distilled state is higher than that achievable by direct transmission of
any state through a similar loss channel. This is a key bench-marking step towards the
realisation of a practical continuous-variable quantum repeater and other CV quantum
protocols.
37
Experimental realisation of a variational ground state solver on a photonic chip
Jianwei Wang, University of Bristol
Abstract: We report an experimental implementation of a new hybrid protocol for solving
eigenproblems using a quantum photonic processor and a classical searching algorithm.
This protocol estimates the ground state energy of a quantum system by combining ideas
from phase estimation and variational eigensolvers. Specifically, it learns this energy via
direct measurement of only one qubit and then applies a variational optimisation of the trial
state to estimate the minimal energy. We use this protocol to infer the ground state for the
exciton transfer Hamiltonian in chlorophyll on a reconfigurable silicon quantum photonic
device that can implement non-compiled controlled unitary operations.
Distinguishability in three-photon scattering
Stefanie Barz, University of Oxford
Abstract: When more than two particles are involved, interference takes on a surprisingly
rich character, which extends beyond the pairwise distinguishabilities.
In fact, the output statistics from three interfering photons depends on four real parameters.
Here, we show how the full parameter space can be probed experimentally by generating
heralded single photons in three independent photon sources and interfering them in a fibre
tritter. The full coincidence landscape is accessed by exploiting multiple degrees of freedom:
time delays and polarisation.
AlGaAs photonic devices: from
communications
Sara Ducci, Paris Diderot University
quantum
state
generation
to
quantum
Abstract: Nonclassical states of light are key components in quantum information science; in
this domain, the maturity of semiconductor technology offers a huge potential in terms of
ultra-compact devices including the generation, manipulation and detection of many
quantum bits. Here we present our last achievements on AlGaAs quantum photonic devices
emitting non-classical states of light at room temperature via spontaneaous parametric down
conversion; the choice of this platform combines the advantages of a mature fabrication
technology, photon pair emission in the C-telecom band, a direct band-gap and a high
electro-optics effect. Here we show how microcavities based on a transverse pump
configuration generating counterpropagating photons display an exterme versatility to
engineer frequency correlations between the two photons of the pair. A toolbox to engineer
and measure continuous variable entanglement leading to the production of Schrodinger
cats and compass states will be presented. On the other hand, devices based on modal
phase matching allow to achieve an extreme compactness, having already led to electrically
injected photon pair sources working at room temperature. The quality of the quantum state
generated by our devices will be caracterized in terms of indistinguishability and level of
entanglement between the photons. In the last part of the talk, we will present our last results
on a simple and complete system based on our source and on standard telecom
components to perform a multi-user distribution of quantum keys based on polarization
entangled photons.
38
Separability Revisited
Maciej Lewenstein, ICFO
Abstract: Although assessing entanglement for generic multipartite states is recognized to be
a very difficult task there might be tractable ways when the states under scrutiny fulfill some
symmetries. Here we revisited the separability problem of general Diagonal Symmetric
states, showing that they display a non trivial and rich structure, linked to their non-locality
properties.
Quantum Information Processing with Trapped Ions and Photons
Rainer Blatt, Universatität Innsbruck
Abstract: In this talk, the basic toolbox of the Innsbruck quantum information processor
based on a string of trapped Ca+ ions will be reviewed. For quantum information processing,
the toolbox operations are employed for quantum computations [1], for quantum simulations
[2], and with optical cavities and photons they are used for the implementation of quantum
interfaces [3] for the realization of quantum networks.
For quantum computation, a scalable Shor algorithm was realized [1] with a string of trapped
Ca+ ions. Towards scaling the trapped ion quantum computer, we encode one logical qubit
in entangled states distributed over seven trapped-ion qubits. We demonstrate the capability
of the code to detect one bit flip, phase flip or a combined error of both, regardless on which
of the qubits they occur. Furthermore, we apply combinations of the entire set of logical
single-qubit Clifford gates on the encoded qubit to explore its computational capabilities [4].
The quantum toolbox is further applied to carry out both analog and digital quantum
simulations. The basic simulation procedure will be presented and its application will be
discussed for a variety of spin Hamiltonians. Moreover, a spectroscopic technique is
presented to study artificial quantum matter and use it for characterizing quasiparticles in a
many-body system of trapped atomic ions [5]. For the realization of a quantum interface,
trapped Ca+ ions in a cavity QED setup allow entanglement of a qubit with a photon and
quantum state mapping [3].
[1] T. Monz et al., Science 351, 1068 (2016).
[2] P. Jurcevic et al., Nature 511, 202 (2014).
[3] T. Northup and R. Blatt, Nature Photonics 8, 356 (2014).
[4] D. Nigg et al., Science 345, 302 (2014).
[5] P. Jurcevic et al., Phys. Rev. Lett. 115, 100501 (2015).
Programmable integrated optical circulator controlled by a single spin-polarized atom
Arno Rauschenbeutel, TU Wien - Atominstitut, Vienna, Austria
Abstract: We realize an integrated optical circulator which is based on the chiral interaction
of a single atom with a pair of whispering-gallery-modes in a silica bottle microresonator. The
strong transverse confinement of these modes leads to an inherent link between the local
polarization of the light and its sense of propagation in the resonator, clockwise or counterclockwise. In conjunction with the strongly polarization-dependent transition strengths of
spin-polarized rubidium 85 atoms, this allows us to implement a direction-dependent atomlight interaction: For the clockwise propagating mode, we reach the strong coupling regime,
while the coupling between the counter-clockwise mode and the atom is negligible.
Interfacing this nonreciprocal atom-cavity system with two tapered fiber couplers in add-drop
configuration thus implements an optical circulator. We study the device performance and
39
show that the spin state of the atom controls to which output ports the light is routed. The
demonstrated circulator is compatible with ultra-low light levels down to single photons and
can, in principle, be operated in a quantum superposition of different routing directions. It
thereby constitutes a first example of a new class of nonreciprocal quantum devices with
many potential applications in integrated optical quantum networks and circuits.
Creating perfect single photons for the demonstration of quantum supremacy
Chao-Yang Lu, University of Science and Technology of China, Hefei
Abstract: In this talk, I will report two routes towards experimental boson sampling with many
photons. One is based on spontaneous parametric down-converted (SPDC) photon pairs
that are generated probabilistically. Exploiting scattershot boson sampling scheme, the
probabilistic nature of SPDC can be overcome by using ~n^2 SPDC sources. The other,
more direct, route is employing deterministically generated single photons from solid-state
quantum emitters. To reach boson sampling to a scale of 20-30 photons, both approaches
would need single photons (heralded or deterministically generated) with simultaneously
high purity, efficiency, and indistinguishability. This criteria was, however, not fulfilled
previously, and thus, boson sampling with SPDC was limited to 3 photons for arbitrary input
configuration and quantum dot (QD) single photons was limited to 2-photon experiments in
the past 15 years since the first observation of antibunching. We developed SPDC twophoton source with simultaneously a brightness of ~12 MHz/W, a collection efficiency of
~70% and an indistinguishability of ~91% between independent photons. With this, we
demonstrate genuine and distillable entanglement of ten photons under different pump
power [1]. Such a state-of-the-art multi-photon platform will provide enabling technologies for
challenging optical quantum information tasks such as teleportation of three degrees of
freedom of photons [2] and scattershot boson sampling. Self-assembled InGaAs QDs are
promising solid-state emitters with near-unity quantum efficiency and fast decay rate. Using
a QD coupled to a micropillar, we produced single photons with high purity, near-unity
indistinguishability [3], and high extraction efficiency, compatibly and simultaneously [4].
Long streams of >1000 single photons separated by tens of microseconds maintain a >92%
indistinguishability, which are shown to be near transform limit [5]. The single photons are
time-bin encoded and interfered in an electrically programmable loop-based network [6].
With further refinement, the two approaches may be feasible to be scaled up to ≳ 20-boson
sampling to outperform classical computers, and thus provide experimental evidence against
the Extended Church-Turing Thesis.
References:
[1] X.-L. Wang et al. Experimental ten-photon entanglement, arXiv:1605.08547.
[2] X.-L. Wang et al. Quantum teleportation of multiple degrees of freedom of a single
photon, Nature 518, 516 (2015).
[3] Y.-M. He et al. On-demand semiconductor single-photon source with near-unity
indistinguishability Nature Nanotechnology 8, 213 (2013).
[4] X. Ding et al. On-demand single photons with high extraction efficiency and near-unity
indistinguishability from a resonantly driven quantum dot in a micropillar, Phys. Rev. Lett.
116, 020401 (2016).
[5] H. Wang et al. Near transform-limited single photons from an efficient solid-state quantum
emitter, Phys. Rev. Lett. 116, 213601 (2016).
[6] Y. He et al. Boson sampling with a single-photon device, arXiv:1603.04127
40
Longitudinal Coupling: Key to Scalable Qubit Layouts?
David DiVincenzo, RWTH Aachen University
Abstract: Many labs presently plan to scale up to the next generation of quantum computing
systems (10-100 qubits) usings arrays of coupled qubit-cavity systems, with the coupling
being described by the Jaynes-Cummings Hamiltonian. But this coupling is not ideal for
scaleup; we have worked out constructions, feasible within circuit QED, for a new fixedfrequency superconducting qubit and show how it can be scaled up to a grid with strictly
local interactions, where interactions involve longitudinal rather than transverse (JaynesCummings) couplings. This longitudinal coupling is inherently different from the usual σxtype \textit{transverse coupling}even with always-on interactions; couplings produce dressed
qubits, but the range of dressing extends strictly to the nearest-neighbor resonator and no
further. We note that just four distinct resonator frequencies, and only a single unique qubit
frequency, suffice for the scalability of this scheme. Details of this work are found in
arxiv:1511.06138.
41
Abstracts – Posters (Monday)
P1-3 Entanglement measure for composite systems of indistinguishable particles
Janusz Grabowski
Abstract: We analyze the concept of entanglement for multipartite system with bosonic and
fermionic constituents and its generalization to systems with arbitrary parastatistics. We use
the representation theory of symmetric groups to formulate a unified approach to this
problem in terms of simple tensors with appropriate symmetry which turn out to be highest
weight vectors of the natural representation of the symmetric group. For an arbitrary
parastatistics, we define the S-rank generalizing the notion of the Schmidt rank. The S-rank,
defined for all types of tensors, serves for distinguishing entanglement of pure states and
constructing an entanglement measure on mixed states, satisfying all standard
requirements.
P1-4 Heralded Measurement-Device-Independent Quantum Key Distribution with
Vector Vortex Beams
Chen Dong, Shang-Hong Zhao and Shutao Li
Abstract: The vector vortex(VV) beam, originally introduced to exhibit a form of single
particle quantum entanglement between different degrees of freedom, has specific
applications for quantum-information protocols. In this paper, by combining measurementdevice-independent quantum key distribution (MDI-QKD) with spontaneous parametricdown-conversion source(SPDCS), we present a modified MDI-QKD scheme with pairs of VV
beams, which shows a structure of hybrid entangled entanglement corresponding to
intrasystem entanglement and intersystem entanglement. The former entanglement, which is
entangled between polarization and orbit angular momentum within each VV beam, is
adopted to overcome the polarization misalignment associated with random rotations in
quantum key distribution. The latter entanglement, which is entangled between the two VV
beams, is used to perform MDI-QKD protocol with SPDCS to inherit the merit of heralded
process. The numerical simulations show that our modified scheme has apparent advances
both in transmission distance and key generation rate compared to the original MDI-QKD.
Furthermore, our modified protocol only needs to insert q-plates in practical experiment.
P1-5 Quantum Coherence Sets The Quantum Speed Limit For Mixed States
Debasis Mondal, Chandan Datta and Sk Sazim
Abstract: We cast observable measure of quantum coherence or asymmetry as a resource
to control the quantum speed limit (QSL) for unitary evolutions. For non-unitary evolutions,
QSL depends on that of the state of the system and environment together. We show that the
product of the time bound and the coherence (asymmetry) or the quantum part of the
uncertainty behaves in a geometric way under partial elimination and classical mixing of
states. These relations give a new insight to the quantum speed limit. We also show that our
bound is experimentally measurable and is tighter than various existing bounds in the
literature.
http://www.sciencedirect.com/science/article/pii/S0375960115010518
42
P1-7 Pushing single photon counting technology towards better Size, Weight and
Power (SWAP) performance.
Rakhitha Chandrasekara, Zhongkan Tang, Yue Chuan Tan, Kadir Durak, Cliff Cheng and
Alexander Ling
Abstract: Single photon counting is widely used in low-light sensing and communications
experiments. However, the development of detector technology often does not keep pace
with the development of new optical sources or protocols, restricting the deployment of
quantum communication infrastructure. Our team is working on a number of quantum
experiments where the Size, Weight and Power (SWAP) requirements are too challenging
for commercial-off-the-shelf detector modules and necessitate the development of fast,
compact and efficient detector
circuits. In this poster, we present a novel in-situ measurement method that extracts the
pulse height from silicon Geiger-mode avalanche photodiodes (GM-APDs) while it is
performing photon counting. This technique will enable fine control of the GM-APD when it is
actively quenched, and enable a compact and efficient detector circuit that is capable of
detecting millions of photon events per second. We also consider the interplay of photon
statistics (from a single photon source) and detector circuit response in order to develop a
model that predicts the performance of a quantum communication system based on
entangled photons from Spontaneous Parametric Downconversion sources.
P1-8 Temporal imaging with squeezed light
Mikhail Kolobov and Giuseppe Patera
Abstract: We generalize the scheme of conventional temporal imaging to quantum temporal
imaging viable for nonclassical states of light. As an example, we apply our scheme to
temporally broadband squeezed light and demonstrate a possibility of its noiseless
magnification. In particular, we show that on can magnify by a given factor the coherence
time of squeezed light and match it to the response time of the photodetector. This feature
opens new possibilities for practical applications of temporally broadband squeezed light in
quantum optics and quantum information.
P1-10 Quantum key distribution with leaky devices
Marcos Curty, Kiyoshi Tamaki and Marco Lucamarini.
Abstract: In recent years, there has been a great effort to prove the security of quantum key
distribution (QKD) with a minimum number of assumptions. Besides its intrinsic theoretical
interest, this would allow for larger tolerance against device imperfections in the actual
implementations. However, even in this device-independent scenario, one assumption
seems unavoidable, that is, the presence of a protected space devoid of any unwanted
information leakage in which the legitimate parties can privately generate, process and store
their classical data. Here we relax
this unrealistic and hardly feasible assumption and introduce a general formalism to tackle
the information leakage problem in QKD systems. We apply our security proof to cases of
practical interest and show key rates similar to those obtained in a perfectly shielded
environment. Our work constitutes a fundamental step forward in guaranteeing
implementation security of quantum communication systems.
43
P1-11 Survivor! Analysis of a photon pair source recovered intact from a catastropic
launch failure.
Tang Zhongkan Xavier, Alexander Ling, Rakhitha Chandrasekara, Yue Chuan Tan and Cliff
Cheng
Abstract: Secure generation of symmetric key material at distant sites using quantum
signals, known as quantum key distribution (QKD), is one of the most technologically mature
outcomes of research into quantum communication. Several efforts are ongoing to utilize
satellites as receivers or transmitters for QKD demonstrations in order to overcome the
distance limit due to the fiber losses and the lack of quantum repeaters. Motivated by the
vision of a global quantum communication network, we present a compact and rugged
photon pair source that can be embedded into small cost-effective satellites called
CubeSats.
One of the driving requirements to utilize CubeSats for this purpose is to build a photon pair
source that is compatible with the size, weight and power (SWaP) requirements of a
nanosatellite. The complete package (photon pair source and the electronics) was compact
(9.5 × 9.6 x 3.8 cm^3) with a mass of about 250 g and was designed to fit a standard
CubeSat spacecraft. The package was installed into GomX-2 CubeSat to be deployed from
International Space Station. Unfortunately the mission failed when the launch vehicle was
destroyed shortly after launch but GomX-2 was successfully recovered from the debris. The
science package within was found to be completely operational, continuing to produce high
quality polarization correlations. Post-recovery data is compared to baseline measurements
collected before the launch attempt and no degradation in brightness or polarization
correlation was observed.
In this talk, we will discuss the steps taken in assembling the source, discuss how possible
points of failure can be addressed in future designs, and describe future missions that are in
the pipeline. The ability of the source to survive very dramatic conditions yields lessons for
designers of practical quantum technology. It demonstrates that with adequate engineering
quantum devices need not be delicate instruments confined to laboratory environments. Our
work leverages the on-going revolution in small satellite systems and demonstrates that the
financial and technical barriers to quantum experiments in space are rapidly falling.
P1-12 Semiclassical Theory of Superresolution for Two Incoherent Optical Point
Sources
Mankei Tsang, Ranjith Nair and Xiao-Ming Lu
Abstract: Using a semiclassical model of photodetection with Poissonian noise and insights
from quantum metrology, we prove that linear optics and photon counting can optimally
estimate the separation between two incoherent point sources without regard to Rayleigh's
criterion. The model is applicable to weak thermal or fluorescent sources as well as lasers.
44
P1-13 Quantum State Smoothing
Howard Wiseman and Ivonne Guevara
Abstract: Smoothing is an estimation method whereby a classical state (probability
distribution for classical variables) at a given time is conditioned on all-time (both earlier and
later) observations. Here we define a smoothed quantum state for a partially monitored open
quantum system, conditioned on an all-time monitoring-derived record. We calculate the
smoothed distribution for a hypothetical unobserved record which, when added to the real
record, would complete the monitoring, yielding a pure-state ``quantum trajectory''.
Averaging the pure state over this smoothed distribution yields the smoothed quantum state.
This is a mixed state, but, we show, less mixed than the conventional (filtered) state
conditioned only on the past record. We distinguish our quantum smoothed state from other
concepts that have been studied recently, and show how the choice of actual unravelling
affects the purity increase over that of the filtered state.
P1-15 Electronic and spin properties of Si vacancy in SiC
Moein Najafi Ivaki and Mohammad Ali Vesaghi
Abstract: The silicon vacancy in silicon carbide is a strong emergent candidate for
applications in quantum information processing and sensing. Alongside research focusing on
nitrogen vacancy centers in diamond, an alternative strategy seeks to identify new spin
systems with an expanded set of technological capabilities. 4H, 6H and 3C polytypes of SiC
all host coherent and optically addressable defect spin states, including states in all three
with room-temperature quantum coherence.
Electron paramagnetic resonance (EPR) and optically detected magnetic resonance
(ODMR) investigations suggest that silicon vacancy related point defects in SiC possess
properties the similar to those of the NV center in diamond, which in turn makes the silicon
vacancy in silicon carbide a strong emergent candidate for applications in quantum
information processing and sensing.
We are seeking to provide a new theoretical frame to explain a wider range of experimental
results. Employing a proposed generalized Hubbard model, with the help of electronic
structure programs, DFT, second quantization, and various computational approaches, we
are bring about new insight on this special vacancy.
Our central point of attention is folding in two main approaches for finding Hubbard
parameters as well as wave functions: SP3 orbitals and DFT. To obtain electronic and spin
properties of the system, we combine these two, taking into account all the governing
interactions and possibilities for the system to relax itself. The properties may include: spatial
symmetries, ground and excited states spin, Spin densities, entanglement, and transition
energy of optical transition.
P1-17 Optimal two-mode attack against two-way continuous-variable quantum key
distribution
Yichen Zhang, Zhengyu Li, Yijia Zhao, Song Yu and Hong Guo
Abstract: We report the optimal eavesdropping strategy against two-way continuous-variable
quantum key distribution at fixed channel parameters, which is given by a two-mode attack
with symmetric and appropriate separable correlations.
45
P1-18 Measurement-based Formulation of Quantum Heat Engine
Masahito Hayashi and Hiroyasu Tajima
Abstract: There exist two formulations for quantum heat engine. One is semi-classical
scenario, and the other is full quantum scenario. The former is formulated as a unitary
evolution for the internal system, and is adopted by the community of statistical mechanics.
In the latter, the whole process is formulated as unitary. It was adopted by the community of
quantum information. However, their formulation does not consider measurement process.
In particular, the former formulation does not work when the amount of extracted work is
observed.
In this paper, we formulate the quantum heat engine as the measurement process because
the amount of extracted work should be observed in a practical situation. Then, we clarify the
contradiction of the former formulation by using a novel trade-off relation. The trade-off
relation clarifies the impossibility of proper work extraction by an internal unitary process.
P1-19 Development of single photon source using Silicon-Vacancy(SiV) nanodiamond
Hong Kee Suk, Bae In-Ho and Lee Dong-Hoon
Abstract: The single photon source(SPS) using impurity centers in nano-diamonds, in
specific nitrogen-vacancy(NV) and silicon-vacancy (SiV) centers is becoming a promising
qubit for quantum metrology and communications. As the single emitter, impurity center of
silicon-vacancy (SiV) in a nano-diamond is investigated. In this conference, we present the
current status and results of the development of the single photon source at KRISS.
P1-21 Inhibition of ground-state superradiance and light-matter decoupling in circuit
QED
Zeliang Xiang, Tuomas Jaako and Peter Rabl
Abstract: We study effective light-matter interactions in a circuit QED system consisting of a
single LC resonator, which is coupled symmetrically to multiple superconducting qubits.
Starting from a min- imal circuit model, we demonstrate that in addition to the usual
collective qubit-photon coupling the resulting Hamiltonian contains direct qubit-qubit
interactions, which prevent the otherwise ex- pected superradiant phase transition in the
ground state of this system. Moreover, these qubit-qubit interactions are responsible for an
opposite mechanism, which at very strong couplings completely decouples the photon mode
and projects the qubits into a highly entangled ground state. These findings shed new light
on the controversy over the existence of superradiant phase transitions in cavity and circuit
QED systems, and show that the physics of ultrastrong light-matter interactions in two- or
multi-qubit settings differ drastically from the more familiar one qubit case.
46
P1-22 Steering Bell-diagonal states (Ref. www.nature.com/articles/srep22025)
Quan Quan
Abstract: We investigate the steerability of two-qubit Bell-diagonal states under projective
measurements by the steering party. In the simplest nontrivial scenario of two projective
measurements, we solve this problem completely by virtue of the connection between the
steering problem and the joint-measurement problem. A necessary and sufficient criterion is
derived together with a simple geometrical interpretation. Our study shows that a Belldiagonal state is steerable by two projective measurements iff it violates the Clauser-HorneShimony-Holt (CHSH)
inequality, in sharp contrast with the strict hierarchy expected between steering and Bell
nonlocality. We also introduce a steering measure and clarify its connections with
concurrence and the volume of the steering ellipsoid. In particular, we determine the
maximal concurrence and ellipsoid volume of Bell-diagonal states that are not steerable by
two projective measurements. Finally, we explore the steerability of Bell-diagonal states
under three projective measurements. A simple sufficient criterion is derived, which can
detect the steerability of many states that are not steerable by two projective measurements.
Our study provided a number of instructive analytical results on steering, which are quite
rare in the literature. These results not only furnish a simple geometric picture about steering
of Bell-diagonal states, but also offer valuable insight on the relations between
entanglement, steering, and Bell nonlocality. They may serve as a starting point for exploring
more complicated steering scenarios.
P1-23 Suppression law of quantum states in a 3D photonic fast Fourier transform chip
Niko Viggianiello
Abstract: During the last three decades, photonic platforms have been demonstrated to be in
principle capable to perform universal quantum computing.
Recently, multi-particle interference effects of many photons in large interferometers are
attracting a strong interest, as they should be able to show unprecedented evidences of the
superior quantum computational power compared with that of classical devices. The main
example is given by the boson sampling computational problem, which consists in sampling
from the probability distribution given by the permanents of the nxn submatrices of a given
Haar random unitary. The problem is computationally hard (in n) for a classical computer,
since calculating the permanent of a complex-valued matrix is a #P hard problem. However,
sampling from the output distribution can be efficiently achieved by letting n indistinguishable
photons evolve through an optical interferometer implementing the unitary transformation in
the Fock space, and by detecting output states. The chance to provide evidences of a postclassical computation with this relatively simple set-up has triggered a large experimental
effort, leading to small-scale implementations, as well as theoretical analyses on the effects
of experimental imperfections and on possible implementations including alternative
schemes.
In the context of searching for experimental evidences, a boson sampling experiment poses
a problem of certification of the result’s correctness in the computationally hard regime. The
very complexity of the boson-sampling computational problem precludes the use of a bruteforce approach, that is, calculating the expected probability distribution at the output and
comparing it with the collected data. Efficient statistical techniques able to rule out trivial
alternative distributions have been proposed and tested, but the need for more stringent
tests able to rule out less trivial distributions has led, and continues to encourage, additional
research efforts in this direction. In particular, an efficient test able to confirm true n-photon
interference in a multimode device has been recently proposed. The protocol is based on the
use of an interferometer implementing the Fourier matrix. When feeding this device with
multi-photon states of a specific symmetry, suppression of many output configurations is
47
observed, due to granular many-particle interference. The implications of this effect go well
beyond the certification of boson sampling devices. As a generalization of the twophoton/two-modes Hong–Ou–Mandel (HOM) effect, the suppression law, also named ZeroTransmission law, is important at a fundamental level, while at the practical level it could be
used as a diagnostic tool for a wide range of photonic platforms.
We report the experimental observation of the recent theoretically proposed suppression law
for Fourier matrices, and its use to validate quantum many-body interference against
alternative non-trivial hypotheses resulting in similar output probability distributions. The
Fourier matrices have been implemented with an efficient and reliable approach by
exploiting the quantum version of the fast Fourier Transfprm. The unitariy is implemented in
integrated interferometers by exploiting the three-dimensional (3D) capabilities of
femtosecond laser writing, so adopting an architecture scalable to a larger number of modes.
The peculiar behaviour of Fock states compared with other kinds of states is investigated,
showing in principle the validity of the certification protocol for the identification of true
granular n-particle interference, which is the source of a rich landscape of quantum effects
such as the computational complexity of boson sampling and can be a building block for a
well tested source for quantum simulation platforms.
P1-28 Quantum dot based simultaneous classical logic gates
Ronny A. Christin and Duncan L. MacFarlane
Abstract: The interaction with a “flying” photon traveling through a waveguide and a quantum
dot has been previously proposed as a way to create quantum photonic logic gates. We
propose a hybrid logic gate based on the interaction between a path encoded photon and
quantum dots coupled to the waveguides. In this work, the stimulated emission
characteristics of quantum dots are leveraged to enable logical operations such as the
NAND gate.
P1-29 Error probability in quantum-dot based quantum circuits
Ronny A. Christin and Duncan L. MacFarlane
Abstract: Quantum Dots have been investigated for various roles in quantum computing.
However, spontaneous emission results in the loss of quantum information. The lifetime, τ21,
and the speed of light in the waveguides determine the maximum physical dimensions of the
circuit for a given number of quantum dots and probability of information loss. Control,
therefore, over τ21 is critical to the realization of these circuits. This work details the Purcell
factors necessary to realize a circuit of any reasonable size.
48
P1-30 Measurement-dependent locality with non-i.i.d. measurements
Ernest Y.-Z. Tan, Yu Cai and Valerio Scarani
Abstract: For tests or applications of Bell inequalities, an important assumption is that the
measurements are chosen freely, or more specifically, that the choice of measurements is
independent of the source [1]. This can also be viewed in terms of randomness amplification,
where partially free random bits are used as inputs for the measurements and the
measurement outcomes are taken as output bits [2]. The consequences of relaxing the
assumption of measurement independence have been investigated in previous works [1,3],
indicating for instance that a relatively small amount of measurement dependence is
sufficient to model a violation of the CHSH inequality. On the other hand, Pütz and coworkers [3] showed that the set of correlations that can be modelled in this manner is
restricted to a set referred to as the measurement-dependent local (MDL) polytope. In
particular, they provided an MDL inequality for i.i.d. measurements that can be violated by
quantum correlations for arbitrarily small amounts of measurement independence.
In this work, we study the case of non-i.i.d. measurements, which may be correlated across
multiple runs of a Bell test. We focus mainly on the case of block-i.i.d. measurements with
blocks of size 2. We have found that the inequality developed for the i.i.d. case is
substantially less robust in this scenario, but also that there exist inequalities more suitable
for the block-i.i.d. case. However, we have found a nontrivial level of measurement
dependence beyond which the no-signalling polytope becomes a subset of the MDL blocki.i.d. polytope, and thus there can be no quantum violations of MDL block-i.i.d. inequalities
beyond this level. Therefore, this shows that the result for the i.i.d. scenario does not
generalise to the non-i.i.d. scenario.
[1] Hall, M. Relaxed Bell inequalities and Kochen-Specker theorems. Phys.
Rev. A 84, 022102 (2011).
[2] Colbeck, R. and Renner, R. Free randomness can be amplified. Nature Physics 8, 450–
453 (2012).
[3] Pütz, G., Rosset, D., Barnea, T. J., Liang, Y.-C., and Gisin, N.
Arbitrarily Small Amount of Measurement Independence Is Sufficient to Manifest Quantum
Nonlocality. Phys. Rev. Lett. 113, 190402 (2014).
P1-32 Weiss-Weinstein Error Bounds for Quantum Parameter Estimation
Xiao-Ming Lu and Mankei Tsang
Abstract: We propose a quantum version of the Weiss-Weinstein lower bounds on the
estimation error of random parameters. The quantum Weiss-Weinstein bounds (QWWB) is a
superior alternative to the popular quantum Cramer-Rao bound (QCRB), in the sense that it
includes the QCRB as a special case and does not require the differentiability of prior
distributions and conditional quantum states as the QCRB does.
49
P1-33 Quantum state preparation: the untold story
Holger F. Hofmann
Abstract: Quantum mechanics usually starts with the assumption that physical systems are
described by quantum states. However, the preparation of a system in a specific quantum
state is itself an actual physical process in the laboratory, and no discussion of quantum
measurement can be complete without a look at the actual physics of quantum state
preparation. Here, I present a general analysis of the state preparation process that
identifies dynamical randomizations as the central characteristics of all quantum state
preparation processes. I point out that this result provides a physical explanation for the
mathematical formalism that may resolve many of the mysteries of quantum mechanics.
P1-34 Multi-photon interference explained by the action of optical phase shifts
Holger F. Hofmann, Keito Hibino, Kazuya Fujiwara and Jun-Yi Wu
Abstract: Multi-photon interferences are described by superpositions of different photon
numbers in the paths of the interferometer. But what determines the periodicity of a specific
interference fringe when the input state and the detected state are superpositions of a wide
range of path states? Here, we show that the periodicity of a multi-photon fringe is a function
of the input and output photon numbers that corresponds to the classical relation between
intensity differences in the interferometer.
P1-35 Atoms as quantum beam-splitters in waveguide QED
Alexandre Roulet, Pierre-Olivier Guimond, Jibo Dai, Huy Nguyen Le and Valerio Scarani
Abstract: Rapid experimental progress is being made in the field of waveguide QED. This
provides an interesting playground for studying what happens when devices that are usually
considered classical are replaced by quantum objects allegedly performing the same
functionality. In this paper we present the following three devices:
• an atomic beam-splitter;
• a cavity made of atomic Bragg mirrors;
• a diode based on two non-identical atoms.
Please refer to the attached abstract for further details on our submission.
P1-36 Robust H∞ Estimation for Linear Uncertain Quantum Systems
Shibdas Roy and Ian Petersen
Abstract: We consider classical estimators for a class of physically realizable linear quantum
systems. Optimal estimation using a complex Kalman filter for this problem has been
previously explored. Here, we study robust H∞ estimation for uncertain linear quantum
systems. The estimation problem is solved by converting it to a suitably scaled H∞ control
problem. The solution is obtained in the form of two complex algebraic Riccati equations. A
relevant example involving dynamic optical squeezers is presented to illustrate the efficacy
of our method.
50
P1-37 Two qubit near-field microwave gates on 43Ca+
James Tarlton, Martin Sepiol, Jochen Wolf, Thomas Harty, Christopher Ballance, Diana
Craik, Vera Schafer, Keshav Thirumalai, Laurent Stephenson, Andrew Steane and David
Lucas
Abstract: Quantum logic with trapped atomic ions relies on coupling the ions via their shared
motional modes. This coupling is provided by the gradient of a driving field over the extent of
the ions’ motion. This driving field has traditionally been produced by lasers because of the
favorable short wavelengths that can be used. However, when ions are confined tens of
microns above a waveguide, strong magnetic field gradients can be generated at microwave
frequencies despite their long free-space wavelength [1].
Compared with lasers, this approach promises a higher level of control and integration,
along with a reduction of technical complexity thanks to the relative ease of generating and
manipulating microwave fields. So far, this method has only been applied at the National
Institute of Standards and Technology, resulting in a two qubit gate fidelity of 76% [2].
We present our research on this technique using an in-house designed and micro-fabricated
surface ion trap at room temperature. We have been able to implement a two qubit MølmerSørensen gate on two 43Ca+ ions in a static field of 146G with 99.3% fidelity, above the
fault-tolerant threshold.
We also present our work towards developing a new trap with two major technical
improvements. The first of these is to produce a microwave field gradient at an approximate
field null with a single "meander" electrode, as proposed by the Hannover group [3]. The
second improvement is to cryogenically cool the trap, which should reduce the ion heating
rate [4,5], one of the main sources of gate error in our current system.
References
[1] C. Ospelkaus et al., Physical Review Letters 101, 090502 (2008)
[2] C. Ospelkaus et al., Nature 476, 181-184 (2011)
[3] M. Carsjens et al., Applied Physics B 114, 243-250 (2014)
[4] J. Labaziewicz et al., Physical Review Letters 101, 180602 (2008)
[5] J. Chiaverini et al., Physical Review A 89, 012318 (2014)
P1-39 Protecting quantum discord from amplitude damping decoherence via weak
measurement and its reversal
Yong-Su Kim, Jiwon Yune, Kang-Hee Hong, Hyang-Tag Lim, Jong-Chan Lee, Osung Kwon,
Sang-Wook Han, Sung Moon and Yoon-Ho Kim
Abstract: We show that a protocol deploying weak measurement and quantum measurement
reversal can effectively protect quantum discord from amplitude damping decoherence, and
thus enabling to distribute quantum correlation between two remote parties in a noisy
environment. We theoretically and experimentally evaluate the effectiveness of quantum
measurement reversal in protecting the amount of quantum discord. Our results ultimately
verifies that general quantum correlations can be protected by the protocol.
51
P1-40 Experimental demonstration of efficient superdense coding in the presence of
non-Markovian noise
Bi-Heng Liu, Xiao-Min Hu, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, Sabrina
Maniscalco and Jyrki Piilo
Abstract: Many quantum information tasks rely on entanglement, which is used as a
resource, for example, to enable efficient and secure communication. Typically, noise,
accompanied by loss of entanglement, reduces the efficiency of quantum protocols. We
demonstrate experimentally a superdense coding scheme with noise, where the decrease of
entanglement in Alice’s encoding state does not reduce the efficiency of the information
transmission. Having almost fully dephased classical two-photon
polarization state at the time of encoding, we reach values of mutual information close to
1.43 (1.73) with 3-state (4-state) encoding. This high efficiency relies both on non-Markovian
features, that Bob exploits just before his Bell-state measurement, and on very high visibility
(99.6%) of the Hong-Ou-Mandel interference within the experimental set-up. Our proof-ofprinciple results pave the way for exploiting non-Markovianity to improve the efficiency of
quantum information processing tasks.
P1-41 An analysis of the statistics of multi-photon interference
Kazuya Fujiwara and Holger F. Hofmann
Abstract: As total photon number increases, the interference of photon number states at a
50:50 beam splitter results in increasingly complex quantum interference patterns in the
probability distribution over possible output photon numbers. In this presentation, we analyze
the quantum interference patterns of the output for arbitrary photon numbers and derive a
simple relation that explains the appearance of periodic oscillations of probability in the
output photon number difference.
P1-43 Phase-encoded measurement device independent quantum key distribution
without a shared reference frame
Ying Sun and Shang-Hong Zhao
Abstract: In this paper, a phase-encoded measurement device independent quantum key
distribution (MDI-QKD) without a shared reference frame, which can generate secure keys
between two parties while the quantum channel or interferometer introduces an unknown
and slowly time-varying phase, is presented. Taking finite-key analysis into account, the
asymptotic secret key rate and error rate, respectively, with single photons source (SPS) and
weak coherent source (WCS), is analyzed. The numerical simulation show that the improved
phase-encoded MDI-QKD has apparent superiority both in transmission distance and key
generation rate, and the robustness and practical security will be greatly improved in the
high-speed MDI-QKD system, while the fluctuations of the secure key rate are primarily due
to the low systematic repetition rate. Moreover, the rejection of the frame-calibrating part will
intrinsically reduce the consumption of resources as well as the potential security flaws of
practical MDI systems. The analysis results indicate the feasibility of our scheme and its
value for QKD network scenarios.
52
P1-44 Unitary Estimation with Resource Constraints
Masahito Hayashi, Sai Vinjanampathy and Leong Chuan Kwek
Abstract: This paper addresses the estimation of the unknown phase parameter. Our
problem is composed of the optimization of the input state and the measurement. We
impose the energy constraint to the input state when the Hamiltonian is given as the number
operator in the Boson-Fock space. Then, we show that quadratic enhancement in the mean
squared error of the estimated parameter when the energy is sufficiently large. We propose
an experimental setup to generate an input state achieving for enhanced metrology using
squeezing transformations.
P1-45 Experimental Tests of Gravitational Decoherence
Nathan Mcmahon and Gerard Milburn
Abstract: Quantum mechanics and general relativity are two major achievements in physics,
both tested to high levels of accuracy. However as the theory currently stands these two
ideas are fundmentally incompatible. While understanding the full theory is a significant
project, taking the Newtonian limit we can begin to test gravitional interactions within the
quantum regime. There has been some interest in a class of models, such as the Penrose
and Diosi models [1,2], where gravitional interactions cause spontaneous collapse. More
recently the approach taken by Kefri, Taylor and Milburn predicts the same amount of
decoherence from gravitational sources as the Diosi model, but is built off the initial
assumption that gravity can only interact via a classical channel[3]. This kind of model leads
to other interesting results such as in their initial and subsequent papers where the KTM
model appears to indicate that interactions via gravity can never generate entanglement[3,4].
If such a statement is true in general it would place a limit on what kind of quantum
technologies could be constructed. Such as in the recent proposal by Johnsson, Brennen,
and Twamley [5] for a the measurement of the gravitational field using superconducting
qubits. In this style of technology the entanglement used is generated by gravitational
interactions. If the KTM model is indeed the correct description of Newtonian quantum
gravity then this proposal would not be a feasible approach to emergent quantum
technologies This leads to significant testable differences between the original quantum
theory and these spontaneous collapse via gravitational interactions models. Considering
optomechanical systems, we find that gravitational decoherence appears as a pure
temperature shift in the bath modes. Therefore any signitures of decoherence would simply
appear as a external source of heating in any prior experiments not testing for gravitational
decoherence.
We have considered methods to distinguish the signiture of gravitaitional decoherence from
other sources of heating and will discuss proposals for experimental tests of gravitational
decoherence. In particular we will discuss a proposal for an experimental test for
gravitational decoherence, which appears to be feasible with current technologies.
[1] On gravity's role in quantum state reduction, Roger Penrose, General relativity and
Gravitation 28 (5):581-600, (1996).
[2] The gravity-related decoherence master equation from hybrid mechanics, Lajos Diosi,
J.Phys.Conf.Ser. 306 012006 -(9), (2011)
[3] A classical channel model for gravitational decoherence, D. Kafri, J.M. Taylor and G. J.
Milburn, New J. Physics 16, 065020, (2014).
[4] Bounds on quantum communication via Newtonian gravity, D. Kafri, G. J. Milburn, J. M.
Taylor, New J. Physics 17, 015006, (2015).
[5] Macroscopic superpositions and gravimetry with quantum magnetomechanics, MT
Johnsson, GK Brennen, J Twamley, arXiv:1412.6864, (2014).
53
P1-46 Time multiplexing toward indistinguishable and deterministic single-photon
generation
Fumihiro Kaneda and Paul Kwiat
Abstract: Photon-pair generation by spontaneous parametric downconversion (SPDC) or
spontaneous four-wave mixing (SFWM) has been widely used for creating two- and multipartite entangled states and heralded single-photon states. However, the probabilistic nature
of the photon-pair generation process is a key obstacle to scaling up QIP systems beyond
proof-of-principle experiments. We report on our recent efforts toward a periodic and
deterministic single-photon source by use of time multiplexing of a heralded single-photon
source pumped by periodic laser pulses. Our preliminary implementation of a multiplexed
source demonstrated substantially enhanced single-photon probabilities.
P1-48 All-­‐Semiconductor Quantum Repeater Device
Danny Kim, Andrey Kiselev, Richard Ross, Matthew Rakher, Cody Jones and Thaddeus
Ladd
Abstract: Long distance quantum communication requires the ability to transmit, buffer, and
process quantum information via nodes called quantum repeaters. Proposals for quantum
repeaters exist in many media including trapped ions, atomic gases, and superconducting
optomechanics. An all solid-state approach would be desirable for manufacturability,
scalability, and potentially superior performance. Here, we propose an all semiconductor
quantum optoelectronic device (see Fig 1) that interfaces an optically-active self-assembled
quantum dot molecule (QDM) and a gated-dot array (GDA). The QDM provides an optical
interface and the GDA provides the storage of the quantum bits. The device emits a spinentangled photon, where the spin entanglement is subsequently transferred from the QDM
to the GDA through capacitive coupling. The resulting resource is an emitted photon whose
polarization is entangled to the electron spins in the GDA. This device can potentially
operate at a clock cycle in excess of 100MHz, orders of magnitude faster than current
quantum repeater schemes. In this poster I will present an analysis of the device, its
operation, and also preliminary experimental data that supports the feasibility of this device.
Topics include the proposed device heterostructure, Poisson-Schrödinger simulations of the
device, and the entanglement transfer scheme. Experiments towards extending T2 times
with pulse shaping and exploring other material systems in which this device may be
realized will also be presented.
54
P1-49 Surface effects on the coherence of superconducting qubits
Yiwen Chu, Christopher Axline, Chen Wang, Teresa Brecht, Yvonne Gao, Luigi Frunzio,
Michel Devoret and Robert Schoelkopf
Abstract: Solid-state qubits that act as artificial atoms have many advantages over real
atoms or ions, such as engineerability, scalability, and the lack of need for trapping or
cooling schemes. However, their quantum coherence is generally degraded due to the
complex environment in which they reside. In particular, while high-quality, nearly flawless
bulk materials can be used in these qubits, the presence of surfaces inevitably introduces
imperfections. These surface effects are an important limiting factor in the performance of
solid state qubits ranging from nitrogen-vacancy centers in diamond to superconducting
Josephson-junction based devices. We study the decoherence of 3D transmon
superconducting qubits on sapphire and silicon and find that the lifetimes of these qubits are
limited by loss due to material interfaces. In the case of silicon, we demonstrate the use of
micromachining techniques to replace lossy substrate material with a perfect dielectric –
vacuum. In addition to improving the decay lifetimes of the qubits, our technique modifies
their magnetic noise environment. This could provide insight into the origin of the yet
unexplained excess flux noise that affects the performance of tunable qubits and other
SQUID-based devices.
P1-50 Optical properties of an atomic ensemble coupled to a band edge of a photonic
crystal waveguide
Ewan Munro, Leong Chuan Kwek and Darrick Chang
Abstract: Photonic crystal waveguides (PCWs) have attracted significant interest in recent
years as a platform for realizing novel quantum light-matter interfaces. The ability to
engineer their dispersive and modal properties via design and fabrication permits control of
the electromagnetic environment experienced by nearby atoms, which may be leveraged to
achieve strongly-enhanced atom-photon coupling efficiencies, as well as for the exploration
of new regimes of quantum optics. An exciting example of the latter is the ability to engineer
long-range coherent interactions between atoms, which occurs when the atomic transition
frequency is inside a band gap of the PCW. Here we investigate the fundamental optical
properties of an ensemble of such atoms, finding rich features that differ markedly from
standard atomic ensembles. The linear spectrum exhibits a range of resonant features,
some of which may be used for characterization of the ensemble, and which moreover
display strong optical nonlinearities that yield strong photon anti-bunching in the scattered
light. Our results are of direct relevance to atom-PCW experiments that should soon be
realizable.
55
P1-51 Practical Quantum Retrieval Games
Juan Miguel Arrazola, Markos Karasamanis and Norbert Lutkenhaus
Abstract: Complex cryptographic protocols are often constructed from simpler buildingblocks. In order to advance quantum cryptography, it is important to study practical buildingblocks that can be used to develop new protocols. An example is quantum retrieval games
(QRGs) which have broad applicability and have already been used to construct quantum
money schemes. In this work, we introduce a general construction of quantum retrieval
games based on the hidden matching problem and show how they can be implemented in
practice using available technology. More precisely, we provide a general method to
construct (1-out-of-k) QRGs, proving that their cheating probabilities decrease exponentially
in k. Additionally, we show how they can be implemented using sequences of phaseencoded coherent states and linear optics, even in the presence of experimental
imperfections. Our results are a new tool in the arsenal of the practical quantum
cryptographer.
P1-52 Non-local games and optimal steering at the boundary of the quantum set
Yi-Zheng Zhen, Koon Tong Goh, Yu-Lin Zheng, Wen-Fei Cao, Xingyao Wu, Kai Chen and
Valerio Scarani
Abstract: The boundary between classical and quantum correlations is well characterised by
linear constraints called Bell inequalities. It is much harder to characterise the boundary of
the quantum set itself in the space of no-signaling correlations. By looking at the question
from the perspective of non-local games based on steering, Oppenheim and Wehner (OW)
found an intriguing property of specific points of the quantum boundary: the local state of
Bob is steered to one that saturates a local fine-grained uncertainty relation. Our work brings
to the fore the question of whether the OW condition characterises the whole of the quantum
boundary, in any scenario.
P1-53 Multiparty Quantum Signature Schemes
Juan Miguel Arrazola, Petros Wallden and Erika Andersson
Abstract: Digital signatures are widely used in electronic communications to secure
important tasks such as financial transactions, software updates, and legal contracts. The
signature schemes that are in use today are based on public-key cryptography and derive
their security from computational assumptions. However, it is possible to construct
unconditionally secure signature protocols. In particular, using quantum communication, it is
possible to construct signature schemes with information-theoretic security based on
fundamental principles of quantum mechanics. Several quantum signature protocols have
been proposed, but none of them has been explicitly generalised to more than three
participants, and their security goals have not been formally defined. Here, we first extend
the security definitions of Swanson and Stinson so that they can apply also to the quantum
case, and introduce a formal definition of transferability based on different verification levels.
We then prove several properties that multiparty signature protocols with informationtheoretic security -- quantum or classical -- must satisfy in order to achieve their security
goals. We also express two existing quantum signature protocols with three parties in the
security framework we have introduced. Finally, we generalize a quantum signature protocol
by Dunjko et al. to the multiparty case, proving its security against forging, repudiation and
non-transferability. Notably, this protocol can be implemented using any point-to-point
quantum key distribution network and therefore is ready to be experimentally demonstrated.
56
P1-54 A scheme for estimating accidental coincidence rates between saturated single
photon detectors: the effective duty cycle
James Grieve, Rakhitha Chandrasekara, Zhongkan Tang, Cliff Cheng and Alexander Ling
Abstract: In the field of quantum photonics, the correlated detection of single photons is a
routine task, with applications in experiments as diverse as metrology and quantum key
distribution. In any such experiment, two or more single photon detectors are operated in
parallel, with their signals combined via hardware or post-processing to produce a
coincidence signal.
Since two uncorrelated streams of photons will occasionally produce coincidences by
chance, care must be taken to minimise the contribution of such “accidental” coincidences,
typically by operating the entire experiment at a very low throughput. In many cases
however, it is sufficient to simply subtract these spurious events in post-processing, for
which a good estimation of their rate is essential. Unfortunately, such estimations typically
require assumptions which are only valid at low rates, where the detector count rates
respond in an approximately linear fashion to the incoming event stream. At higher rates, socalled “saturation” behaviour of the single photon detector results in markedly non-linear
behaviour, reducing the useful range of event rates which can be detected.
In this presentation we discuss a general method for estimating rates of accidental
coincidence at rates commonly associated with these saturation effects and non-linear
behaviour. By combining the effects of the recovery time of both detector circuits and the
waiting-time statistics of the light source into an “effective duty cycle” we are able to
accommodate arbitrarily complex recovery behaviour at high event rates.
In our discussion, we provide a detailed high-level model for the recovery process of
passively quenched avalanche photodiodes, and demonstrate effective accidental
coincidence subtraction at rates commonly considered outside of the range of these
detectors. By post-processing experimental data using our model, we observe an
improvement in the visibility of polarization correlation fringes from 88.7% to 96.9% over a
large dataset with highly varying flux.
We belive this technique will be useful in improving the signal-to-noise ratio in applications
which depend on coincidence measurements, especially in situations where rapid changes
in flux may make a rate-limiting strategy impossible. Although we will present a detailed
treatment for passively quenched APDs, we emphasise the very general nature of this
estimation strategy, and will provide explicit protocols for its application to arbitrary detector
technologies and incoming event statistics.
This work recently appeared in Optics Express: http://dx.doi.org/10.1364/OE.24.003592
57
P1-56 Highly confining direct written waveguides for integrated quantum photonics
James Grieve, Bo Xue Tan and Alexander Ling
Abstract: Compact waveguide chips fabricated by femtosecond direct write in glass have
become a powerful and mature tool for the realisation of large scale quantum photonics
experiments, with a number of implementations discussed extensively in the literature. To
date, most work in this area has utilized a femtosecond oscillator with an external amplifier,
with the resulting few-kilohertz pulse train providing the high pulse energies needed to
achieve permanent modification of the substrate material. These pulses are brought to a
focus with relatively low numerical aperture optics, and the resulting waveguides exhibit a
pronounced asymmetric cross-section due to the point spread function of the lens. This may
be problematic in quantum optics experiments which make use of the polarization of photons
to encode quantum information, as shape-induced birefringence may cause degradation of
the guided photon state.
We have developed a femtosecond laser direct write waveguide platform that employs a
minimally modified commercial oscillator without amplification and a high numerical aperture
objective to fabricate waveguides in the flint glass SF11. With high repetition rates and pulse
energies only slightly above the threshold for modification, multiple pulses contribute to the
waveguide morphology which is no longer dominated by the point spread function. The
resulting waveguides exhibit markedly reduced aspect ratio when compared to those
produced by amplified systems, and also feature a small mode cross-section (around 1.6um
FWHM), which we attribute to an unusually high peak modification of the refractive index.
This increased mode confinement may enable reduced bending radius, and allow for a
further reduction in the scale of large photonic circuits.
In this contribution, we will discuss the fabrication process, as well as present data on the
performance of bus waveguides and optical components such as directional couplers. It is
our belief that this novel fabrication scheme will provide an attractive alternative to
conventional, high pulse energy systems. The reduced cost associated with our oscillatoronly approach will also help to lower the barriers to participation in this promising area of
research.
P1-57 Engineering high brightness and high efficiency in downconversion sources
Brigitta Septriani, James Grieve, Alexander Ling and Kadir Durak
Abstract: The workhorse technique for generating correlated pairs of photons is based on
spontaneous parametric downconversion in nonlinear crystals. These photon pair sources
are usually designed with relatively short crystal lengths, in the belief that this is necessary to
attain good performance. We show, contrary to common practice, that concurrent high
brightness and efficiency is also available to longer crystals. We present comprehensive
measurement data on the pump and collection beam parameters necessary to achieve high
collection efficiency (89.01.7% and 81.93.7% for signal and idler) together with high
brightness when a single thick b-Barium Borate crystal (15.76mm) is pumped with a narrow
linewidth laser.
We observe a linewidth broadening in the spectrum of the downconverted light when
compared to numerical simulation, which we associate with an effective interaction length
defined only by the overlap of the pump and collection modes within the crystal volume. This
contrasts with commonly used “thin-crystal” geometries, in which the interaction length is
defined by the length of the crystal. We note that this reduction in the effective interaction
length is the result of spatial walk-off of the pump beam. We also conduct a systematic
mapping of brightness and efficiency by varying the pump and collection mode sizes. Our
data convincingly demonstrates high brightness and efficiency over a range of focusing
conditions, highlighting the robust nature of this source design.
58
The surprising results from this work will be of interest to optical designers and those
involved in the construction and operation of photon pair sources, particularly where both
high brightness and efficiency are required. Field deployment of these devices often imposes
strict limits on size, weight and power (SWAP), and we belive the adoption of a thick-crystal
BBO strategy may open up new opportunities for correlated photon sources in real-world
scenarios.
This work has just been accepted for publication by Optica (http://arxiv.org/abs/1511.04159).
P1-58 Multiphoton entanglement from single photon sources
Jun-Yi Wu and Holger F. Hofmann
Abstract: We study the experimentally accessible properties of multi-photon entanglement
generated by single photon sources and beam splitters. As the photon number increases, it
is possible to observe a rich variety of structures in the photon distributions obtained after
linear optics transformations. In this presentation, we focus on the patterns obtained from the
unbiased interference of all modes that is described by a discrete Fourier transformation of
the light field amplitudes and show how the entanglement can be characterized using the
correlations of photon statistics observed in the two multi-mode outputs.
P1-59 Optical Resources and the Maxwell Demon
Angeline Shu, Jibo Dai and Valerio Scarani
Abstract: A recent experimental study explored the power of an optical Maxwell demon to
extract work from thermal states at the same temperature [Vidrighin et al., Phys. Rev. Lett.
\textbf{116}, 050401 (2016)]. We present a study of the effect of the demon when one uses
resource states that are easy to implement.
P1-60 Full reconstruction of a 14-qubit state within 4 hours
Zhibo Hou and Guo-Yong Xiang
Abstract: Full quantum state tomography (FQST) plays a unique role in the estimation of the
state of a quantum system without a priori knowledge or assumptions. Unfortunately, since
FQST requires informationally (over)complete measurements, both the number of
measurement bases and the computational complexity of data processing suffer an
exponential growth with the size of the quantum system. A 14-qubit entangled state has
already been experimentally prepared in ion trap, and the data processing capability for
FQST of a 14-qubit state seems to be far away from practical applications. In this paper, the
computational capability of FQST is pushed forward to reconstruct a 14-qubit state with a run
time of only 3.35 hours using the linear regression estimation (LRE) algorithm, even when
informationally overcomplete Pauli measurements are employed. The computational
complexity of LRE algorithm is first reduced from O(10^19) to O(10^15) for a 14-qubit state
by dropping all the zero elements and its computational efficiency is further sped up by fully
exploiting
the parallelism of LRE algorithm with parallel Graphic Processing Unit (GPU) programming.
Our result can play an important role in quantum information technologies with large
quantum systems.
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P1-61 Scalable quantum router architecture with code interoperability
Shota Nagayama, Shigeya Suzuki, Takahiko Satoh, Takaaki Matsuo and Rodney Van Meter
Abstract: The future Quantum Internet will require scalable quantum routers, modied
quantum repeaters that are capable of three or more long distance connections and of
routing among the connections, and that support error correcting code conversion for
interoperability. We suggest a quantum router architecture which satisfies the requirements
above and analyze the error probability of a generalized procedure for creating Bell pairs
with each qubit encoded in a different error correcting code mentioned often in quantum
repeater research. Based on our analysis, the combination of purification before encoding
and purification after encoding with post-selection may result in lower residual error rate,
therefore this combination and our router architecture may be preferred for practical
quantum routers for the world wide Quantum Internet.
P1-62 Entanglement of quantum circular states of light
Mikhail Kolobov, Dmitri Horoshko, Stephan De Bievre and Giuseppe Patera.
Abstract: We consider a class of quantum macroscopic superposition of coherent states
equidistant on a circle in phase space. Such states generalize well-known even and odd
coherent states to N-component quantum superposition. We derive analytical expression for
entanglement and discuss the measure of non-classicality for these states. Our results
demonstrate a peculiar behavior of entanglement and non-classicality due to N-component
quantum interference in phase space.
P1-66 Wide-area topology of a Quantum Internet
Takaaki Matsuo, Takahiko Satoh, Shota Nagayama, Shigeya Suzuki and Rodney Van Meter
Abstract: The purpose of this research is to generate reasonable quantum topologies for a
reliable Quantum Internet simulation. As Quantum Internet is expected to be complementary
to the classical Internet, we extracted sub-topologies from existing classical Internet, and
modified them into quantum topologies. In order to assess the accuracy of our generation
method, we used statistical comparison between generated topologies and classical raw
topologies. As a result, generated topologies showed statistically similar characteristics to
the existing real world topologies. Therefore, topologies generated by our method can be
considered reasonable for a Quantum Internet simulation.
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P1-70 Towards storage of single quantum dot photons in a rubidium quantum
memory
Janik Wolters, Lucas Beguin, Jan-Philipp Jahn, Mathieu Munsch, Andrew Horsley, Fei Ding,
Aline Faber, Andreas Jöckel, Andreas Kuhlmann, Armando Rastelli, Oliver G. Schmidt,
Richard J. Warburton and Philipp Treutlein
Abstract: The availability of quantum networks promises a plethora of radically new
applications and novel insights. However, establishing the hardware for a quantum network
is a challenging task. A source of indistinguishable single photons is required along with
means to store the single photons at each network node. For single photon generation,
semiconductor quantum dots have emerged as a prime resource, as they provide triggered
single-photon emission at a high rate and with high spectral purity. Independently, atomic
ensembles have emerged as one of the best quantum memories for single photons,
providing high efficiency storage and long memory lifetimes.
We report on our efforts to combine these two disparate physical systems to exploit the best
features from both worlds. On the one hand, we have developed a novel type of
GaAs/AlGaAs quantum dot single photon source that emits narrow-band single-photons (∆ν
∼ 1 GHz) at Rb wavelengths. On the other hand, we are pushing forward an EIT-based
quantum memory to store these photons in a dense ensemble of Rb87 atoms.
P1-71 Quantum teleportation between multiple senders and receivers
Seung-Woo Lee, Hee Su Park and Hyunseok Jeong
Abstract: Quantum teleportation is a core protocol to realize quantum communication and
quantum computation. In order to realize quantum communication in network, it may be
essential to realize an efficient way to transfer unknown quantum states among multiple
participants. A teleportation protocol from one sender to many receivers was proposed
previously and demonstrated experimentally, but any protocol to transfer quantum states
possesed by multiple senders, possibly separated spatially or temporally in communication
network, directly to the others has been missing so far. Here we propose a scheme for
teleportation between arbitrary number of senders and receivers, and report its experimental
demonstration with linear optics and multi-photon entanglement as a proof-of-principle test.
The main achievements of our work are not only to propose a protocol for quantum
teleportation between arbitrary participants with its experimental demonstration, but also to
realize the near-deterministic Bell state measurement with linear optics proposed recently in
[Phys. Rev. Lett. 114, 113603 (2015)]. We expect our work to pave the way to realization of
multiparty quantum teleportation in network.
P1-72 On-chip coherent conversion of photonic quantum entanglement between
different degrees of freedom
Lantian Feng, Ming Zhang, Zhaiyuan Zhou, Ming Li, Xiao Xiong, Le Yu, Baosen Shi,
Guoping Guo, Daoxin Dai, Xifeng Ren and Guangcan Guo
Abstract: In the quantum world, a single particle can have various degrees of freedom to
encode the quantum information. Therefore, efficiently and fully controlling of those degrees
of freedom simultaneously is on demanding. For example, path or polarization degree of
freedom of single photons has been used in the recent investigations of quantum photonic
integrated circuits (QPICs), while usually only one of them was used. Here, we introduce the
transverse waveguide mode degree of freedom to QPICs, and demonstrate the coherent
conversion of photonic quantum entangled state (NOON state) between different degrees of
freedom on a single chip for the first time. By using mode multiplexers and mode converters,
single photons in different optical paths or different polarizations can be converted to/back to
different transverse waveguide modes in a single multi-mode waveguide, with the latter
61
being an ideal platform for higher dimensional quantum information processes. The
preservation of quantum coherence in these conversion processes is proven by single
photon and two photon quantum interference using a fiber beam-splitter (BS) or on-chip
BSs. These results provide us with the ability to control and convert multiple degrees of
freedom of photons for the QPIC-based quantum information process.
P1-73 Experimental quantum fingerprinting with weak coherent states
Juan Miguel Arrazola, Feihu Xu, Keijin Wei, Wenyuan Wang, Pablo Palacios-Avila, Chen
Feng, Shihan Sajeed, Hoi-Kwong Lo and Norbert Lutkenhaus
Abstract: Quantum communication holds the promise of creating disruptive technologies that
will play an essential role in future communication networks. For example, the study of
quantum communication complexity has shown that quantum communication allows
exponential reductions in the information that must be transmitted to solve distributed
computational tasks. Recently, protocols that realize this advantage using optical
implementations have been proposed. Here we report a proof-of-concept experimental
demonstration of a quantum fingerprinting system that is capable of transmitting less
information than the best-known classical protocol. Our implementation is based on a
modified version of a commercial quantum key distribution system using off-the-shelf optical
components over telecom wavelengths, and is practical for messages as large as 100 Mbits,
even in the presence of experimental imperfections. Our results provide a first step in the
development of experimental quantum communication complexity.
P1-74 SpooQySats: nanosatellites to demonstrate technologies for future quantum
communication networks
Robert Bedington, Cliff Cheng, Yue Chuan Tan, Edward Truong-Cao, Xueliang Bai and
Alexander Ling
Abstract: SpooQySats are 10x10x30cm CubeSat nanosatellites that will be assembled and
operated from the Centre For Quantum Technologies (CQT) to test and validate our
upcoming SPEQS (Small Photon Entangling Quantum System) entangled photon sources,
in preparation for future space-to-ground QKD (Quantum Key Distribution) demonstration
missions.
CubeSat is the industry standard specification for nanosatellites and has spawned a rapidly
growing industry of compatible subsystems and services. Our SpooQySats are being based
around the latest platform produced by the Danish company GomSpace which they
demonstrated aboard GomX-3: an advanced CubeSat deployed into orbit from the
International Space Station (ISS) in October 2015. Key components include the AX100
digital UHF radio transceiver and A3200 onboard computer which are highly miniaturised so
that they can both be mounted onto a single PC104 board.
The platform allows for a significant amount of flexibility and a range of SpooQySat designs
have been researched, including SpooQy-lite (a 10x10x20cm design) and SpooQy-Max
(which contains redundant spares of key sub-systems). Our preferred launch option for
SpooQySats is deployment from the ISS as this represents a suitable compromise between
ease of access, flyover frequency, regular launches, cost, mission lifetime and proven
effectiveness with GomX-3.
Communications with SpooQySats will be made over UHF with a new ground station we are
building at NUS and with the ground stations of collaborating partners around the world.
Future missions may additionally use S-band radios to allow for increased data rates.
To ensure that the satellites will survive the rocket launch and operate effectively in the
space environment, various tests need to be performed. These include vibration and shock
62
tests (to simulate the launch) and thermal cycling tests performed under vacuum (the
combination often referred to as “shake and bake”). Particular attention must be paid to
testing the CQT payload as the GomSpace product lines are already qualified to be space
compatible. An additional concern of the space environment is ionising radiation. While
traditional space-compatible parts are thoroughly tested and optimised for such
environments, many cheaper commercial parts are not requiring us to perform our own tests
to determine suitability and expected lifetimes. Early versions of the SPEQS payload have
already been demonstrated to survive these tests.
The objective of the initial SpooQySats will be to perform Bell's inequality violations in-situ
using the SPEQS source and to investigate how its performance is affected by regular
operation in space. No photons will be beamed outside of the satellite. In later missions we
hope to collaborate with other groups specialising in transmission optics, high performance
attitude determination/control systems, and space-to-ground laser communications to take
additional steps towards space-to-ground QKD demonstration using nanosatellites.
P1-75 Many-box locality
Yu Cai, Jean-Daniel Bancal and Valerio Scarani
Abstract: It has been a long standing question to search for physical principles that defines
quantum physics. Within the framework of no-signalling theories, several principles have
been proposed to single out the quantum set of distributions. However, all previous
proposed principles are satisfied by the "almost quantum" set, a set of distributions provably
larger than the quantum set. By modifying the assumptions of one of these principles,
namely Macroscopic Locality (ML), we propose the principle of Many-Box Locality (MBL).
Here we will present the tools we developed to study the MBL_N sets as well as some
preliminary results on the characterization of MBL_N sets.
P1-76 All the self-testings of the singlet for two binary measurements
Yukun Wang, Xingyao Wu and Velario Scarani
Abstract: Self-testing refers to the possibility of characterizing uniquely (up to local
isometries) the state and measurements contained in quantum devices, based only on the
observed input-output statistics. Already in the basic case of the two-qubit singlet, selftesting is not unique: the two known criteria (the maximal violation of the CHSH inequality
and the Mayers–Yao correlations) are not equivalent. It is unknown how many criteria there
are. In this paper, we find the whole set of criteria for the ideal self-testing of a singlet with
two measurements and two outcomes on each side; it coincides with all the
extremal points of the quantum set that can be obtained by measuring the singlet.
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P1-77 BosonSampling with continuous variable measurements
Austin Lund, Saleh Rahimi-Keshari and Timothy Ralph
Abstract: We show that the classical hardness argument of Aaronson and Arkipov can be
extended to a scheme involving only continuous variable measurements on the output of a
BosonSampling device. Our argument is presented for exact BosonSampling using matrices
whose permanent is not near zero. We discuss the impediments to extending this result to
approximate sampling.
P1-78 Implementation of high-performance coincidence counting unit with a low-cost
field programmable gate array
Byung Kwon Park, Yong-Su Kim, Osung Kwon, Sang-Wook Han and Sung Moon
Abstract: We present a CCU with high speed and a short coincidence time window using a
low-cost FPGA (Altera DE0-Nano Development and Education Board with a Cyclone IV
FPGA chip, less than $100). The CCU was programmed with Verilog hardware description
language (Verilog HDL). It has 8 logic inputs, and the internal delays of each input can be
tuned independently with the resolution of 0.7 ns using buffers embedded in the FPGA. The
maximum input frequency and the minimum coincidence time window are 163 MHz and 0.47
ns, respectively. It has 12 outputs including 8 single-input counts and 4 coincidence counts,
however the number of inputs and outputs can be easily increased if necessary. The
coincidence configurations up to 8 inputs, i.e., eight-fold coincidences, can be chosen by the
user. The CCU is connected with a USB-to-serial board (ROVITECK, I-FT232H) to
communicate with a personal computer via a universal serial bus (USB). All the parameters,
including the size of the coincidence time window, the internal delays of the input channels,
and the coincidence configurations, are easily defined and adjusted with the graphic user
interface (GUI) programmed with LabView or C]. We remark that the total component price
of this high performance CCU costs under $200. With its excellent performance at a low-cost
implementation, our CCU is ready to be employed in quantum optics and quantum
information laboratories.
P1-79 Quantum Noise Spectroscopy
Gerardo Paz Silva, Leigh Norris and Lorenza Viola
Abstract: We present spectroscopy protocols capable of characterizing an environment
coupling to multiple qubits. Concretely, we are able to reconstruct the correlation functions of
the bath in frequency space, i.e., the power spectra of the environment. This is achieved by
measuring the response of the qubits under control pulses with particular symmetries and in
the presence of the bath of interest. We discuss implications of these protocols to quantum
control, metrology, and fault-tolerant quantum computing.
64
P1-80 Continuous-mode analysis of a noiseless linear amplifier
Yi Li, Andre Carvalho and Matthew James
Abstract: We develop a dynamical model to describe the operation of the non-deterministic
noiseless linear amplifier (NLA) proposed by Ralph and Lund in the regime of continuous
modes inputs. We analyse the dynamics conditioned on the detection of photons and show
that the amplification gain depends on detection times and on the temporal profile of the
input state and the auxiliary single photon state required by the NLA. We also show that the
output amplified state inherits the pulse shape of the ancilla photon.
P1-81 Device-independent parallel self-testing of two singlets
Xingyao Wu, Jean-Daniel Bancal, Matthew Mckague and Valerio Scarani
Abstract: Device-independent self-testing is the possibility of certifying the quantum state
and the measurements, up to local isometries, using only the statistics observed by querying
uncharacterized local devices. In this paper, we study parallel self-testing of two maximally
entangled pairs of qubits: in particular, the local tensor product structure is not assumed but
derived. We prove two criteria that achieve the desired result: a double use of the ClauserHorne-Shimony-Holt inequality and the $3\times 3$ Magic Square game. This demonstrate
that the magic square game can only be perfectly won by measureing a two-singlets state.
The tolerance to noise is well within reach of state-of-the-art experiments.
P1-83 Demonstration of Quantum Permutation Algorithm with a Single Photon
Ququart
Pei Zhang
Abstract: We report an experiment to demonstrate a quantum permutation determining
algorithm by employing photon polarization and spatial modes. The quantum permutation
determining algorithm displays the speedup of quantum algorithm by determining the parity
of the permutation in only one step of evaluation compared with two for classical algorithm.
This experiment is accomplished in single photon level and the method exhibits universality
in high-dimensional quantum computation.
P1-84 Experimental evaluation of quantum correlations between measurement errors
using polarization-entangled photons as probe input
Yutaro Suzuki, Masataka Iinuma, Masayuki Nakano and Holger F. Hofmann
Abstract: We investigate the correlations between measurement errors when two noncommuting polarization components are jointly measured using a polarization filter set to an
intermediate angle between the two target polarizations. Using entangled photon pairs as
input, we can distinguish the rates of individual errors from the rates at which errors happen
jointly by comparing the known correlations of the input with the experimentally observed
correlations between the measurement outcomes. The results show that the correlations
between the errors are consistent with the non-classical correlations between the operator
observables expressed by the commutation relations.
65
P1-85 Development of a readout backend for a Geiger-mode SiPM
In-Ho Bae, Dong-Hoon Lee and Seongchong Park
Abstract: Photon counting detectors such as avalanche photodiodes (APDs) and
photomultiplier tubes (PMTs) are widely used in a variety of applications such as quantum
optics experiment, remote sensing, nuclear physics, astrophysics, and fluorescence
spectroscopy [1]. Silicon photomultiplier (SiPM), another Geiger Mode photodetector, is
based on Si technology having a similar operation principle with PMT [2]. Since it has many
promising advantages such as low magnetic susceptibility, structural robustness, compact
size, and low device cost compared to PMT of similar performance, SiPM comes into focus
for medical application [3].
In this work, we developed a readout backend for a SiPM operating in a Geiger-mode. There
are a couple of differences between conventional APDs and SiPMs in operation although
they have the same principle of light sensing mechanism. For example, Fig. 1(a) and (b)
show output current pulses from an APD (Hamamatsu C0902) and a SiPM (SensL 3020) at
breakdown voltage, respectively. Note that the figures were obtained in the persistent mode
of an oscilloscope. When the APD operated at the breakdown voltage, there were a lot of
avalanche pulses in random timing sequence. After appearance of the central avalanche
pulse, retriggering of avalanche pulses occurs randomly with subsequently arriving photons.
The amplitudes of retriggered avalanche pulses are lower than the central pulse because the
diode voltage is gradually recovered to the initial bias voltage during recovery time. On the
contrary with the APD, the SiPM does not show any recovery time as shown in Fig 1(b). It is
because output pulses from individual pixels are superimposed as the SiPM is composed of
thousands of APD pixels. Due to such differences of the SiPM, its readout backend has to
be approached differently with that of the APD. We have developed a readout backend for a
Geiger-mode SiPM and will apply it to evaluate dark count characteristics of a SiPM in order
to demonstrate its feasibility.
P1-86 The classical-quantum divergence of complexity in the Ising spin chain
Whei Yeap Suen, Jayne Thompson, Andrew Garner, Vlatko Vedral and Mile Gu
Abstract: Can quantum information fundamentally change the way we perceive what is
complex? Here, we study statistical complexity, a popular quantifier of complexity that
captures the minimal memory required to classically model a process. We construct a
quantum variant of this measure, and evaluate it analytically for a classical Ising spin chain.
The resulting complexity measure - quantum statistical complexity - exhibits drastically
different qualitative behaviour. Whereas the classical statistical complexity of the spin chain
grows monotonically with temperature, its quantum complexity rises to a maximum at some
finite temperature then tends back towards zero for higher temperatures. This demonstrates
that our notion of what is complex depends fundamentally on which information theory we
employ.
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P1-87 Experimental evaluation of non-classical correlations by sequential quantum
measurements
Masataka Iinuma, Yutaro Suzuki, Taiki Nii, Ryuji Kinoshita and Holger F. Hofmann
Abstract: Ozawa's argument on the measurement uncertainty relation implies the possibility
of exploring the relations between the measurement outcomes and the target observable.
Here, we experimentally investigate this relation and its role to the measurement errors by
performing a sequence of two non-commuting observables on the polarization components
of a single photon. The initial measurement commutes with the target observable and the
second one is only sensitive to a complimentary observable. By controlling the strength of
the initial measurement, we can change the balance between the classical and the nonclassical correlations in the quantum measurement.
The experimental results show that quantum correlation between the initial and
the final measurement outcomes significantly reduces the measurement error, even though
the polarization component detected in the final measurement is orthogonal to the target
polarization.
P1-88 Interferences in quantum eraser reveal geometric phases in modular and weak
values
Mirko Cormann, Mathilde Remy, Branko Kolaric and Yves Caudano
Abstract: In this letter, we present a new procedure to determine completely the complex
modular values of arbitrary observables of pre- and post-selected ensembles, which works
experimentally for all measurement strengths and all post-selected states. This procedure
allows us to discuss the physics of modular and weak values in interferometric experiments
involving a qubit meter. We determine both the modulus and the argument of the modular
value for any measurement strength in a single step, by controlling simultaneously the
visibility and the phase in a quantum eraser interference experiment. Modular and weak
values are closely related. Using entangled qubits for the probed and meter systems, we
show that the phase of the modular and weak values has a topological origin. This phase is
completely defined by the intrinsic physical properties of the probed system and its time
evolution. The physical significance of this phase can thus be used to evaluate the
quantumness of weak values.
P1-89 Coherent-state discrimination via non-heralded probabilistic amplification
Matteo Rosati, Andrea Mari and Vittorio Giovannetti
Abstract: A scheme for the detection of low-intensity optical coherent signals is presented
based on non-linear operations which rely on the probabilistic amplifier by Ralph and Lund
and/or on a partial dephasing transformation of the received signals, preserving the zero and
one photon-number subspace while destroying any further coherence. The success
probability gains up to 1.85% with respect to the optimized Kennedy receiver and, when
employed in an adaptive strategy, approaches the Helstrom bound appreciably faster than
the Dolinar receiver. An optical cavity implementation of the partial dephaser is proposed
and its performances are analyzed.
67
P1-90 Entangled photon-pairs emitted from Ag/GaN photonic crystals as sources for
quantum-information processing
Dalibor Javůrek and Jan Peřina Jr.
Abstract: Metallo-dielectric photonic crystals are highly efficient sources of photon pairs. The
photon pairs are emitted in the process of spontaneous parametric down-conversion. A
perturbative quantum-mechanical model of SPDC in layered media has been developed.
The one-dimensional metallo-dielectric photonic crystal consisting of eleven GaN/Ag layers
has been designed in order to achieve the highest photon-pair emission rate. In the
designed crystal, the quantities characterizing a photon pair such as signal photon number
density, correlated areas or number of emitted noise photon pairs have been investigated.
The emission of photon pairs has showed up to be high due to strong resonance of downconverted TM polarized photons inside the structure. The resonance caused the emission of
the photon pairs to be highly localized both in radial emission angle and in wavelength.
P1-91 Conditioned quantum dynamics in a 1D lattice system
Ralf Blattmann and Mølmer Klaus
Abstract: We consider a quantum particle on a one dimensional lattice subject to weak local
measurements and study its stochastic dynamics conditioned on the measurement
outcomes. Depending on the measurement strength our analysis of the quantum trajectories
reveals dynamical regimes reaching from quasi-coherent wave packet oscillations to a Zenotype dynamics. We analyse how these
dynamical regimes are directly reflected in the spectral properties of the noisy measurement
records.
P1-95 Testing the limits of human vision with single photons
Rebecca Holmes, Michelle Victora, Ranxiao Frances Wang and Paul Kwiat
Abstract: The rod photoreceptor cells in the retina respond to single photons, but it is not yet
known whether this leads to perception of the light. We discuss techniques using a heralded
single-photon source to study the lower limit of human vision, and report some recent
improvements, including the use of EEG-contingent stimulus presentation.
P1-97 Entanglement Restoration in Amended Entanglement Breaking Channels
Álvaro Andrés Cuevas Seguel, Andrea Mari, Antonella De Pasquale, Adeline Orieux,
Marcello Massaro, Fabio Sciarrino, Vittorio Giovanetti and Paolo Mataloni
Abstract: Let’s consider two entangled photons, with one of them representing our testing
system S and the other photon playing the role of an ancilla A. Then, apply a quantum
channel acting on S, such that, when applied twice, the result is an entanglement loss.
These channels are said to be Entanglement Breaking Channels of order 2 (EBC-2). Here
we show the behavior of such entanglement breaking channels, realized by a proper
sequence of local Amplitude Damping Maps, in which a system S belonging to a
polarization-entangled photon state is injected. In these conditions, we demonstrate how to
restore the entanglement in presence of these channels. This is demonstrated by a
sequence of two similar channel pairs, giving a four-channel transmission line M+M+N+N, a
structure that destroys the entanglement more efficiently than only two EBC-2. In this case,
we prove both theoretically and experimentally that it is possible to reconstruct the line by
reordering its four parts as M+N+M+N. Then, by a counterintuitive mechanism this sequence
allows to restore the entanglement, giving a new channel that is no more entanglement
68
breaking. We conclude that, by using suitable techniques as the one used in our experiment,
it is possible to amend entanglement losses in different kinds of noisy channels.
P1-98 Proper Dimension Witnessing
Wan Cong, Yu Cai, Jean-Daniel Bancal and Valerio Scarani
Abstract: Dimension witnessing, first introduced by Brunner et al in [1], is a device
independent technique to obtain a lower bound on the quantum dimension of a system.
Dimension witnesses can be obtained as linear inequalities on the observed statistics
$sum_{cz}s_{cz}P(c|z)\leq S_d$: a violation of the inequality guarantees that the measured
systems are of a dimension higher than d. Dimension can be witnessed for single systems
[2] or for composite ones. In the latter case, if the dimension witness is based on a Bell
inequality [1, 3], it also rules out a classical origin for the correlations. Specifically, Ref [1]
proved that a sufficiently high violation of the CGLMP3 inequality [4] excludes the possibility
that a pair of qubits is being measured. We have proved that CGLMP4 has a similar
property: it has a bound for qubits and a bound for qutrits; a violation above the latter
certifies that two ququarts or larger systems are being measured. However, we have also
noticed that the qutrit bound for CGLMP4 can be violated with sequential measurements on
two pairs of qubits. This observation begs the question of what one is actually testing. On the
one hand, two pairs of qubits do form a system of two ququarts: as such, the dimension
witnessing is not flawed. On the other hand, just by grouping together two emissions of a
two-qubit source, one would not claim to have the freedom to perform all ququart
measurements, which seems to be the real motivation of using a dimension witness. We
have proved that sequential measurements on two-qubit sources can also lead to a violation
of the qubit bound of CGLMP3 and to an almost maximal violation of CGLMP8. It may
ultimately be the case that the CGLMP family does not give dimension witnesses with all the
desired properties, and one will have to find others. Therefore, we propose a deviceindependent certification of a Bell-state measurement (BSM) as a proper dimension witness.
This certification is a modification of the method used in [5]. We show that in satisfying this
criteria, the measurements needed cannot be done sequentially on two qubits, hence
demonstrating the ability to perform a non-trivial ququart measurement.
References
[1] N. Brunner, S. Pironio, A. Acin, N. Gisin, A. A. Methot, and V. Scarani. “Testing the
Dimension of Hilbert Spaces”. Phys. Rev. Lett. 100.21 (2008), p. 210503.
[2] N. Brunner, M. Navascués, and T. Vértesi. “Dimension Witnesses and Quantum State
Discrimination”. Phys. Rev. Lett. 110.15 (2013), p. 150501.
[3] K.F. Pal, T.Vertesi. “Bounding the Dimension of Bipartite Quantum Systems”. Phys. Rev.
A 79 (2009), 042106.
[4] D. Collins, N. Gisin, N. Linden, S. Massar, and S. Popescu. “Bell Inequalities for
Arbitrarily High-Dimensional Systems”. Phys, Rev. Lett. 88.4 (2002), p. 040404.
[5] R. Rabelo, M. Ho, D. Cavalcanti, N. Brunner, and V. Scarani. “Device-Independent
Certification of Entangled Measurements”. Phys. Rev. Lett. 107.5 (2011), p. 050502.
69
P1-99 Past of a photon inside an interferometer
Yink Loong Len, Jibo Dai, Berge Englert and Leonid Krivitsky
Abstract: In 2013, A. Danan et. al. [1] reported an experiment that aims to answer "where
were the photons passing through an interferometer?". They concluded that "the photons do
not always follow continuous trajectories", and "only the description with both forward and
backward evolving quantum states provides a simple and intuitive picture of pre- and postselected quantum particles". The experiment, however, used classical light and statistics,
and no conclusion about single photons can be made. In this work, we set up a similar but
simplified experiment. Using entangled down-conversion photons, we were able to study the
past of single photons, where the path information of the (signal) photons that entered the
interferometer are encoded in the polarizations of their down-conversion partner (idler)
photons. The path information is extracted by performing measurement of unambiguous
discrimination (MUD) on the idler photons. Our results show that the standard formalism of
quantum mechanics, and concepts of path knowledge and interference visibility, do
sufficiently provide simple and straightforward explanation of the observed results. There is
no ambiguity that leads us to conclude discontinuous trajectories. We stress that one could
only speak of trajectory only when path knowledge is available, and it will always be
continuous. When no path information is available, corresponding to inconclusive result in
MUD, the concept of trajectory is simply undefined.
[1] A. Danan, D. Farfurnik, S. Bar-Ad, and L. Vaidman, Phys. Rev. Lett., 111, 240402 (2013).
P1-100 Quantum error correction in the presence of small baths
Yink Loong Len, Yicong Zheng and Hui Khoon Ng
Abstract: For the implementation of a realistic quantum computer, an important element is
quantum error correction (QEC), in which one actively detects and corrects errors that
occurs in the physical system. In the standard QEC analysis, the error or noise model
usually falls under two categories.
1. Memoryless noise, in which one describes the noise by using completely positive,
trace-preserving (CPTP) maps (or Lindblad master equation for continuous time) that
acts on the system only. Since any effect from its coupling with the environment or
bath is disregarded, the bath carries no information or memory about the system at
all.
2. Memory-full noise or Hamiltonian noise, in which one studies the joint unitary
evolution of the full system and bath. With the full bath included, one has a closedsystem unitary dynamics, such that any initial information encoded in the system is
always preserved within the system+bath.
Depending on which error models, one can get very different results for the fault-tolerance
threshold, i.e. a theoretical bound below which efficient quantum computer is not possible.
However, in reality, we expect the experimental situation to fall somewhere in between the
two extremes, with a small number of degrees of freedom providing some memory capacity
for information to how to and from the system, but also couple to a dissipative bath that limits
the memory. These few strongly-coupled degrees of freedom are identified as small baths.
In this poster, we show some initial steps towards a more realistic analysis of the effective
error on the system with QEC, taking into account the presence of small baths. In particular,
we derived the necessary and sufficient condition for perfect QEC with the baths included.
Using a spin model and 5-qubit code, we also studied how is the performance of QEC
affected due to the presence of small baths. From our simulations, we find that there is an
optimal rate for high quality QEC, and frequent applications of QEC is not necessarily the
better.
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P1-104 Efficient Quantum Compression for Identically Prepared Mixed States
Yuxiang Yang, Giulio Chiribella and Daniel Ebler
Abstract: We present one-shot compression protocols that optimally encode ensembles of N
identically prepared mixed states into O(log N) qubits. In contrast to the case of pure-state
ensembles, we find that the number of encoding qubits drops down discontinuously as soon
as a nonzero error is tolerated and the spectrum of the states is known with sufficient
precision. For qubit ensembles, this feature leads to a 25% saving of memory space. Our
compression protocols can be implemented efficiently on a quantum computer.
P1-106 When is simpler thermodynamically better?
Andrew Garner, Jayne Thompson, Vlatko Vedral and Mile Gu
Abstract: Living organisms capitalize on their ability to predict their environment to maximize
their available free energy,and invest this energy in turn to create new complex structures. Is
there a preferred method by which this manipulation of structure should be done? Our
intuition is "simpler is better," but this is only a guiding principal. Here we substantiate this
claim by thermodynamic reasoning. We present a framework for the manipulation of patterns
- ordered sequences of data - by predictive devices. We identify the dissipative costs and
how they can be minimized by the choice of memory in the predictive devices. For pattern
generation, we see that simpler is indeed better. However, contrary to intuition, when it
comes to extracting work from a pattern, any device capable of making statistically accurate
predictions can recover the entire free energy.
P1-107 Weak Value Measurements with Pulse Recycling
Courtney Krafczyk, Trent Graham, Andrew Jordan and Paul Kwiat
Abstract: Recycling undetected photons in a weak measurement can substantially improve
the signal-to-noise ratio for a given number of input photons. We demonstrate a preliminary
improvement by a factor of 1.36 over a system with no recycling, potentially reaching a factor
of 3.2 over that of a conventional measurement.
P1-108 Extreme Violation of Local Realism in Quantum Hypergraph States
Mariami Gachechialdze, Costantino Budroni and Otfried Guehne
Abstract: We study nonlocal properties of hypergraph states, or nonlocal stabilizer states,
which are generalisations of well-known graph states. We find that some families of
hypergraph states violate local realism exponentially like GHZ states but are more robust
than their graph-state analogues. In the end, we give applications in quantum metrology and
measurement-based quantum computation.
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P1-110 random numbers from vacuum fluctuations
Yicheng Shi, Brenda Chng and Christian Kurtsiefer
Abstract: We implement a quantum random number generator based on a balanced
homodyne measurement of vacuum fluctuations of the electromagnetic field. The digitized
signal is directly processed with a fast randomness extraction scheme based on a linear
feedback shift register. The random bit stream is continuously read in a computer at a rate of
about 480 Mbit/s and passes an extended test suite for random numbers.
P1-111 Rectification of light in the quantum regime
Jibo Dai, Alexandre Roulet, Huy Nguyen Le and Valerio Scarani
Abstract: One of the missing elements for realising an integrated optical circuit is a rectifying
device playing the role of an optical diode. A proposal based on a pair of two-level atoms
strongly coupled to a one-dimensional waveguide showed a promising behavior based on a
semi-classical study [Fratini et al., Phys. Rev. Lett. 113, 243601 (2014)]. Our study in the full
quantum regime shows that, in such a device, rectification is a purely multi-photon effect. For
an input field in a coherent state, rectification reaches up to 70% for the range of power in
which one of the two atoms is excited, but not both.
P1-112 Generation and measurement of four-dimensional entanglement in multi-core
optical fibers
Hee Jung Lee, Sang-Kyung Choi and Hee Su Park
Abstract: Photons with high-dimensional entanglement are of interest due to a greater
information capacity and a better error resilience compared to conventional two-dimensional
qubits. Most of high-dimensional experiments so far have been carried out using spatial
modes of photons such as orbital angular momentum (OAM) in free space. This work
focuses on generation and measurement of spatially entangled state in multi-core fibers
(MCFs) that contain four almost identical cores. Such an MCF has recently been a topic of
intensive research for application to space-division multiplexing optical communication that
overcomes the capacity limit of a single-mode fiber (SMF). We realize the high-dimensional
spatially entangled state between different MCFs by combining spontaneous parametric
down conversion (SPDC) as a photon source and a technique to measure arbitrary
supepositions of the core modes using a spatial light modulator (SLM).
P1-114 Qutrit trace invariants using Bloch matrices
Vinod Mishra
Abstract: Recently, a new approach to the representation of a qutrit [1] was presented using
spin-1 matrices. The starting point of this approach is the spin-1 sector of the 2-qubit states
represented as the Hilbert space spanned by 2 sets of Pauli matrices. Finally these 4 by 4
spin-1 matrices were replaced by 3 by 3 spin-1 matrices as they obey the same
commutation rules. At the same time another approach using 4-dimensional Bloch matrices
[2] have been used to represent 2-qubit states but with different parametrization of matrix
elements. The author has also derived the trace invariants implied by the positivity
constraints of the 2-qubit reduced density matrix. In the current work, qutrit trace invariants
have been derived and their implications for the geometrical representation as in [1] has also
been worked out.
[1] Pawel Kurzynski et al. “Three-dimensional visualization of a qutrit”, arXiv:1601.07361v1
[2] Omar Gamel, “Entangled Bloch Spheres: Bloch Matrix and two qubit state space”,
arXiv:1602.01548v1
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P1-117 Entanglement verification with detection-efficiency mismatch
Yanbao Zhang and Norbert Lutkenhaus
Abstract: Entanglement is a necessary condition for secure quantum key distribution (QKD).
When there is an efficiency mismatch between various detectors used in a QKD system, it is
still an open problem how to verify entanglement. Here we present a method to address this
problem, given that the detection-efficiency mismatch is characterized and known. The
method does not assume an upper bound on the number of photons arriving at each
threshold detector, and it works even if the efficiency mismatch can be controlled by an
adversary. Our results suggest that, the larger the efficiency mismatch is, the smaller the set
of entangled states that can be verified becomes. When there is no mismatch, our method
can verify entanglement even if the method based on squashing models [N. J. Beaudry, T.
Moroder, and N. Lutkenhaus, Phys. Rev. Lett. 101, 093601 (2008)] fails.
P1-118 Experimental Adaptive Quantum Tomography of Two-Qubit States
Stanislav Straupe, Gleb Struchalin, Konstantin Kravtsov, Igor Radchenko, Ivan Pogorelov
and Sergei Kulik
Abstract: We report an experimental realization of an adaptive quantum state tomography for
two-qubit states. A Bayesian inference is utilized to estimate the state and its properties of
interest (eg. purity, concurrence) and to infer the accuracy of estimation. We compare our
adaptive approach with random measurements which are known to be optimal in a nonadaptive case. We observe a qualitative enhancement in the estimation accuracy. The
scaling of the Bures distance to the true state (which is used as a figure of merit) with overall
number of registered events N is close to N^{-1} for pure states, while the non-adaptive
measurements gives close to N^{-1/2} scaling. Experiments are performed with polarization
states of photons produced in a spontaneous parametric down-conversion process. The
setup was designed to allow the preparation of states with variable degree of entanglement
and purity. Only factorized measurements were realized in the experiment. The performance
of entangling measurements was studied by numerical simulations. Experimental and
numerical results clearly demonstrate an advantage of the adaptive strategy over the
random measurements. Importantly, adaptive tomography, even restricted to factorized
measurements, still outperforms non-adaptive one with no restrictions on measurements.
Another important point is that adaptive tomography is less sensitive to instrumental errors.
We have studied the tomography performance in the case of artificially introduced
instrumental errors and have observed that the 'noise floor' for the adaptive protocol is lower.
This work extends adaptive state tomography to the case of multi-qubit states. We have
demonstrated the experimental feasibility of a fully adaptive Bayesian state estimation
protocol for two-qubit states, and the proposed algorithm is versatile and can be applied to
systems of arbitrary dimensions. The results discussed here were recently published in G.
Struchalin, et al. Phys. Rev. A 93, 012103 (2016).
P1-122 Single-cycle squeezing of light
Dmitri Horoshko and Mikhail Kolobov
Abstract: We describe a method for generating ultrabroadband squeezed light by parametric
downconversion in an aperiodically poled nonlinear crystal. We obtain the exact solution in
special functions for the wave equation in such a crystal with undepleted pump and linear
chirp of the spatial frequency of poling. We obtain also an approximate solution of the same
equation in elementary functions and show its good agreement with the exact solution within
the squeezing band.
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P1-124 Realization of a two-photon quantum gate based on cavity QED
Bastian Hacker, Stephan Welte, Stephan Ritter and Gerhard Rempe
Abstract: All-optical quantum technologies require a strong interaction between photons.
Despite considerable efforts across several areas of research, a deterministic interaction
between photonic quantum bits has so far not been reached, because the required
nonlinearities are hard to achieve. We have now employed one rubidium atom strongly
coupled to the light field of an optical cavity to realize the long-standing goal of a photonphoton quantum logic gate based on the deterministic Duan-Kimble protocol [1]. Two
distinct, flying photonic qubits enter our setup and emerge in a well-defined processed state.
The gate was characterized via quantum tomography and shows faithful operation with an
average fidelity well above the quantum threshold. Such a universal two-photon gate
enables a plethora of applications in quantum communication and quantum computing and
may therefore open a new era in the field of optical quantum information processing.
[1] L.-M. Duan, H. J. Kimble, Phys. Rev. Lett. 92, 127902 (2004)
P1-126 Spectrum analysis with quantum dynamical systems
Shilin Ng, Shan Zheng Ang, Mankei Tsang, Wheatley Trevor, Hidehiro Yonezawa, Akira
Furusawa and Elanor Huntington
Abstract: In this work, we proposed a theoretical framework of spectrum-parameter
estimation with quantum dynamical systems, found simple analytical results for the quantum
limits of estimating the parameters of stochastic processes, and studied measurement and
data analysis techniques that approach our limits. As an illustration to our theory, we
analyzed an experiment of continuous optical phase estimation to demonstrate the proximity
of experimental performance and our limits.
P1-127 Heisenberg’s error-disturbance relations:
experimental test
Yuan-Yuan Zhao, Paweł Kurzyński and Guo-Yong Xiang
a
joint
measurement-based
Abstract: The Heisenberg’s error-disturbance relation is a cornerstone of quantum physics. It
was recently shown to be not universally valid and two different approaches to reformulate it
were proposed. The first one focuses on how error and disturbance of two observables, A
and B, depend on a particular quantum state. The second one asks how a joint
measurement of A and B affects their eigenstates. Previous experiments focused on the first
approach. Here, we focus on the second one. Firstly, we propose and implement an
extendible method for quantum walk-based joint measurements of noisy Pauli operators to
test the error-disturbance relation for qubits introduced in Phys. Rev. A 89, 012129 (2014).
Then, we formulate and experimentally test a new universally valid relation for the three
mutually unbiased observables. We therefore establish a fundamentally new method of
testing error-disturbance relations.
P1-128 Superradiant Emission of Ultra-Bright Photon Pairs in Doppler-Broadened
Atomic Ensemble
Yoon-Seok Lee, Sang Min Lee, Heonoh Kim and Han Seb Moon
Abstract: Photon pair source with high generation rate and narrow bandwidth is one of the
most desirable quantum devices for many researchers to realize long-distance quantum
communication, where quantum entanglement swapping between completely autonomous
sources and the capability of interaction with quantum memory are essentially required.
Spontaneous parametric down-conversion (SPDC) has been widely used and constantly
74
developed as a major resource for quantum optics due to high generation rate and
scalability, such as waveguide nonlinear crystal. However, short coherence time of paired
photon limits coupling with another quantum device and causes synchronizing problem for
entanglement swapping. In the last decade, a variety of sophisticated methods have been
suggested and experimentally demonstrated for generation of the narrowband photon pairs.
One of the ingenious approaches is spontaneous four-wave mixing (SFWM), which is based
on collective excitation of atomic ensemble and successfully exploited to generation of
narrowband photon pairs using highly dense ultracold atoms. However, the need for
ultracold temperatures still limits their applicability and thus recent efforts have been made
toward replacing ultracold atoms with thermal vapor. Furthermore, the pair generation rate is
too low to be used for practical application.
Here, we experimentally demonstrate the robust and ultra-bright photon pair source with a
coincidence counting rate per input pump power of 64,600 cps/mW and relatively narrow
bandwidth using thermal vapor cell. The remarkable generation rate is achieved by
superradiant emission of photon pairs, which is attributed to coherent contribution of almost
velocity groups in Doppler-broadened ladder-type atomic ensemble. The strong timecorrelation of the paired photons exhibited the violation of the Cauchy-Schwartz inequality by
a factor of 2370 ± 150. The quadratic proportionality of the probability of detecting a heralded
single photon as a function of the optical depth clarifies that the ultra-brightness results from
the superradiance in the Doppler-broadened atomic ensemble. In addition, superradiant
beating of a single photon at a high optical depth is observed for the first time, to the best of
our knowledge; this implies coherent superposition of two-photon amplitudes from different
velocity classes. This scalable and highly bright paired photon source is ideal for quantum
entanglement swapping between completely autonomous sources and practically applicable
for room temperature quantum device in micrometer-scale vapor cell.
P1-129 Geometric spin echo under zero field
Yuhei Sekiguchi, Yusuke Komura, Shota Mishima, Touta Tanaka, Naeko Niikura and Hideo
Kosaka
Abstract: Spin echo is a fundamental tool for quantum registers and biomedical imaging. It is
believed that a strong magnetic field is needed for the spin echo to provide long memory and
high resolution since a degenerate spin cannot be controlled or addressed under a zero
magnetic field. While a degenerate spin is never subject to dynamic control, it is still subject
to geometric control. We here show the spin echo of a degenerate spin subsystem, which is
geometrically controlled via a mediating state split by the crystal field, in a nitrogen vacancy
center in diamond. The demonstration revealed that the degenerate spin is protected by
inherent symmetry breaking called zero-field splitting. The geometric spin echo under zero
field provides an ideal way to maintain the coherence without any dynamics, thus opening
the way to pseudo-static quantum RAM and non-invasive biosensors.
P1-130 Heralded quantum steering with no detection loophole over a high-loss
quantum channel
Geoff Pryde, Morgan Weston, Sergei Slussarenko, Sabine Wollmann and Helen
Chrzanowski
Abstract: Entanglement shared between remote parties is important both for fundamental
explorations of quantum physics and for a range of tasks in secure quantum
communications, remote information processing, metrology and more. Optics provides an
obvious and powerful method for sharing entangled states over long distances, but loss
through optical fibres, atmospheric transmission or diffraction effects makes it difficult or
impossible to close a Bell inequality detection loophole for far-away parties, limiting the
ability to verify that entanglement really has been shared.
75
Quantum steering (also called EPR steering) tests provide a more loss-tolerant method of
verifying entanglement. However, for losses corresponding to long-range transmission over
tens or hundreds of kilometres, the detection loophole is opened for these tests as well. Here
we consider the case where channel loss is so high that even a loss-tolerant quantum
steering protocol cannot be completed directly. We design and experimentally demonstrate a
protocol that allows quantum steering to be completed even in this case. We use
entanglement swapping to herald the presence of half of an entangled pair, after a lossy
channel, and then complete the steering protocol with the detection loophole closed.
The key experimental tools that enabled this advance were two high-performance (high
heralding efficiency and purity) entangled-photon sources which we developed, coupled with
superconducting nanowire single photon detectors (NIST).
P1-131 Entanglement degradation by macrorealistic modifications
Stefan Nimmrichter
Abstract: The steady experimental progress towards observing quantum phenomena in
nanoscopic systems has brought new attention to a controversial but intriguing idea: The
concept of macroscopic realism, i.e. the objective modification of quantum mechanics to
eliminate superpositions in the macro-world and to resolve the 'measurement problem'. Not
only will experiments soon enter a stage where the most prominent macrorealistic proposals
become testable, but the idea can also be exploited to systematically assess the degree of
macroscopicity achieved in arbitrary mechanical quantum experiments. One experiment can
be rated more macroscopic than another when it rules out a larger class of macrorealistic
modifications.
So far, the assessment of experiments with large mechanical systems has focused on
single-particle interference and coherent oscillations of nanomechanical oscillators. Here, we
study how mechanical entanglement is affected by macrorealistic modifications and what
potential degree of macroscopicity can be achieved by establishing quantum correlations
between mechanical systems.
P1-132 Scalable three-way quantum information tapping using parametric amplifiers
with quantum correlation
Nannan Liu, Xiaoying Li, Jiamin Li and Z. Y. Ou
Abstract: We demonstrate that a phase-insensitive parametric amplifier, coupled to a
quantum correlated source, can be used as a quantum information tap for noiseless threeway signal splitting. We find that the output signals are amplified noiselessly in two of the
three output ports while the other can more or less keep its original input size without adding
noise. This scheme is able to cascade and scales up for efficient information distribution in
an optical network. Furthermore, we find this scheme satisfies the criteria for a non-ideal
quantum non-demolition (QND) measurement and thus can serve as a QND measurement
device. With two readouts correlated to the input, we find this scheme also satisfies the
criterion for sequential QND measurement.
76
P1-133 Experimental demonstration of frequency-domain Hong-Ou-Mandel
interference
Toshiki Kobayashi, Rikizo Ikuta, Shuto Yasui, Shigehito Miki, Taro Yamashita, Hirotaka
Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto
Abstract: We observed the Hong-Ou-Mandel(HOM) interference between two photons with
different frequencies. In the experiment, we input a 780 nm photon and a 1522 nm photon to
a frequency converter that partially exchanges the wavelengths of the photons between 780
nm and 1522 nm. We measured coincidence counts between the output photons at 780 nm
and those at 1522 nm from the frequency converter. The observed visibility of the HOM
interference was 0.71±0.04, which clearly exceeds the maximum value of 0.5 in the classical
wave theory.
P1-134 Experimental Detection of Entanglement Polytopes via Local Filters
Yuanyuan Zhao, Markus Grassl, Bei Zeng and Guoyong Xiang
Abstract: Entanglement polytopes result in finitely many types of entanglement that can be
detected by only measuring single-particle spectra. With high probability, however, the local
spectra lie in more than one polytope, hence providing no information about the
entanglement type. To overcome this problem, we propose to additionally use local
filters. We experimentally demonstrate the detection of entanglement polytopes in a fourqubit system. Using local filters we can distinguish the entanglement type of states with the
same single particle spectra, but which belong to different polytopes.
P1-135 Computing Permanents for Boson Sampling on Tianhe-2 Supercomputer
Junjie Wu, Yong Liu, Baida Zhang, Xianmin Jin, Yang Wang, Huiquan Wang and Xuejun
Yang
Abstract: Boson sampling [1], a specific quantum computation problem, is widely regarded to
be one of the most achievable fields in which quantum machine will outperform the most
powerful classical computer in the near term, although up to now no upper-bound of how fast
the classical computers can compute matrix permanents, the core problem of Boson
sampling, has been reported. Here we test the computing of the matrix permanent on
Tianhe-2 [2], a supercomputer retaining its position as the world's No. 1 system for six times
since June 2013. We arrived at the time (about 77.41~112.44 minutes) to compute the
permanent of a 50×50 matrix in an acceptable precision. In addition, we have found that
Ryser's algorithm will produce an unacceptable error with the increase of problem scale,
compared to Balasubramanian-Bax/Franklin-Glynn's algorithm in the same complexity. The
precision issue suggests carefully check in future research of Boson sampling, and
comprehensive comparison between quantum computer and classical computer. More
details: arXiv1606.05836. [1] Aaronson, S. and Arkhipov, A. The computational complexity of
linear optics. In Proceedings of the Forty-third Annual ACM Symposium on Theory of
Computing, STOC '11, 333-342 (ACM, New York, NY, USA, 2011). [2] Liao, X et al.,
MilkyWay-2 supercomputer: system and application. Front. Comput. Sci. 8(3), 345-356, June
(2014).
77
P1-136 Universal optimal device-independent witnessing of quantum channels
Michele Dall'Arno, Sarah Brandsen and Francesco Buscemi
Abstract: Quantum process tomography, the standard procedure to characterize any
quantum channel in nature, is affected by a circular argument: in order to characterize the
channel, the tomographic preparation and measurement need in turn to be already
characterized. We break this loop by designing an operational framework able to optimally
characterize any given unknown quantum channel in a device-independent fashion, namely,
by only looking at its input-output statistics, under the sole assumption that quantum theory
is valid. We provide explicit solutions, in closed form, for practically relevant cases such as
the erasure, depolarizing, and amplitude-damping channels.
P1-138 Optimal communication via mixed quantum t designs
Sarah Brandsen, Michele Dall'Arno and Anna Szymusiak
Abstract: We operationally introduce mixed quantum t designs as the most general arbitraryrank extension of projective quantum t designs which preserves indistinguishability from the
uniform distribution for t copies. First, we derive upper bounds on the classical
communication capacity of any mixed t design measurement, for t in [1,5]. Second, we
explicitly compute the classical communication capacity of several mixed t design
measurements, including the depolarized version of: any qubit and qutrit symmetric,
informationally complete (SIC) measurement and complete mutually unbiased bases (MUB),
the qubit icosahedral measurement, the Hoggar SIC measurement, any anti-SIC (where
each element is proportional to the projector on the subspace orthogonal to one of the
elements of the original SIC), and the uniform distribution over pure effects.
P1-139 Surpassing the no-cloning limit with a heralded hybrid linear amplifier
Jing Yan Haw, Jie Zhao, Josephine Dias, Syed Assad, Mark Bradshaw, Rémi Blandino,
Thomas Symul, Tim Ralph and Ping Koy Lam
Abstract: The linearity of quantum mechanics dictates that it is impossible to generate
perfect clones of arbitrary quantum states. Associated with this restriction is the quantitative
`no-cloning limit' that sets an upper bound to the quality of the generated clones. Recently it
was suggested that by abandoning determinism, probabilistic methods could offer a way of
circumventing the no-cloning limit, enabling clones to have fidelity surpassing the no-cloning
limit. We report the first experimental demonstration of a probabilistic scheme of cloning
arbitrary quantum states that clearly surpasses the no-cloning limit. Our scheme is based on
a hybrid amplifier that combines an ideal deterministic linear amplifier with a heralded
measurement-based noiseless amplifier. We demonstrate the production of up to five clones
with the fidelity of each clone clearly exceeding the corresponding no-cloning limit. Because
successful cloning events are heralded, our scheme has the potential to be adopted in
quantum repeater, teleportation and computing applications.
78
P1-144 Generation and storage of multimode entangled light in a solid state, spinwave quantum memory
Kate Ferguson, Sarah Beavan, Jevon Longdell and Matthew Sellars
Abstract: Here we demonstrate generating and storing entanglement in a solid state, spinwave quantum memory with on-demand recall using the process of rephased amplified
spontaneous emission (RASE). Amplified spontaneous emission (ASE), resulting from an
inverted ensemble of Pr3+ ions doped into a Y2SiO5 crystal, generated entanglement
between the collective atomic state of the ensemble and the output optical field. The
ensemble was then rephased using a four-level echo technique. By violating the
inseparability criterion for continuous variables entanglement between the ASE and its echo
was confirmed when the RASE was stored as a spin-wave for up to 5 µs. In addition, RASE
was used to generate temporally multimode entanglement with almost perfect
distinguishability between two temporal modes demonstrated.
P1-145 Fast-gated single-photon counting
thermoelectrically cooled photomultiplier tube
Yanhui Cai, Zhengyong Li and Xiangkong Zhan
with
ultra-low
noise
based
on
Abstract: Single-photon detecting (SPD) and counting is a crucial technique in a large
number of areas such as quantum key distribution (QKD)[1,2], fluorescence laser scanning
microscopy[3], high-resolution light detection and ranging (LIDAR)[4]. Although many
schemes have been proposed to detect single photons up till now[2,5], it is a long way to
develop an ideal single-photon detector with both high efficiency and low noise which always
restrict each other. Recently, we establish a photon counting system using an ultra-low-noise
photomultiplier tube (PMT), and realize the SPD with high detection efficiency of 35% at 405
nm assisted with fast-gating technology. Removing the noise due to leakage, we have
discriminated the photonic signal at much smaller level with short interval of ~9 ns.
Furthermore, we develop a ultra-stable thermoelectric cooling system to reduce the dark
counts (DCs) generated in the PMT. Results show that the total DCs become smaller and
smaller as the temperature decreasing. At -20 degree and below, the net dark count will be
pretty close to zero, which is be on a par with the superconducting nanowire detectors.
This work is supported by the National Natural Science Foundation of China (Grant Nos.
11274037 and 11574026), the Program for New Century Excellent Talents in University,
MOE of China (Grant No. NCET-12-0765), and the Foundation for the Author of National
Excellent Doctoral Dissertation, China (Grant No. 201236).
References
[1] Peng CZ, Zhang J, Yang DC et al., Phys. Rev. Lett. 98, 010505 (2007)
[2] Scarani V, Bechmann-Pasquinucci H, Cerf N J, et al., Rev. Mod. Phys. 81, 1301–1350
(2009)
[3] Benninger R, Ashby W, Ring E and Piston D, Opt. Lett. 33, 2895–2897 (2008)
[4] Howland G, Lum D, Ware M and Howell J, Opt. Express 21, 23822–23837 (2013)
[5] Xu L L, Wu E, Gu X R, Jian Y, Wu G and Zeng H P, Appl. Phys. Lett. 94, 161106 (2009)
79
Abstracts – Posters (Tuesday)
P2-146 Kochen-Specker Theorem Proofs with Non-specific Projectors from Extended
KS Value Assignment Rules
Tang Weidong
Abstract: Since the enlightening proofs of quantum contextuality first established by Kochen
and Specker, and also by Bell --- known as Bell-KS theorem or simply KS theorem --- more
than half a century ago, various simplified and ingenious proofs have been presented to
terminate the non-contextual hidden variable(NCHV) arguments of our nature at a
microscopic scale. To show the conflict between the NCHV theory and quantum mechanics,
using Kochen-Specker(KS) sets of yes-no tests is a common way. Whereas, amid most of
the published proofs of KS theorem, the projectors in a KS set to form a direct logical
contradiction are specifically chosen. Here a method for mass production of the proofs, from
projectors in non-specific directions as the core part of the KS set to extract the contradiction
in a statistical manner, is proposed. It provides a more distinct understanding of KS theorem
from a geometric view.
P2-147 Arbitrary Multi-Qubit Generation
Farid Shahandeh, Austin P. Lund, Timothy C. Ralph and Michael R. Vanner
Abstract: An active field of research in quantum optics and quantum information is the
development of techniques for producing arbitrary quantum states of different physical
systems. This is by virtue of the broad range of applications including quantum computation
and communication, quantum simulation, and quantum metrology, that each need specific
quantum states as a resource. Here, we propose and analyse a scheme for single-railencoded arbitrary multi-qubit quantum state generation to provide a versatile tool for
quantum optics and quantum information applications. Our scheme can be realized, for
small numbers of qubits, with current technologies using single photon inputs, passive linear
optics, and heralding measurements. The particular examples of two- and three-qubit cluster
states are studied in detail. We show that such states can be prepared with a high probability
of success. Our analysis quantifies the effects of experimentally relevant imperfections and
inefficiencies. The general case of arbitrary $N$-qubit preparation is discussed and some
interesting connections to the boson sampling problem are given.
P2-148 Generation of photon pairs in a nonlinear waveguide array with
inhomogeneous poling pattern
Francesco Lenzini, James Titchener, Sachin Kasture, Alexander N. Poddubny, Andreas
Boes, Ben Haylock, Paul Fisher, Matteo Villa, Arnan Mitchell, Alexander S. Solntsev, Andrey
A. Sukhorukov and Mirko Lobino
Abstract: We propose and experimentally demonstrate a nonlinear waveguide array with
inhomogeneous poling pattern designed for the generation of photon pairs. This device
deterministically separates the generated photon pair in two different spatial modes while
keeping the pump in a separate waveguide. The biphoton wavefunction produced from the
device is characterized by employing a novel method based on reversed sum-frequency
generation measurements.
80
P2-149 Geometry of system-bath coupling and gauge fields: manipulating currents
and driving phase transitions
Chu Guo and Dario Poletti
Abstract: Quantum systems in contact with an environment display a rich physics emerging
from the interplay between dissipative and Hamiltonian terms. We consider a dissipative
boundary driven ladder in presence of a gauge field which can be implemented with ion
microtraps arrays. The dissipation stimulates currents while the gauge field tends to steer
the flow. We show that depending on the geometry of coupling to the baths and of the
strength of the gauge field, non-equilibrium phase transitions emerge strongly modifying the
currents both in magnitude and spatial distribution. This work shows how quantum
simulations can be used to pave the way towards new ways of controlling energy and heat
flow in nano and quantum systems. An extended abstract is attached.
P2-150 Hong-Ou-Mandel interference between two collective excitations
Jun Li, Ming-Ti Zhou, Xiao-Hui Bao and Jian-Wei Pan
Abstract: Single collective excitations in one atomic ensemble have been widely used to
store single photons, harnessing the enhanced atom-light coupling. By creating and
manipulating more distinct excitations, one atomic ensemble may encode many qubits and
become a promising platform for quantum computing and quantum simulation. Here we
generate two distinct collective excitations in a deterministic fashion via Rydberg blockade
and realize the Hong-Ou-Mandel interference between them. These two excitations occupy
different Zeeman levels, and a beam-splitter operation is performed via stimulated Raman
transitions. By converting the excitations into single photons and performing coincidence
detection, a high two-excitation interference visibility is measured. Moreover, the interference
results in an entangled NOON state for two excitations, which is two times more sensitive to
the magnetic field, compared with a single excitation. A straight-forward extension of our
experiment may realize Bose sampling with multiple excitations in a collective fashion.
P2-151 Nonlinear infrared spectrometer free from spectral selection
Anna Paterova, Shaun Lung, Dmitry Kalashnikov and Leonid Krivitsky
Abstract: Nonlinear interference of parametric down conversion (PDC) allows simultaneous
measurements of real and imaginary parts of the refractive index in the infrared (IR) range
using visible range optics and detectors [1]. However, the method still requires spectral and
spatial selection. Here we present a special arrangement of the interferometer, which allows
eliminating this requirement and results in the increased sensitivity and throughput.
P2-152 Secret key agreement demonstration over 7.8 km free-space optical channel
Mikio Fujiwara, Toshiyuki Ito, Mitsuo Kitamura, Hiroyuki Endo, Morio Toyoshima, Hideki
Takenaka, Yoshihisa Takayama, Ryosuke Shimizu, Masahiro Takeoka, Ryutaroh
Matsumoto and Masahide Sasaki
Abstract: Security in free-space (wireless) communication is an important issue in modern
communication networks. Recently, secret key agreement between two terminals by
exploiting the physical properties of a channel has attracted much attention. This includes
quantum key distribution (QKD) as an extremely secure case in which an eavesdropper’s
power is only limited by law of physics. In these scenarios, a sender (Alice), a legitimate
receiver (Bob), and an eavesdropper (Eve) share correlated information through a broadcast
81
channel (called a wiretap channel) from Alice to Bob and Eve, and then exchange messages
over a public channel to establish a key between Alice and Bob which is secure against Eve.
While QKD provides the ultimate security, its operation distance and capacity are limited.
One of the natural direction is thus to compromise Eve’s power with practically reasonable
assumptions. The reasonability may highly depend on a real condition of each
communication scenario. To explore such an issue from an experimental side in the freespace optical link scenario, we construct a line-of-sight free-space optical link system in
which two receiver terminals are installed on Tokyo Free-space optical link shown in Fig.1.
One of the receiver terminals works as Eve’s terminal to estimate the maximum information
leakage ratio in a practical situation. By using this system, we succeed in demonstrating the
secret key agreement protocol over 7.8 km free-space optical channel with eye safe
wavelength region. The secure key rate depends on a weather condition, however, 7 M bit/s
is obtained. Our experimental result can contribute for further feasibility discussions on
implementing a physical layer secret key agreement in free-space optical link as well as for
free-space QKD since while our experiment is operated in classical region, the experimental
observation of the free-space channel properties in weak laser power regime could be useful
for estimating the feasibility of future free-space QKD links.
P2-153 Interferometric Resolution of Incoherent Optical Point Sources near the
Quantum Limit
Ranjith Nair and Mankei Tsang
Abstract: We propose and analyze an interferometric system for estimating the separation
between thermal point sources well below the Rayleigh limit. Monte-Carlo simulations
demonstrating the superresolution effect are also presented.
P2-155 Efficient Large Block Codes Ancilla States Preparation for Fault-tolerant
Quantum Computation
Yi-Cong Zheng, Ching-Yi Lai and Todd Brun
Abstract: Fault-tolerant quantum computation (FTQC) schemes using multi-qubit large block
codes require a huge amount of clean ancilla states of different types with weak error
correlation inside each block. These ancilla states are usually logical stabilizer states of the
data code blocks, which are generally difficult to prepare if code size is large. Meanwhile, the
yield rate of preparation process are typically extremely low when the distance of block code
is large. Here, we propose a protocol to distill various of ancilla states necessarily for FTQC
fault-tolerantly using classical codes. Analytical analysis shows that correlated errors can be
largely removed. At the same time, the yield rate can be high for general large block code
with arbitrary size, using proper classical codes. Numerical Monte-Carlo simulation based on
[[23,1,7]] quantum Golay code and quantum [[127, 57, 11]] support this conclusion with
reasonably low gate error rates.
P2-156 Multi-photon experiments with solid-state single-photon sources
Marcelo Pereira de Almeida, Juan Carlos Loredo, Tau Bernstorff Lehmann, Nor Azwa
Zakaria, Paul Hiliare, Isabelle Sagnes, Aristide Lemaitre, Pascale Senellart and Andrew
White
Abstract: Multi-photon experiment with solid-state single-photon sources
Solid-state emitters, such as semiconductor quantum dots, are a promising platform for
single-photon sources. Recent breakthroughs in material syntheses and fabrication
82
processes have enabled a new generation of devices, which combine high emission
brightness with a near unity indistinguishable pure single-photon output.
We will present our work towards developing and employing quantum dot single-photon
sources to realise quantum-based technologies. We will focus on devices consisting of a
single quantum dot deterministically coupled to a micro-pillar cavity. The enhanced
spontaneous emission due to Purcell factors available in these devices, result in a bright
single-photon output [1,2]. Here we demonstrate solid-state photon sources with an absolute
brightness at the output of a single-mode finer of 14% and purities up to 99% [3].
We also consider the temporal behaviour of the single-photon indistiguishability. We show
that photons emitted with temporal separation as high as 400s display two-photon quantum
interference [3]. We will discuss how this property can be used in experiments requiring
multiple indistinguishable single-photons. Finally we present our preliminary results
employing 2, 3 and 4 single-photons to realise optical entangling circuits [4] and qubit fusion
operations, as well as to demonstrate quantum algorithms, in particular the Boson Sampling.
[1] O. Gazzano et al., Nat. Comm. 4, 1425 (2013).
[2] Somaschi, N., Giesz, V., Santis, L. De, Loredo, J. C., Almeida, M. P.,
et al., arXiv:1510.06499 (2015).
[3] Loredo, J. C., Zakaria, N. A., Somaschi, N., Anton, C., Santis, L. De, Giesz, V., Grange,
T., Broome, M. A., Gazzano, O., Coppola, G., Sagnes, I., Lemaitre, A., Auffeves, A.,
Senellart, P., Almeida, M. P., White, A. G., arXiv:1601.00654 (2016).
[4] Gazzano, O., Almeida M. P., et al., Phys. Rev. Lett. 110, 250501 (2013).
P2-157 Violation of steering inequality with path entangled single photon
Anthony Martin, Thiago Guerreiro, Fernando Monteiro, Jonatan Bohr Brask, Tamás Vertési,
Boris Korzh, Felix Bussieres, Varum Verma, Adriana Lita, Richard Mirin, Saewoo Nam,
Francesco Marsili, Matthew. Shaw, Nicolas Gisin, Nicolas Brunner, Hugo Zbinden and
Abstract: Here we report the violation of quantum steer- ing inequality by a single-photon
entanglement via displacement-based measurements.
P2-158 Experimental Demonstration of Continuous Variable One Sided Device
Independence
Nathan Walk, Sara Hosseini, Jiao Geng, Oliver Thearle, Jing Yan Haw, Seiji Armstrong,
Syed M. Assad, Jiri Janousek, Timothy C. Ralph, Thomas Symul, Howard Wiseman and
Ping Koy Lam
Abstract: For continuous variable quantum key distribution (CV QKD) a new key rate that is
one sided device independent (1sDI) has been found based on the Gaussian family of
protocols. The new key rate has been derived from a recently found entropic uncertainty
relation. The new key rate shows a close relationship with steering. With the new key rate
we have attempted to demonstrate five of a possible six 1sDI protocols. Three of these
yielded a positive key. The first two were Entanglement based protocols and the third was a
prepare and measure scheme.
83
P2-160 Detector-device-independent quantum key distribution
Anthony Martin, Alberto Boaron, Boris Korzh, Charles Lim, Gianluca Boso, Raphael
Houlmann and Hugo Zbinden
Abstract: To prevent all known and yet-to-be-discovered detector side-channel attacks, a
measurement-device-independent QKD (mdi- QKD) protocol was proposed [2]. In this
scheme, Alice and Bob each randomly prepare one of the four Bennett & Brassard (BB84)
states and send it to a third party, Charlie, whose role is to introduce entanglement between
Alice and Bob via a Bell- state measurement (BSM). Alice and Bob do not have to trust
Charlie since any other non-entangling measurement would necessarily introduce some
noise between them. Unfortunately, mdiQKD possesses many drawbacks. Firstly, the
achievable se- cure key rates (SKR) are significantly lower compared to conventional
prepare and measure (P&M) QKD systems [3, 4]. This is mainly because a two-photon BSM
relies on coincidence detections, which sets stringent requirements on the detector
efficiency. Another factor is that a two-photon BSM implemented with linear optics is at most
50% efficient and, when using WCSs, the results from one of the bases cannot be used for
the raw-key generation due to an inherent 25% error rate [5, 6]. Furthermore, the resource
overhead in the finite-key scenario [7] is significantly larger compared to common P&M
schemes [4, 8]. Finally, the technological complexity of mdiQKD is greater due to the use of
two-photon interference, requiring both photons to be indistinguishable in all degrees of
freedom (DOFs) : temporal, polarization and frequency.
We have recently proposed a QKD scheme that overcomes the aforementioned limitations
but is still secure against all detector side-channel attacks [9]. This bridges the gap between
the superior performance and practicality of P&M QKD schemes and the enhanced security
offered by mdiQKD. Our scheme, referred to as detector- device-independent QKD
(ddiQKD), essentially follows the idea of mdiQKD, however, instead of encoding separate
qubits into two independent photons, we exploit the concept of a two-qubit single-photon
(TQSP).
P2-161 Heralded hybrid noiseless linear amplifier for arbitrary coherent states
Jie Zhao, Josephine Dias, Jing Yan Haw, Mark Bradshaw, Remi Blandino, Thomas Symul,
Timothy Ralph, Ping Koy Lam and Syed Assad
Abstract: As a direct consequence of the linearity and unitarity of quantum mechanics,
phase-insensitive linear amplifiers inevitably suffer some amount of signal-to-noise (SNR)
degradation. Recently, it was conceived theoretically and demonstrated experimentally that
by forgoing determinism, benefits of noiseless linear amplification could be extracted, though
at the detriment of success probability. Here we report a heralded hybrid linear amplifier
(HLA) for arbitrary coherent states that overcomes the noise penalty with only linear optical
elements. Such HLA, comprising of the ideal linear amplifier and the measurement-based
noiseless linear amplifier, allows one to trade off between the SNR and the success
probability flexibly. Given an arbitrary input coherent state, both amplification gains and
truncations are freely tunable to optimise the success probability while preserving the input
Gaussianity. We report an output SNR up to 1.53 times that of the input, which provides a
clear demonstration of a noiseless linear amplifier working nondeterministically.
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P2-162 Quantum teleportation by quantum walks
Yun Shang
Abstract: It is well-known that the preparation of entangled pairs and joint measurement
necessary for quantum teleportation are very difficult to realize in experiments. Is it possible
to avoid the above two hurdles in quantum teleportation? Based on quantum walks, a novel
scheme of quantum teleportation is developed to relax these hurdles. This scheme does not
require the preparation of an entangled state as a source beforehand, and the main
resources are only two shift operators. For the case of an unknown qubit state, two steps of
quantum walks can be enough for teleportation. However, completely unlike complex joint
measurement in original teleportation scheme, the proposed scheme just needs local
measurement. For the case of $n$-dimensional states, quantum walks on graphs can be
used to teleport. However, comparing the cost of measurement basis with Bennet \emph{et
al.}'s scheme, only two $n$ dimensional measurement bases are needed, rather than one
$n^{2}$ dimension measurement basis. These factors can help effectively decrease the
error problem and potentially lead to faster, more reliable quantum computation.
P2-163 Characterizing ground and thermal states of few-body Hamiltonians
Otfried Guehne and Felix Huber
Abstract: We provide methods to characterize the states generated by two- and, more
generally, k-body Hamiltonians as well as the convex hull of these sets. This leads to new
insights into the question which states are uniquely determined by their marginals and to a
generalization of the concept of entanglement. Finally, certification methods for quantum
simulation can be derived.
P2-164 Classical realization of “quantum-optical coherence tomography” by timeresolved pulse interferometry
Kazuhisa Ogawa and Masao Kitano
Abstract: Quantum-optical coherence tomography (Q-OCT) provides a dispersion-canceled
axial-imaging method, but its practical use is limited by the weakness of the light source and
by artifacts in the images. A recent study using chirped-pulse interferometry (CPI) has
demonstrated dispersion-canceled and artifact-free OCT with a classical system; however,
unwanted background signals still remain after removing the artifacts. Here, we propose a
classical optical method that realizes dispersion-canceled, artifact-free, and background-free
OCT. This OCT method uses time-resolved pulse interferometry (TRPI), which we proposed
to achieve dispersion-canceled OCT with a classical system. We have also introduced a
subtraction method to remove artifacts and background signals. With these methods, we
experimentally demonstrated dispersion-canceled, artifact-free, and background-free axial
imaging of a coverglass and cross-sectional imaging of the surface of a coin.
P2-165 Distribution of quantum coherence in multipartite systems
Chandrashekar Radhakrishnan, Manikandan Parthasarathy, Segar Jambulingam and Tim
Byrnes
Abstract: The distribution of coherence in multipartite systems is examined. We use a new
coherence measure with entropic nature and metric properties, based on the quantum
Jensen-Shannon divergence. The metric property allows for the coherence to be
decomposed into various contributions, which arise from local and intrinsic coherences. We
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find that there are trade-off relations between the various contributions of coherence, as a
function of parameters of the quantum state. In bipartite systems the coherence resides on
individual sites or distributed among the sites, which contribute in a complementary way. In
more complex systems the characteristics of the coherence can display more subtle
changes with respect to the parameters of the quantum state. In the case of the XXZ
Heisenberg model, the coherence changes from a monogamous to a polygamous nature.
This allows us to define the shareability of coherence, leading to monogamy relations for
coherence.
P2-166 Effects of measurement dependence on generalized CHSH-Bell test in the
single-run and multiple-run scenarios
Dan-Dan Li, Yu-Qian Zhou, Fei Gao, Xin-Hui Li and Qiao-Yan Wen
Abstract: Bell tests, as primitive tools to detect nonlocality in bipartite systems, rely on the
major assumption — measurement independence. Since ensuring measurement
independence in a practical Bell test is extremely difficult, it is crucial to explore effects of
relaxing the assumption. Recently, in the simplest CHSH-Bell test, D. E. Koh et al. [Phys.
Rev. Lett. 109, 160404 (2012)] builded the relation between measurement dependence and
the maximum value of CHSH-Bell correlation function that an adversary (Eve) can fake. As
well, J. E. Pope et al. [Phys. Rev. A 8, 032110 (2013)] and X. Yuan et al. [Phys. Rev. A 91,
032111 (2015)] settled the same problem in the multiple-run scenario with the general input
distribution and the factorizable one, respectively. While, pertinent results in generalized
CHSH-Bell test is still missing. Here, we study this problem and establish the relation among
measurement dependence, guessing probability and the maximum value of generalized
CHSH-Bell correlation function. Furthermore, we also consider the multiple-run scenario and
show the relations in both input distributions. Interestingly, compared with the simplest
CHSH-Bell test, we find that it is more difficult for Eve to fake a violation in generalized
CHSH-Bell test under some
special cases.
P2-167 High fidelity entanglement swapping via a time-resolved coincidence
measurement
Yoshiaki Tsujimoto, Motoki Tanaka, Yukihiro Sugiura, Rikizo Ikuta, Shigehito Miki, Taro
Yamashita, Hirotaka Terai, Takashi Yamamoto, Masato Koashi and Nobuyuki Imoto
Abstract: We experimentally demonstrated high fidelity entanglement swapping using two
polarization-entangled photon pairs generated by spontaneous parametric down conversion
(SPDC) pumped by continuous-wave (cw) light via a time-resolved coincidence
measurement. The two entangled photon pairs are generated by cw-pumped SPDC through
a periodically poled lithium niobate waveguide in a Sagnac configuration and they were
sufficiently narrowed by interference filters with the central wavelengths 1541 nm and 1580
nm. The time-resolved photon detection is achieved by superconducting nanowire singlephoton detectors with low timing jitter. After performing the Bell-state measurement on the
two photons at 1541 nm, we performed the quantum state tomography on the remaining two
photons at 1580 nm. The observed fidelity of the two photons to the maximally entangled
state was 0.84 $\pm$ 0.04.
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P2-168 Quantum metrology using topological quantum states.
Tim Byrnes
Abstract: One of the standard ways to obtain a quantum enhancement for precision
measurements is to use entanglement in the system to reduce quantum noise. This allows
for obtaining a square root enhancement approaching the Heisenberg limit going beyond the
standard quantum limit. Here we discuss a different approach for obtaining a quantum
enhancement using topological states. As is well known, the electrical quantum Hall effect
can measure the unit of conductance extremely precisely, to a level in the region of 10^-10
in relative error. This is due to the Hall resistance being a topological quantity, and is robust
to imperfections. We apply this same idea to measuring the mass of atoms in Bose-Einstein
condensates (BEC) using vortices. By displacing a vortex in a BEC, this gives rise to a
Magnus force, which in turn creates a current in the BEC. The current is related to the
transverse population difference as a topological quantity. This gives rise to an analogue
quantum Hall effect in BECs, which should be readily observable using existing experimental
techniques. Instead of quantization in units of e/h, this gives quantization in units of m/h,
where m is the mass of the atoms. Measuring the mass of atoms very precisely gives the
possibility of a novel definition of the standard of the kilogram in terms of a fixed number of
atoms. The kilogram is the last SI unit that is still defined in terms of a material artifact (the
IPK). Currently only the relative mass of an atom can be precisely measured, and not the
absolute mass. If a precise measurement of an atom can be made this potentially could
contribute to a way of defining the standard of mass quantum mechanically. This is in
contrast to other methods which are based primarily on classical techniques.
P2-169 Ultrafast coherent control of Bose-Einstein condensates using stimulated
Raman adiabatic passage
Andreas Thomasen and Tim Byrnes
Abstract: Bose-Einstein condensates have been proposed for a variety of quantum
information tasks including quantum simulation, metrology and information processing. Their
attractiveness in these applications is partly due to the fact that physical interactions are
boosted by the occupation number of a BEC. For instance, dipole transition matrix elements
exhibit an order of N dependence, which is a good reason to expect that speedups in
coherent control are possible. Furthermore, cold atoms are well known to coherently store
quantum memories with long lifetimes. If both these aspects of cold atomic BECs can be
harnessed for quantum computing, one may bridge a gap in between platforms that are
useful for storage purposes and those that perform very fast operations (e.g.
superconducting circuits, etc.) However, using BECs for these tasks is not without
difficulties. Spontaneous emission terms appear in the equations of motion of a BEC
proportional to the number of particles squared. Thus, even slight leakage into the excited
states of a BEC has serious consequences for the fidelity of any operations performed on it.
We propose a novel scheme for performing arbitrary unitary operations on two-component
rubidium 87 BECs using stimulated Raman adiabatic passage (STIRAP). STIRAP is a
technique for population transfer in quantum systems that avoids excitation of bright states.
It does so by effecting a transfer exclusively through adiabatic evolution of the dark
eigenstate manifold of a slowly evolving Hamiltonian. In this way it becomes possible to
completely avoid spontaneous emission as long as the adiabatic condition is adhered to. Our
scheme assumes that BECs have been magnetically trapped with a preference for first-order
Zeeman insensitive hyperfine ground levels. It is thus readily implementable by
experimenters. Through simulations we obtain fidelities greater than 99.9% when the
operation is applied for 27.7 ns on a BEC containing 1000 atoms.
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P2-170 Generation and non-destructive detection of single microwave photons
Sankar Raman Sathyamoorthy
Abstract: In this poster, we show how to use superconducting qubits at the end of a semiinfinite transmission line, analogous to atoms in front of a mirror, to generate and detect
microwave photons. We present two simple and efficient schemes to generate a single
photon on demand from a coherent pi pulse using the atom in front of a mirror, along with
either a beam splitter or by using tunable coupling [1]. The frequency of the emitted photon
can be tuned by tuning the level splitting of the qubit and the single photon wave-packets
can be shaped in time. The presented schemes are relatively insensitive to dephasing and
can be extended to generate correlated and entangled photons. They can also be used to
generate photonic superposition states between 0 and 1 in arbitrary wave packets.
We also present a scheme to non-destructively detect a propagating microwave photon by
using the strong effective photon-photon interaction mediated by the artificial atom. We show
that by cascading atoms, we can increase the measurable signal beyond the vacuum noise,
leading to signal to noise ratio for photon detection above 1 [2]. The single photon to be
detected survives the interactions making the scheme QND in photon number.
References:
[1] S. R. Sathyamoorthy, A. Bengtsson, S. Bens, M. Simoen, P. Delsing, G. Johansson,
arXiv:1511.03038 (2015)
[2] S. R. Sathyamoorthy, L. Tornberg, A. F. Kockum, B. Q. Baragiola, J. Combes, C. M.
Wilson, T. M. Stace, and G.Johansson, Phys. Rev. Lett. 112, 093601 (2014).
P2-171 A correlation based entanglement criterion in bipartite multi-boson systems
Wiesław Laskowski, Marcin Markiewicz, Danny Rosseau, Tim Byrnes, Kamil Kostrzewa and
Adrian Kołodziejski
Abstract: We describe a criterion for the detection of entanglement between two multi-boson
systems. The criterion is based on calculating correlations of Gell-Mann matrices with a fixed
boson number on each subsystem. This applies naturally to systems such as two entangled
spinor Bose-Einstein condensates. We apply our criterion to several experimentally
motivated examples, such as an SzSz entangled BECs, ac Stark shift induced two-mode
squeezed BECs, and photons under parametric down conversion. We find that
entanglement can be detected for all parameter regions for the most general criterion.
Alternative criteria based on a similar formalism are also discussed together with their
merits.
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P2-172 On the equivalence of separability and extendability of quantum states
K. R. Parthasarathy, Ritabrata Sengupta and B. V. Rajarama Bhat
Abstract: Motivated by the notions of k-extendability and complete extendability of the state
of a finite level quantum system as described by Doherty et al (Phys. Rev. A, 69:022308),
we introduce parallel definitions in the context of Gaussian states and using only properties
of their covariance matrices derive necessary and sufficient conditions for their complete
extendability. It turns out that the complete extendability property is equivalent to the
separability property of a bipartite Gaussian state. Following the proof of quantum de Finetti
theorem as outlined in Hudson and Moody (Z.Wahrscheinlichkeitstheorie und Verw. Gebiete,
33(4):343--351), we show that separability is equivalent to complete extendability for a state
in a bipartite Hilbert space where at least one of which is of dimension greater than 2. This,
in particular, extends the result of Fannes, Lewis, and Verbeure (Lett. Math. Phys. 15(3):
255--260) to the case of an infinite dimensional Hilbert space whose C* algebra of all
bounded operators is not separable. Latest version of this paper can be seen in arXiv:
http://arxiv.org/abs/1601.02365
P2-173 Evaluation of quantum 1D repetition codes’ performance against quantum
noise
Takanori Sugiyama, Keisuke Fujii, Haruhisa Nagata and Fuyuhiko Tanaka
Abstract: As error rates of quantum gates implemented in recent experiments approach a
fault-tolerant threshold for a depolarizing noise model, it becomes more important to
investigate performance of quantum error correction codes against more general and
realistic noise models. The standard approach assuming depolarizing noise models is not
realistic and can overestimate the performance. On the other hand, a rigorous approach with
the diamond norm is applicable to realistic noise models but greatly underestimates the
performance. Here we propose a new theoretical framework for evaluating performances of
quantum error correction codes, which is applicable to any local noise models. We apply the
method to a quantum 1D repetition code, and numerically evaluate the performance with 9 to
61 physical qubits. Our numerical results clarify the effect of quantum coherence in noise on
the performance of quantum 1D repetition codes.
P2-174 Monolithically integrated optics for scalable trapped-ion single-photon
sources
Mirko Lobino, Mojtaba Ghadimi, Valdis Blums, Benjamin G. Norton, Paul Fisher, Harley
Hayden, Jason Amini, Curtis Volin, Dave Kielpinski and Erik W Streed.
Abstract: We demonstrate the first ion chip trap with fully integrated and scalable diffractive
mirrors. We realize high efficiency collection, gathering 5.81(0.84)% total ion light collection
and coupling 2.41 (0.89)% of total ion light into a single mode fiber.
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P2-175 Detection-dependent six-photon NOON state interference
Rui-Bo Jin, Mikio Fujiwara, Ryosuke Shimizu, Robert Collins, Gerald Buller, Taro Yamashita,
Shigehito Miki, Hirotaka Terai, Masahiro Takeoka and Masahide Sasaki
Abstract: We have experimentally demonstrated and analyzed theoretically six-, four- and
two-photon interference from a NOON state emitted by a spontaneous parametric down
conversion source detected using six superconducting nanowire single-photon detectors. It
was found that the coherence time, visibility and shape of the interference patterns are
strongly dependent on the detection schemes. This is the first experimental observation of
detection dependency of NOON state interferometry with up to six photons at telecom
wavelengths. The results of this experiment and the theoretical analysis will find applications
in analytical approaches which are based on the envelope of the NOON state interference
pattern.
P2-176 Stationary Light in Resonant and Far-Detuned Atom-Optic Memories
Jesse Everett, Geoff Campbell, Young-Wook Cho, Pierre Vernaz-Gris, Daniel Higginbottom,
Olivier Pinel, Nick Robins, Ping Koy Lam and Ben Buchler
Abstract: Stationary light (SL) describes light that has been stopped but not entirely
absorbed into an atomic ensemble. SL is one possible method for enhancing incredibly weak
nonlinear interactions between single photons. Stationary light has previously been
demonstrated with electromagnetically-induced transparency (EIT). In EIT, light resonant
with an atomic transition passes slowly through an atomic ensemble with the assistance of a
separate optical field – a control field. The control field couples the excited state to a second
ground state, preventing spontaneous emission and generating a coherent atomic
polarisation, or spinwave. The light propagates along with the spinwave, and by sending two
counter-propagating control fields, the spinwave is pushed in both directions, and the light is
effectively trapped in the atoms. Using an optically dense, elongated MOT of 87Rb, we
observe directly the behaviour of EIT-SL. Due to a large optical depth, we are able to confine
a pulse in a small region of the MOT. We image the spinwave from the side, perpendicular to
the direction of propagation, and are even able to push it back and forth by changing the
ratio of the control field intensities. We demonstrate that the propagation of EIT-SL can be
described by a simple equation. We also present a novel form of stationary light. Operating
in the Raman regime, where the light is far detuned from the atomic transition, the light
travels quickly through the memory. The control field causes the light to be coherently
absorbed into and re-emitted from the atoms. Because the light is not confined to the
spinwave, a different mechanism leads to the creation of stationary light. By using counterpropagating control fields with carefully chosen angles and frequencies and a specific shape
of spinwave, the light generated destructively interferes at each end of the atomic ensemble.
The system does not evolve, due to a destructive interference between light travelling in
opposite directions coupling into the spinwave. Thus, a strong stationary optical field is
generated. The condition for Raman-SL behaviour is that the spinwave integrates to zero
over the length of the ensemble. A spinwave that does not satisfy this condition rapidly
evolves to one that does. To experimentally test this theory, we write the spinwaves in a
gradient echo memory and send the counter-propagating control fields. Imaging the
spinwave gives additional information about the evolution of the spinwave, confirming the
stationary light and the rapid evolution of non-stationary spinwaves. We show that the
possible enhancement of nonlinear interaction scales in the same way for EIT-SL and
Raman-SL. we propose an experimentally realisable scheme by which useful nonlinear
interactions can be generated in the far-detuned system. The optical field of SL is used to
AC-Stark shift the energy of an atomic level on which another pulse is stored, generating a
90
measurable phase shift of the second pulse. We are currently pursuing experimental
evidence of these interactions.
P2-177 Particle-Indistinguishability Signatures in Phase Space
Farid Shahandeh
Abstract: Particle indistinguishability imposes entanglement on the states of identical
particles via the (anti)symmetrisation postulate. Such a fluffy bunny entanglement, however,
is considered to be unphysical and inaccessible. In Peres words "no quantum prediction,
referring to an atom located in our laboratory, is affected by the it mere presence of similar
atoms in remote parts of the universe."
Here, we consider the possibility of any observable effects due to particle indistinguishability
on the quantum phase-space representation of bosonic particles. We order the amount of
nonclassicality of the Wigner function and particle indistinguishability in a bipartite system of
n identical boson particles and prove that, regardless of the known classical and quantum
correlation contents of the state, redistributing particles between the two modes always
changes both quantities in an equivalent way, unambiguously representing the connection
between phase-space nonclassicality and quantum particle indistinguishability.
P2-179 Temporal multimode storage of entangled photons
Peter C. Strassmann, Alexey Tiranov, Jonathan Lavoie, Nicolas Brunner, Marcus Huber,
Varun B. Verma, Sae Woo Nam, Richard P. Mirin, Adriana E. Lita, Francesco Marsili, Mikael
Afzelius, Félix Bussières, Nicolas Gisin
Abstract: For practical optical quantum communication and computation based on the
quantum repeater scheme, time-division multiplexing significantly increases the probability of
success. An approach based on atomic ensembles and linear optics requires the ability to
store multiple temporal modes inside the quantum memory. [1]
Here we demonstrate the storage and release of at least 8 temporal modes in an atomic
frequency comb (AFC) [2] solid-state quantum memory, where at least two of the modes
contain a single photon. Each of the two stored photons (at 883 nm) is polarizationentangled with a partner photon at a telecom wavelength, i.e. two entanglement bits (ebits)
are stored simultaneously.
To certify the entanglement of the two pairs we develop and apply a new entanglement
witness. The novel entanglement witness is compatible for the experiments with the limited
number of detectors and is more efficient than the general quantum tomographic approach.
Our work is the first direct demonstration of storage of multiple pairs of entangled photons
using different temporal modes. This experiment proves that the temporal multiplexing in the
same spatial mode of quantum memories can be achieved for the entangled photon pairs
and opens a way for further developments to build a quantum repeater.
[1] Sangouard, N. et al. Quantum repeaters based on atomic ensembles and linear optics,
Rev. Mod. Phys. 83, 33-80 (2011).
[2] Afzelius, M. et al. Multimode quantum memory based on atomic frequency combs, Phys.
Rev. A 79, 052329 (2009).
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P2-180 Au Microdisk-Size Dependence of Quantum Dot Emission from the Hybrid
Metal-Distributed Bragg Reflector Structures Employed for Single Photon Sources
Baoquan Sun
Abstract: We investigate metallic microdisk-size dependence of quantum dot (QD)
spontaneous emission rate and microantenna directional emission effect for the hybrid
metal-distributed Bragg reflector structures based on a particular single QD emission. It is
found that the measured photoluminescence (PL) intensity is very sensitive to the size of
metallic disk, showing an enhancement factor of 11 when the optimal disk diameter is 2
micrometer and the numerical aperture of microscope objective NA=0.5. It is found that for
large metal disks, the Purcell effect is dominant for enhanced PL intensity, whereas for small
size disks the main contribution comes from plasmon scattering at the disk edge within the
light cone collected by the microscope objective.
P2-182 Quantum Carburettor Effect for Photon Number Shiftin
Jennifer Radtke, John Jeffers and Daniel Oi
Abstract: The quantum carburettor effect is an elegant, experimentally feasible
demonstration of the bosonic nature of light. Here we use this effect with conditional
measurement to implement the Susskind-Glogower photon number shifting operator, a nonGaussian operation with potential applications in continuous variable quantum information
processing.
P2-183 Noise-tolerant post-selected measurement using noise margin with GKP code
state
Kosuke Fukui, Akihisa Tomita and Atsushi Okamoto
Abstract: We propose a method for highly reliable measurement with GKP code states by
introducing noise margin. We use a hybrid quantum information processing where qubit
degrees of freedom for logical level are combined with quantum continuous variables for
enhancing noise resistance. As a simple example to show the validity of our proposal, we
applied for entanglement distribution and the results of numerical calculations confirm the
improvement of error rate using reasonable resources. This newly discovered property which
is different from discrete variables opens up potential for quantum information processing in
a continuous variable.
P2-184 An Optimal Design for Universal Multiport Interferometers
William Clements, Peter Humphreys, Benjamin Metcalf, Steven Kolthammer and Ian
Walmsley
Abstract: Linear optical quantum interferometry is a general framework that encompasses
any experiment that produces quantum states of light in several modes, interferes these
modes, and performs quantum measurements on them. It has been extremely successful as
a platform to study the foundations of quantum mechanics [1], perform quantum-enhanced
optical metrology [2], and demonstrate the principles of quantum simulation and universal
quantum computation [3]. However, building large optical interferometers that provide highfidelity interference is a challenge. Recently, reconfigurable universal photonic circuits, that
can implement any unitary transformation between several optical spatial modes, have
emerged as a powerful tool to provide this interference in chip-scale devices. They have
already been used to demonstrate a wide range of experiments, with interference between
up to six modes [4]. Their design is based on the seminal work by Reck et al [5], who
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showed that such universal circuits can be implemented by a specific planar triangular array
of 2x2 beam splitters and phase shifters, which are programmed using a simple analytical
method. However, this 20-year old design does not make use of the minimum possible
space on a planar substrate, nor does it have the most robust performance with respect to
component imperfections. In this sense, the design by Reck et al is not optimal. We present
a new design for universal photonic circuits, based on an alternative arrangement of beam
splitters and phase shifters, which outperforms the Reck design in several respects. This
design occupies half the physical footprint of the Reck design, which will allow larger and
lower-loss circuits to be built on integrated chips. I will also show that the optical
transformation implemented by devices built according to our design is much more robust to
imperfections such as unbalanced loss within the circuit. I will present a new decomposition
of a unitary matrix into 2x2 elements representing beam splitters, which we use to
straightforwardly program all the optical elements in the circuit to achieve the intended
transformation. We will also introduce our own recent experimental efforts to realise the
construction of this optimal device using a silica-based waveguide circuit. This compact and
loss tolerant design for fully programmable universal photonic devices will be of great
interest to anyone interested in building experimental reconfigurable linear optical circuits.
The new unitary matrix decomposition method that is used to program these circuits will also
be useful for other quantum systems, for example for ion traps [6] and superconducting
circuits [7]. More details about this work will be made available in a forthcoming ArXiv
preprint, named “An Optimal Design for Universal Photonic Circuits”. The authors of this
preprint have also jointly filed a patent for this work.
P2-186 Wavelength Conversion of non-classical light from rubidium atoms to the
telecom band
Rikizo Ikuta, Toshiki Kobayashi, Kenichiro Matsuki, Shigehito Miki, Taro Yamashita, Hirotaka
Terai, Takashi Yamamoto, Masato Koashi, Tetsuya Mukai and Nobuyuki Imoto
Abstract: We Observed non-classical telecom light which has a correlation with cold
rubidium atoms. In the experiment, the light at 780 nm was prepared from the rubidium
atomic ensemble. The wavelength of the light was converted to the telecom one at 1522 nm
by using a second-order nonlinearlity in a periodically-poled lithium niobate. By the HanburyBrown and Twiss experiment, we measured the autocorrelation function of the telecom light.
The observed value was clearly below 1, which shows the non-classical photon statistics of
the light after the wavelength conversion.
P2-187 Few-Photon Heterodyne Spectroscopy
Gustavo Amaral, Thiago Ferreira Da Silva, Guilherme Temporão and Jean Pierre von der
Weid
Abstract: We perform a high resolution Fourier Transform Spectroscopy of optical sources in
the few-photon regime based on the phenomenon of two-photon interference in a beam
splitter. From the heterodyne interferogram between test and reference sources it is possible
to obtain the spectrum of the test source relative to that of the reference. The method proves
to be a useful asset for spectral characterization of faint optical sources below the range
covered by classical heterodyne beating techniques.
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P2-188 Controlling two-photon frequency entanglement using cross-Kerr effect
Nobuyuki Matsuda
Abstract: The frequency conversion of quantum light is a crucial technology for quantum
networking. We have recently developed a scheme for realizing spectral and temporal
reshaping of single photon wave packets using cross phase modulation (XPM). Here we
demonstrate that quantum entanglement of correlated photons remains throughout XPM
using a two-photon interference experiment.
P2-189 Experimental detection of entanglement with optimal-witness families
Jibo Dai, Yink Loong Len, Yong Siah Teo, Berthold-Georg Englert and Leonid A. Krivitsky
Abstract: We report an experiment in which one determines, with least tomographic effort,
whether an unknown two-photon polarization state is entangled or separable. The method
measures whole families of optimal entanglement witnesses. We introduce adaptive
measurement schemes that greatly speed up the entanglement detection. The experiments
are performed on states of different ranks, and we find good agreement with results from
computer simulations.
P2-190 Irreversibility and the Arrow of Time in a Quenched Quantum System
Tiago Batalhao, Alexandre Souza, Roberto Sarthour, Ivan Oliveira, Mauro Paternostro, Eric
Lutz and Roberto Serra.
Abstract: Irreversibility is one of the most intriguing concepts in physics. While microscopic
physical laws are perfectly reversible, macroscopic average behavior has a preferred
direction of time. According to the second law of thermodynamics, this arrow of time is
associated with a positive mean entropy production. Using a nuclear magnetic resonance
setup, we measure the nonequilibrium entropy produced in an isolated spin-1/2 system
following fast quenches of an external magnetic field. We experimentally demonstrate that it
is equal to the entropic distance, expressed by the Kullback-Leibler divergence, between a
microscopic process and its time reversal. Our result addresses the concept of irreversibility
from a microscopic quantum standpoint.
Paper is available at http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.115.190601, and
comments are available at http://physics.aps.org/articles/v8/106
P2-191 Simple and Efficient Memory-Assisted Quantum Key Distribution
Nicolo Lo Piparo, Mohsen Razavi and William Munro
Abstract: Memory-assisted quantum key distribution (MA-QKD) aims to use current
quantum-device technologies to offer better rate-versus-distance behavior than that of
conventional QKD systems. Here, we present a novel system that relies on only one
physical memory: a nitrogen-vacancy (NV) center embedded into a cavity. We calculate the
secret key rate of such a system by considering all major sources of error and we show that,
in certain regimes of operation, our system leads to a key rate enhancement compared to
the no-memory QKD systems for distances larger than 200 km.
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P2-193 An explicit classical strategy for winning a CHSH_q game
Matej Pivoluska and Martin Plesch
Abstract: A CHSH_q game is a generalization of the standard two player CHSH game,
having q different input and output options. In contrast to the binary game, the best classical
and quantum winning strategies are not known exactly. In our work we provide a
constructive classical strategy for winning a CHSH_q game, with q being a prime. Our
construction achieves a winning probability better than 1/22*q^(-2/3), which is in contrast
with the previously known constructive strategies achieving only the winning probability of
O(q^-1).
P2-194 Isotropy and control of dissipative quantum dynamics
Ben Dive, Daniel Burgarth and Florian Mintert
Abstract: We investigate the problem of what evolutions an open quantum system with
Hamiltonian controls can undergo. A series of no-go theorems, primarily based on the
anisotropy of spectral properties, are given which exclude channels from being reachable for
any unitary controls. As well as studying examples of the use and strength of these criteria,
we explore their relation with existing approaches on the controllability of open quantum
systems and links with quantum thermodynamics.
P2-195 Quantum Theory of Two-Dimensional Resolution for Two Incoherent Optical
Point Sources
Shan Zheng Ang, Ranjith Nair and Mankei Tsang
Abstract: We obtain the quantum Cramer-Rao (QCR) bound for estimating the 2-D
separation of two incoherent optical point sources. The bound is independent of the x- and yseparations. We also propose a linear-optics-based measurement scheme that attains the
quantum bound for sub-Rayleigh separations.
P2-197 Unified view of quantum
transformation
Mengjun Hu and Yongsheng Zhang
amplification
based
on
quantum
states
Abstract: A general framework of quantum state amplification using the language of quantum
state transformation is given systematically. The concept of amplification of quantum states
is defined specifically and the amplification of a set of quantum states is formulated generally
as the transformation of quantum states. Three different kinds of important quantum
amplifications, i.e., deterministic noisy quantum amplification, probabilistic noiseless
quantum amplification, and deterministic noiseless quantum amplification are identified and
discussed. For deterministic quantum amplification, the linearity of amplification is proven to
be incompatible with the noiseless amplification while it is not true for probabilistic quantum
amplification. However, deterministic noiseless quantum amplification is shown physically
attainable if the requirement of linearity of amplification is relaxed. The relation between the
gain of amplification and the success probability is discussed for probabilistic quantum
amplification. Assuming that success probability is the same for all quantum states to be
amplified, we obtain a generally valid relation between the gain of amplification and the
success probability. Particular interest is given to phase-preserving quantum amplification of
Gaussian states which has been shown of theoretical interest and of practical importance in
quantum information and quantum communication recently. Our results of quantum state
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amplification not only enrich the research of quantum amplification but also can be helpful for
further practical applications.
P2-198 Two-atom interferences in a cavity QED system
Olivier Morin, Andreas Neuzner, Matthias Körber, Stephan Ritter and Gerhard Rempe
Abstract: A single-atom in a cavity is the most simple system of cavity quantum
electrodynamics and constitutes a tremendous platform for quantum information. Increasing
the system up to two atoms offers new possibilities in terms of amount of information that
one can process, presents new physical effects and remains highly non-linear, in contrast to
large atomic ensembles. Here, we show the experimental study of such a system by
trapping two atoms in a high-finesse cavity combined with a single-site-resolved imaging
technique. As for the paradigmatic double-slit experiment, we observe the fundamental role
of the relative phase between possible optical paths determined by the atoms' relative
positions. Indeed, this new degree of freedom introduces non-trivial effects based on the
cavity-mediated long-range interaction between the atoms. Furthermore, those results
witness the high level of control achieved in our experimental setup and its suitability for twoatom based quantum information protocols.
P2-199 Exploring the limits of non-locality with pairs of photons
Alessandro Cere, Hou Shun Poh, Siddarth Koduru Joshi, Adán Cabello, Marcin Markiewicz,
Pawel Kurzynski, Dagomir Kaszlikowski and Christian Kurtsiefer.
Abstract: Bell inequalities are a powerful tool in discriminating whether Nature is better
described by classical theories or non-local ones. I will present our efforts in experimentally
test Bell inequalities and the predictions of standard quantum mechanics using a source of
polarization entangled photon pairs, in particular our most recent two works. In the first, we
attempt to saturate the Tsirelson bound, the well known 2sqrt(2) predicted by standard
quantum mechanics. This attempt allowed us to exclude some of the alternative, non-local
theories [1]. In the second, I present an approach to discriminate between classical and nonclassical system based on the computational complexity of the output, as opposed to the
statistical nature of the standard Bell tests [2].
[1] Poh, H. S., et al., "Approaching Tsirelson's bound in a photon pair experiment," PRL 115,
180408 (2015)
[2] Poh, H. S., et al., "Probing quantum-classical boundary with compression software,"
http://arxiv.org/abs/1504.03126 (2015)
P2-200 Control and characterisation of nuclear spin memory in diamond nanocrystals
Jan D. Beitner, Helena S. Knowles, Dhiren M. Kara, David-Dominik H. Jarausch and Mete
Atatüre
Abstract: Nitrogen-vacancy (NV) centres in diamond are excellent sensors for magnetic and
electric fields, and temperature. Embedded in nanodiamonds they allow in vivo sensing.
However, measurements are restricted by the short electron spin coherence time typically
seen in nanocrystals. Sensitivity can be increased by taking advantage of the NV host
nuclear nitrogen spin. Here, we demonstrate initialisation of the nuclear spin and, measure a
lifetime exceeding 15 milliseconds and a coherence time of 241 microseconds, limited by the
lifetime of the NV electron spin. This result enhances the potential sensitivities and spectral
resolution of nano-MRI measurements achievable with such NV centres.
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P2-201 Long coherence time quantum memory for polarization qubits based on a
single atom in a cavity
Olivier Morin, Matthias Körber, Stefan Langenfeld, Andreas Neuzner, Stephan Ritter and
Gerhard Rempe
Abstract: Extended storage of quantum information is a long standing goal since decades. It
is particularly motivated by the fact that quantum network implementations strongly rely on
quantum memories for light. Long storage time and high efficiency are the main two figures
of merit for a quantum memory. However, it remains challenging to fulfill both criteria at a
level that is sufficient to beat classical systems. The use of single atoms as a light-matter
interface offers the advantage of reducing the number of external and internal degrees of
freedom. This is particularly relevant for the realization of quantum information tasks where
decoherence mechanisms mostly come from a lack of control on the system. Here, we
present a single-atom-based quantum memory with a read-write efficiency of about 10\%
and a storage time on the order of 10ms. Mainly, decoherence induced by magnetic field
fluctuations is overcome by coherent manipulation of the atomic state after writing the qubit,
to move the information into a pseudo-clock state that is less sensitive to magnetic field
fluctuations. This paves the way for the implementation of long distance quantum
communication protocols e.g. quantum repeaters.
P2-202 Quantum approaches to homomorphic encryption
Joshua Kettlewell, Carlos Perez-Delgado, Yingkai Ouyang, Si-Hui Tan, Li Yu, Lin Chen and
Joseph Fitzsimons
Abstract: The advent of computationally secure fully homomorphic encryption schemes has
had a dramatic impact on the field of cryptography. Such encryption schemes allow for
information processing to be performed on encrypted data without decryption and in a purely
non-interactive way. By necessity, however, classical approaches are limited to security only
under certain assumptions about the computational power of the adversary.
Here we explore the question of whether a quantum approach might offer stronger security
guarantees. We prove both a no-go theorem, showing that fully homomorphic encryption is
impossible if the mutual information between ciphertext and plaintext is required to be
exactly zero. When this restriction on the mutual information is relaxed, however, non-trivial
privacy homomorphisms become possible. We introduce two explicit protocols which admit
non-trivial computational models, models which cannot be simulated classically, while still
placing strong limits on the information content of cipher texts.
Based on arXiv:1406.2456, arXiv:1411.5254 and arXiv:1508.00938
P2-204 Silicon-vacancy: a colourful defect of diamond as solid-state single-spin for
quantum information.
Camille Stavrakas, Benjamin Pingault, Christian Hepp, Tina Müller, Mustafa Gündogan,
Jonas Becker, Carsten Schulte, Carsten Arend, Tillman Godde, Alexander Tartakovskii,
Matthew Markham, Christoph Becher, Elke Neu, Stefan Gsell, Matthias Schreck, Hadwig S
Abstract: While pure diamond transmits visible light and appears as a clear colourless
crystal, the implantation of defects such as impurities or vacancies in the diamond lattice
during or after the gemstone's formation can lead to changes in its electronic band structure
97
and therefore a change in colour - this is how boron made the famous Hope Diamond so
remarkably blue. The local electronic perturbation caused by such defects, called 'colourcentres', creates discrete electronic states within the insulator's bandgap similar to those of
an atom, whose spin states can be addressed individually and manipulated with light. We
study a silicon-based colour-centre, the negatively charged silicon-vacancy (SiV-). Within the
crystal lattice, an implanted silicon atom does not exactly sit in place of the carbon atom that
it replaced. Instead, there is a split-vacancy configuration between the unoccupied lattice
sites and the nearest neighbour carbon atoms [1]. It differs from the more abundant and
extensively-studied nitrogen-vacancy (NV-) in that 80 percent of its emission [2] (where it is 4
percent for NV-) is in a narrow zero-phonon-line (ZPL) at 737 nm at cryogenic temperatures
[3]. Our experimental and theoretical work, particularly over the last three years, has
unravelled the electronic structure of 28Si SiV centres [1,3]. This contributed to a profound
understanding of its internal level structure which made optically accessible the electronic
spin of these defects. Due to the split vacancy, the extra electron of the SiV centre sees a
double-well potential, giving it two possible orbital configurations with the same energy.
Besides, the electron possesses intrinsically another degree of freedom: its spin state which
can be up or down. Since there are four possible arrangements (combinations) of orbital and
spin degrees of freedom (spin up and spin down for each of the two orbitals), both the
ground and excited states are four-fold degenerate. Spin-orbit coupling lifts the orbital
degeneracy and therefore the total degeneracy becomes a two-fold (spin only). By exposing
single SiVs to a magnetic field where the Zeeman effect lifts the remaining spin degeneracy,
we were able to test our model successfully and show that SiVs possess a spin one-half
[1,3]. Using resonant laser excitation at cryogenic temperatures, we were able to report spintagged resonance fluorescence and reveal a spin-state purity approaching unity in the
excited state, highlighting the potential of the centre as an efficient spin-photon quantum
interface. Preparing coherent superposition states of the electronic spin that could be used
as quantum bits enabled us to achieve coherent population trapping (CPT) and measure a
spin coherence time of the ground state [5] over 45 ns. Our efforts are now directed towards
the realisation of the all-optical control of the electronic spin and the identification of the main
sources of spin decoherence. The combination of ultrafast coherent control of individual
spins and the high quality and reproducibility of the optical spectrum across multiple SiVcenters can serve to realise the basic components of a distributed quantum network.
[1] Muller, T et al. Optical signatures of silicon-vacancy spins in diamond. Nature
communications, 5, 3328, 2014.
[2] Aharonovich, I et al. Diamond photonics. Nature Photonics, 5, 397–405, 2011.
[3] Feng, T et al. Characteristics and origin of the 1.681 eV luminescence center in chemicalvapor-deposited diamond films. Journal of Applied Physics, 73, 1415, 1993.
[4] Hepp, C et al. Electronic Structure of the Silicon Vacancy Color Center in Diamond.
Physical Review Letters, 112, 036405, 2014.
[5] Pingault, B, Becker, J et al. All-Optical Formation of Coherent Dark States of SiliconVacancy Spins in Diamond. Physical Review Letters, 113, 263601, 2014.
P2-205 Photon Antibunching and Hong-Ou-Mandel Peak
Gustavo Amaral, Felipe Calliari, Thiago Ferreira Da Silva, Guilherme Temporão and Jean
Pierre von der Weid
Abstract: Photon antibunching was observed in a modified Hong-Ou-Mandel interferometer
as a peak in the coincidence count events between detectors. The inversion of the
interference pattern is equally observed when the wave packets are frequency displaced.
The mathematical description agrees with the experimental results when the correction for
weak coherent states in included. The second order autocorrelation function at zero time
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was experimentally determined by means of the Hanburry-Brown and Twiss experiment
when a photon at one arm of the interferometer's output heralds the presence of the other.
P2-207 Quantum assisted Gaussian process regression
Zhikuan Zhao, Jack Fitzsimons and Joseph Fitzsimons
Abstract: Gaussian Process Regression is widely considered as a powerful model for
regression problems in the field of supervised machine learning. However its practicality is
limited by the slow runtime on a classical computer when applying to problems involving
inference from large sets of data. In this work, we present a novel application of an extended
version of the quantum algorithm for linear systems [Harrow et al., Phys. Rev. Lett. 103,
150502 (2009)] to speedup the computation of Gaussian Processes. A preprint of this work
appears as arXiv:1512.03929.
P2-208 Entanglement conditions for integrated-optics multi-port
interferometry experiments
Junghee Ryu, Marcin Marciniak, Marcin Wiesniak and Marek Zukowski
quantum
Abstract: Integrated optics allows one to perform interferometric experiments based upon
multi-port beam-splitter. To observe entanglement effects one can use multi-mode
parametric down-conversion emissions. When the structure of the Hamiltonian governing the
emissions has (infinitely) many equivalent Schmidt decompositions into modes (beams), one
can have perfect EPR-like correlations of numbers of photons emitted into “conjugate
modes” which can be monitored at spatially separated detection stations. We provide series
of entanglement conditions for all prime numbers of modes, and show their violations by
bright multi-mode squeezed vacuum states. One family of such conditions is given in terms
of the usual intensity-related variables. Moreover, we show that an alternative series of
conditions expressed in terms averages of observed rates, which is a generalization of the
ones given in arXiv:1508.02368, is a much better entanglement indicator. Thus the rates
seem to emerge as a powerful concept in quantum optics.
P2-209 Fault-tolerant Quantum Computation under non-Markovian noise
Jing Hao Chai and Hui Khoon Ng
Abstract: In the control of quantum systems, noise is a major hurdle to overcome. For a
sequence of operations on an input quantum state, noise causes the output quantum state
to deviate from the ideal situation. Encoding the qubit as multi-qubit physical systems,
applying error correction and using fault-tolerant design for quantum operations are some of
the methods that can be used to protect quantum information from noise. However, these
schemes increase the complexity of the system, which increases the error rate of the
system. The error rate of such systems under these schemes for a given noise model gives
us a gauge of the usefulness of these schemes. However the complexity of the overall
schemes makes it difficult to calculate this number. A certain class of such systems and
operations is simulable numerically in an efficient manner, via the stabilizer formalism and
Gottesman-Knill theorem. In such schemes, it is usually assumed for analysis that errors are
non-correlated between physical qubits and different times. Moreover, a noise map is usually
derived from a master equation of Lindblad form, or equivalently taken as a completely
positive, trace-preserving map. Such a treatment for noise assumes that the environment
contains no memory or that the memory time is much shorter that the timescale of intended
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quantum operations. Though such an assumption is usually reasonable, the concept of fault
tolerance involves the question of whether such schemes are robust to different types of
noise. Prior study have shown a wide disparity between the feasibility of such schemes
under non-Markovian noise than compared to Markovian ones. To investigate if this were
really the case, we propose to consider a situation where controlled quantum systems
possess small but uncontrollable quantum degrees of freedom, which we call the “small
bath”. The small bath is capable of holding a limited amount of memory of past interactions
with the system. We are therefore interested in the effect of such a small bath has on the
error rates of the system, and how this changes when the dimension of the small bath
changes. Using the stabilizer formalism, we are able to capture some simple dynamics of the
non-Markovian noise with a toy model of a system that has applied operations and error
correction cycles. A direct simulation of the dynamics of this kind of system therefore allow
for observation of patterns and provide estimations of error rates which would otherwise be
too complicated to solve analytically. In order to verify that the simulation functions as
intended, we first used it to verify the threshold derived by others for different schemes. In so
doing, we were able to locate the assumptions used to derive the threshold, and identify their
impact on the threshold. It is ultimately hoped that the numerical results provided by this toy
model of non-Markovian noise can aid more rigorous analyses for such noise in quantum
systems.
P2-210 Quantum Phase Transition and Universal Dynamics in the Rabi Model
Myung-Joong Hwang, Ricardo Puebla and Martin B. Plenio
Abstract: We show that the Rabi model undergoes a second-order superradiant quantum
phase transition [1]. Given that the Rabi model consists only of a single atom and a singlemode cavity field, this finding is surprising, as it is commonly assumed that a quantum phase
transition occurs in infinitely extended systems, in terms of a number of system components.
We prove the QPT by deriving an exact solution in the limit where the atomic transition
frequency in unit of the cavity frequency tends to infinity. The effect of a finite transition
frequency is studied by analytically calculating finite-frequency scaling exponents as well as
performing a numerically exact diagonalization. Going beyond this equilibrium QPT setting,
we prove that the dynamics under slow quenches in the vicinity of the critical point is
universal, that is, the dynamics is completely characterized by critical exponents. Our
analysis demonstrates that the Kibble-Zurek mechanism can precisely predict the universal
scaling of residual energy for a model without spatial degrees of freedom. Moreover, we find
that the onset of the universal dynamics can be observed even with a finite transition
frequency. References: [1] M.-J. Hwang, R. Puebla, and M. B. Plenio, Physical Review
Letters 115, 180404 (2015); selected as Editors' suggestion.
P2-212 Prospects for Atomic Spin-Squeezing inside Hollow-Core Photonic Crystal
Fiber
Zilong Chen and Shau-Yu Lan
Abstract: Hollow-core photonic crystal fibers have matured to a point where laser-cooled
atomic ensembles have been loaded into these fibers, forming a high optical density medium
naturally suited for nonlinear optics applications. Increasingly, researchers are utilizing the
same platform for quantum metrology applications, for example as optical lattice clock, or as
atom interferometer in our group at NTU, Singapore, with advantages in compactness and
potentially better control over systematics over conventional atomic sensors. However, the
typically small ensemble size, N, implies the precision of the sensor is limited by the
standard quantum limit to the poor absolute precision of 1/sqrt(N) when using un-entangled
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atoms. The standard quantum limit can be overcome by using atomic spin-squeezed states,
which are entangled. Spin-squeezing is an extremely promising approach, with ~18-20dB
metrological improvement already demonstrated in cavity-based systems and ~3dB in free
space setups. In this presentation, I will explore the prospects of generating spin-squeezed
states on the clock states of Rb-87 atoms inside a hollow-core photonic crystal fiber setup
using quantum non-demolition measurements.
P2-215 Coherent manipulation of small ion Coulomb crystals in a Penning Trap
Pavel Hrmo, Manoj Joshi, Vincent Jarlaud, Joseph Goodwin, Graham Stutter and Richard
Thompson
Abstract: Trapped ions in a Penning trap provide a fruitful environment for quantum
simulation. We investigated the preparation of small, laser cooled Coulomb crystals for
potential for use in such simulations. Our previous work demonstrated the ground state
cooling of a single 40Ca+ ion using resolved sideband laser cooling. We extend this
technique to cooling two ions both in an axial chain and in the radial plane of the trap. We
cool the centre of mass modes for both configurations and the breathing and tilt modes for
the axial and planar crystal respectively. To check the coherence time of our qubits we
performed Ramsey spectroscopy and applied dynamical decoupling techniques to extend
this time by more than a factor of 5. Furthermore, we present our efforts to realise a two
qubit gate on the two ion crystal.
P2-219 Unifying wave-particle duality with entropic uncertainty
Patrick Coles, Jedrzej Kaniewski and Stephanie Wehner
Abstract: An interferometer - no matter how clever the design - cannot reveal both the wave
and particle behavior of a quantum system. This fundamental idea has been captured by
inequalities, so-called wave-particle duality relations (WPDRs), that upper bound the sum of
the fringe visibility (wave behavior) and path distinguishability (particle behavior). Another
fundamental idea is Heisenberg's uncertainty principle, stating that some pairs of
observables cannot be known simultaneously. The distinction between these two concepts
has been debated in the literature. Here we provide closure to the debate by showing that
WPDRs correspond to a modern formulation of the uncertainty principle, namely, the
uncertainty relation for the min- and max-entropies, which is used in quantum cryptography.
Furthermore, our unification provides a framework for solving an outstanding problem of how
to formulate universally valid WPDRs for interferometers with more than two paths, and we
employ this framework to derive some novel WPDRs.
P2-222 Generalised phase kick-back: the structure of computational algorithms from
physical principles
Ciaran Lee and John Selby
Abstract: The advent of quantum computing has challenged classical conceptions of which
problems are efficiently solvable in our physical world. This motivates the general study of
how physical principles bound computational power. In this paper we show that some of the
essential machinery of quantum computation – namely reversible controlled transformations
and the phase kick-back mechanism – exist in any operational-defined theory with a
consistent notion of information. These results provide the tools for an exploration of the
physics underpinning the structure of computational algorithms. We investigate the
relationship between interference behaviour and computational power, demonstrating that
101
non-trivial interference behaviour is a general resource for post-classical computation. In
proving the above, we connect higher-order interference to the existence of post-quantum
particle types, potentially providing a novel experimental test for higher-order interference.
Finally, we conjecture that theories with post-quantum interference – the higher-order
interference of Sorkin – can solve problems intractable even on a quantum computer.
P2-223 Generation of single photons with highly tunable wave shape from a cold
atomic quantum memory
Pau Farrera, Georg Heinze, Boris Albrecht, Melvyn Ho, Matías Chávez, Colin Teo, Nicolas
Sangouard and Hugues de Riedmatten
Abstract: We report on a single photon source with highly tunable photon shape based on
cold ensemble of Rubidium atoms. We follow the DLCZ scheme to implement an emissive
quantum memory, which can be operated as a photon pair source with controllable delay.
We find that the temporal wave shape of the emitted read photon can be precisely controlled
by changing the shape of the driving read pulse. We generate photons with temporal
durations varying over three orders of magnitude up to 10 μs without a significant change of
the read-out efficiency. We prove the non-classicality of the emitted photons by measuring
their antibunching, showing near single photon behavior at low excitation probabilities. We
also show that the photons are emitted in a pure state by measuring unconditional
autocorrelation functions. Finally, to demonstrate the usability of the source for realistic
applications, we create ultra-long single photons with a rising exponential or doubly peaked
wave shape which are important for several quantum information tasks.
P2-225 High Efficiency Room-Temperature Raman Memory using Quenching
Sarah Thomas, Patrick Ledingham, Benjamin Brecht, Joseph Munns, Cheng Qiu, Amir
Feizpour, Ian Walmsley, Joshua Nunn and Dylan Saunders
Abstract: Optical quantum information processing offers a very promising platform for
quantum technologies because photons are essentially noise-free at room temperature and
have many degrees of freedom in which information can be encoded. However, the
generation of deterministic single photons remains an unsolved problem. Quantum
memories could be used to synchronise probabilistic single photon sources and significantly
reduce the waiting time for many-photons states [1].
For temporal multiplexing it is critical to have both a high memory efficiency η and a large
time-bandwidth product B. This product, B=τδ, quantifies the maximum number of
multiplexing operations, determined by the memory bandwidth δ, within the storage lifetime
of the memory, τ. Warm broadband Raman memories are a strong candidate for temporalmultiplexing as time-bandwidth products of B~1000 have been demonstrated [2]. However,
to date broadband Raman memories have been limited in efficiency to η~30% [2]. Here we
improve the state-of-the-art for broadband Raman memories and improve the memory
efficiency to η=57±5%, without any adverse effects to the time-bandwidth product.
The Raman memory protocol uses a Λ-level scheme to adiabatically transfer population
between ground states via an off-resonant Raman transition. We implement the Raman
protocol using the D2 transition in caesium. The total memory efficiency η is proportional to
the square of the optical depth of the Cs vapour which increases exponentially with
temperature. However, above 70°C, our ability to prepare the memory in the initial state, via
optical pumping, with high fidelity decreases rapidly due to radiation trapping: photons
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emitted by spontaneous decay in the optical pumping process can depolarise other atoms if
the vapour is optically thick [3].
To fully polarise the ensemble at higher temperatures we reduce the effect of radiation
trapping by quenching: atoms collide with a molecular buffer gas and transfer their energy to
the vibrational modes of the molecule. By introducing 10 Torr of N2 as a buffer gas we
suppress radiation trapping and can polarise the Cs ensemble up to 90°C (Fig. 1(a)). This
allows us to operate the Raman memory at much higher optical depths, significantly
increasing the Raman coupling constant. We observe a memory efficiency of 57±5%; almost
double previous results (Fig. 1(b)). We expect the addition of quenching to warm alkali
quantum memories to play a significant role in next generation light-matter interactions at
room-temperature.
[1] Nunn, J. et al. "Enhancing multiphoton rates with quantum memories." Phys. Rev. Lett.
110, 133601 (2013).
[2] Michelberger, P. S. et al. "Interfacing GHz-bandwidth heralded single photons with a
warm vapour Raman memory." New Journal of Physics (2015).
[3] Molisch, A. F. & Oehry, B. P. "Radiation Trapping in Atomic Vapours" (Oxford Science
Publications, 1998).
P2-226 Inertial Navigation using Atom Interferometry
Jimmy Stammers, Xiaxi Cheng and Ed Hinds
Abstract: In recent years, atom interferometry has been used to measure inertial forces,
such as acceleration due to Earth's gravity, to remarkable precision. Developments into
robust and compact laser sources has also enabled atomic gravimeters to be operated
outside of typical laboratory environments. This raises the prospect of inertial navigation
using atom interferometry as an additional practical application. Conventional inertial
navigation systems employ extremely precise measurements of acceleration and rotation to
determine position over time, but are prone to bias drifts that limit their long-term accuracy.
This can be improved using the intrinsic stabilty of atoms to correct for measurement errors
of a mechanical accelerometer. In turn, the high bandwidth accelerometer signal eliminates
the problem of measurement dead time of the interferometer, associated with trapping and
cooling an atomic ensemble. We present work on the design and operation of a hybrid atom
interferometer and mechanical accelerometer system to measure a range of linear
acceleration.
P2-231 A Cavity-Enhanced Room-Temperature Broadband Quantum Memory for
Nanosecond Heralded Single Photons
Dylan Saunders, J. H. D. Munns, T. F. M. Champion, C. Qiu, S. E. Thomas, B. Brecht, K. T.
Kaczmarek, E. Poem, P. M. Ledingham, I. A. Walmsley and J. Nunn
Abstract: Broadband quantum memories hold great promise as multiplexing elements in
future photonic quantum information protocols. Alkali vapour Raman memories combine
high-bandwidth storage, on-demand read-out, and operation at room temperature without
collisional fluorescence noise. However, previous implementations have required large
control pulse energies and suffered from four-wave mixing noise. Here we present a Raman
memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned
into simultaneous resonance with the signal and control fields, dramatically reducing the
energy required to drive the memory. By engineering anti-resonance for the anti-Stokes field,
103
we also suppress the four-wave mixing noise and report the lowest unconditional noise floor
yet achieved in a Raman-type warm vapour memory, $(15\pm2)\times10^{-3}$ photons per
pulse, with a total efficiency of $(9.5\pm0.5)$\%.
P2-232 Quantum parameter estimation with general dynamics
Haidong Yuan and Chi-Hang Fung
Abstract: One of the main quests in quantum metrology, and quantum parameter estimation
in general, is to find out the highest achievable precision with given resources and design
schemes to attain it. In this article we present a general framework for quantum parameter
estimation which relates the ultimate precision limit directly to the geometrical properties of
underlying dynamics. With this framework we present systematic methods for computing the
ultimate precision limit and optimal probe states. We further demonstrate the power of the
framework by deriving a sufficient condition on when ancillary systems are not useful for
improving the precision limit.
P2-233 Modelling Atom-Filled Optical Cavities for Enhanced Light-Matter Interaction
Joseph Munns, Sarah E. Thomas, Benjamin Brecht, Patrick M. Ledingham, Ian A. Walmsley,
Joshua Nunn and Dylan J. Saunders
Abstract: A means for precise experimental characterization of the dielectric susceptibility of
an atomic ensemble inside an optical cavity is important for design and operation of quantum
light matter interfaces, particularly in the context of quantum information processing. Here
we present a numerically optimised theoretical model to predict the spectral response of an
atom-filled cavity, including both homogeneous and inhomogeneous broadening at high
optical densities. We investigate the regime where the two broadening mechanisms are of
similar magnitude, which makes the use of common approximations invalid. Our model
agrees with an experimental implementation with warm caesium vapour in a ring cavity.
P2-234 The Quantum-Classical Boundary for Precision Interferometric Measurements
Patrick M. Birchall, Jeremy L. O'Brien, Jonathan C. F. Matthews and Hugo Cable
Abstract: Precise measurements of optical phase underlie many technological and scientific
investigative techniques, therefore understanding how to maximize the precision of these
measurements is of key interest. We consider the task of measuring an optical phase, which
has an associated loss, whilst minimizing the number of photons incident upon the phase. It
is often argued that an important quantum advantage can be obtained for this task in the
measurement of delicate or photosensitive samples. We study the achievable precision one
can obtain whilst utilizing only classical techniques and compare these strategies to
fundamental limitations on the attainable precision imposed by quantum mechanics found in
previous studies. We devise an optical setup which is able to measure a phase with a rootmean-square error of only ~4% larger than an optimal non-classical strategy. We also
present provide potentially practical strategies using either classical or non-classical
techniques which provide a precision close to the optimal non-classical strategy. These
results are presented in arXiv:1602.07561.
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P2-235 Entanglement is an inevitable feature of a non-classical universe
Jonathan Richens, John Selby and Sabri Al-Safi
Abstract: One of the most striking features of quantum theory is the existence of entangled
states, responsible for Einstein's so called ``spooky action at a distance''. These states
emerge as part of the mathematical formalism of quantum theory, but to date there exists no
set of simple physical axioms that predict their existence. For example, existing
reconstructions of quantum theory in the framework of generalised probabilistic theories can
be see as derivations of entanglement from physical or informational principles, but can
hardly be viewed as a minimal set of physical properties from which the existence of
entangled states can be derived. In the presented work I will show that all physical theories
that can be represented as generalised probabilistic theories must have dynamics that
generate entangled states, making only the very minimal assumption of reversible
transitivity.
Reversible transitivity is a feature shared by both quantum and classical theory. I states that
the state space of a closed system is preserved and can be fully explored by the dynamics
permitted by the theory. Reversibility is an essential property of quantum theory as it ensures
that information cannot be destroyed or cloned, and is thus believed to be an essential
feature of any likely / reasonable theory of nature. For example, without reversibility the
second law of thermodynamics could be routinely and systematically broken. Transitivity is
the requirement that all states in the state space can be reached under the allowed
dynamics from all others. With reversibility, this can be absorbed into the definition of a state
space - i.e. the set of all states that can be generated.
We consider all reversibly transitive interacting theories and find that all, with the exception
of classical probability theory, must have dynamics that generate entangled states. By
relaxing the postulate of transitivity we find that reversibility and information gain implies
disturbance are sufficient to imply the existence of entangled states. These postulates derive
the phenomenon of entanglement from purely physical principles, and establish
entanglement as an inevitable feature of any natural non-classical probabilistic theory of
nature.
The ramifications of these results are surprising. For example, one could in principle (without
any knowledge of quantum theory) observe any non-classical phenomena (such as
interference) and imply that existence of entangled states.
P2-237 The Quantum Simulation of Quantum Chemistry
Andrew Tranter, Peter Coveney, Florian Mintert and Peter Love
Abstract: Fundamental to quantum chemistry is the determination of ground state energies
of molecular systems. It is known that a quantum device would allow for an exponential
speedup of the exact calculation of such energies, allowing for more accurate computational
analysis of chemical reactions. In this poster, we aim to give a broad overview as to some of
the techniques involved in implementing electronic structure calculations on a quantum
device. In particular we consider the Bravyi-Kitaev mapping - an alternative to the traditional
Jordan-Wigner mapping of electronic operators to qubit operators. We also consider the
impact of ordering schemes in a Trotterized Hamiltonian. Finally, we discuss the
consequences of these techniques with regards to quantum resource requirements, and the
implications of this for near-future experimental work demonstrating these techniques.
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P2-240 Optimal Wavelength Assignment in Hybrid Quantum-Classical DWDM
Networks
Sima Bahrani, Mohsen Razavi and Jawad A. Salehi
Abstract: An efficient algorithm for optimal allocation of wavelengths in a hybrid densewavelength-division-multiplexing (DWDM) system, carrying both quantum and classical data,
is proposed. The transmission of quantum bits alongside intense classical signals on the
same fiber faces major challenges arising from the background noise generated by classical
channels. Raman scattering, in particular, is shown to have detrimental effects on the
performance of quantum key distribution systems. Here, by using an optimal wavelength
allocation technique, we minimize the Raman induced background noise on quantum
channels, hence maximize the achievable secret key generation rate for quantum channels.
We show that the conventional solution that involves splitting the spectrum into only two
bands, one for quantum and one for classical channels, is not necessarily optimum, and, in
fact, could generate a key rate considerably lower then that of the optimal assignment. We
show that, in the latter optimal case, we might need several quantum and classical bands
interspersed among each other.
P2-241 General method for constructing local-hidden-state (and -variable) models for
multiqubit entangled states
Rafael Rabelo, Daniel Cavalcanti, Leonardo Guerini and Paul Skrzypczyk
Abstract: We propose a numerical method for constructing local-hidden-state (LHS) models
– and consequently local-hidden-variable (LHV) models – for multiqubit states based on
semidefinite programming. This method can be applied to arbitrary states and general
(POVM) measurements and can also be adapted to generate random states with LHS
models. As applications we present new families of states with LHS models, including Belldiagonal states, noisy GHZ and noisy W states, and generate a list of over 400000 new
entangled two-qubit states with LHS model for projective measurements and 1400 for POVM
measurements.
P2-242 Towards Long Range Spin-Spin Interactions via Mechanical Resonators
Arthur Safira, Jan Gieseler, Aaron Kabcenell, Shimon Kolkowitz, Alexander Zibrov, Jack
Harris and Mikhail Lukin
Abstract: Nitrogen vacancy centers (NVs) are promising candidates for quantum
computation, with room temperature optical spin read-out and initialization, microwave
manipulability, and weak coupling to the environment resulting in long spin coherence times.
The major outstanding challenge involves engineering coherent interactions between the
spin states of spatially separated NV centers. To address this challenge, we are working
towards the experimental realization of mechanical spin transducers. We have successfully
fabricated magnetized high quality factor (Q>105), doubly-clamped silicon nitride mechanical
resonators integrated close to a diamond surface, and report on experimental progress
towards achieving the coherent coupling of the motion of these resonators with the electronic
spin states of individual NV centers under cryogenic conditions. Such a system is expected
to provide a scalable platform for mediating effective interactions between isolated spin
qubits.
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P2-245 Cold atom memory as a platform for quantum information
Geoff Campbell, Young-Wook Cho, Jian Su, Jesse Everett, Nicholas Robins, Ping Koy Lam
and Ben Buchler
Abstract: Numerous physical implementations of optical quantum memories exist, or have
been proposed, each offering its own merits and drawbacks. Here, we present the technical
details and characterisation of an implementation that is based on a collection of cold
rubidium 87 atoms. The atoms are trapped and cooled in an elongated magneto optical trap
(MOT) that provides an optical depth of approximately 600 on the F = 1 to F'=2 transition.
The coherence time of the hyperfine ground state transition is 1 ms, limited by the atomic
temperature of 100 micro-kelvin. The atomic population is optically pumped into a single
Zeeman sub-level to increase the optical depth and eliminate unwanted transitions. We
characterise the ensemble using imaging techniques and by analysing the performance as a
quantum memory. The racetrack-shaped magnetic fields coils provide open optical access
for absorption imaging of the cloud. The technique also allows us to directly monitor the
propagation of slow or stored light in the atoms. This provides direct feedback to optimally
align a probe field to the spatial profile of the atoms. We use both the electromagnetically
induced transparency (EIT) and Gradient Echo Memory (GEM) techniques to examine the
quantum performance of the MOT as a memory. EIT is used to demonstrate that the
dynamics of the light-atom interaction and unwanted four-wave-mixing (4WM) processes can
be effectively modelled and controlled. Using optical pumping, the 4WM process can be
eliminated. We use GEM to demonstrate that the memory adds little excess noise and
reproduces input states with a high fidelity (0.997 for a single-photon level coherent state).
The memory is shown to out-perform an ideal fibre loop and operates in the no-cloning
regime. We illustrate the flexibility of the cold-atom platform by presenting extensions to the
basic memory. We demonstrate temporally multi-mode storage for 20 pulses, all with an
efficiency of over 5%, and a frequency-domain dual-rail memory with an efficiency of 35%.
We also discuss using the cold-atom memory to implement arbitrary linear operations on
optical modes and how it may be used as an effective high-finesse optical resonator.
P2-246 Differential phase-time shifting protocol for QKD (DPTS)
Mario A. Usuga, Davide Bacco, Jesper Bjerge Christensen, Karsten Rottwitt, Leif K.
Oxenløwe and Yunhong Ding
Abstract: We explore the implementation of a novel protocol for fiber-based high-dimensional
quantum key distribution (QKD) which improves over the traditional DPS-QKD and COW
protocols.
P2-249 Where does measurement uncertainty come from?
Filip Rozpedek, Jedrzej Kaniewski, Patrick J. Coles and Stephanie Wehner
Abstract: Quantum correlations and measurement uncertainty are inherently linked. In this
context we are interested in the question whether measurement uncertainty is an inherent
property of the measured quantum system or whether it is a consequence of the lack of
knowledge about the measurement process. Specifically, let us consider the perspective of
entropic uncertainty relations, so that we are interested in the ability of some observer to
predict the measurement outcome. Then, assuming that the guessing party has access to
the quantum correlations between the measurement apparatus and the system measured, is
it possible for him to better predict the measurement outcome than in the classical scenario
where those correlations are inaccessible to the observer? To answer these questions we
use the model of the simple uncertainty games in which one performs one out of two
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incompatible measurements chosen uniformly at random and the uncertainty of the outcome
conditional on the basis choice is evaluated. In such games there will always be some
uncertainty of the measurement outcome independently of the input state. Since the basis
choice is probabilistic, it can be represented by a fully mixed register of dimension two. Here
we consider a more complex scenario, where the "basis" register is in a coherent
superposition state. We find that introducing coherence facilitates guessing and hence we
show that it leads to a qualitatively new class of problems.
P2-250 Fisher Information and Quantum Communication with random unitary noise
Wiesław Laskowski, Marcin Markiewicz and Anna de Rosier
Abstract: The effect of the collective random unitary noise on an input state, described by the
fidelity of the final state to the initial one, is difficult to assess, since it demands optimization
over O(d^2) parameters of a unitary transformation. We utilize the relation between Bures
fidelity and Quantum Fisher Information (QFI) in order to provide analytically tractable bound
on fidelity of a multipartite quantum state undergoing such collective unitary noise. This new
property of QFI enabling one to certify robustness against noise for different classes of
states. In order to get deeper insight into the problem of collective unitary noise we checked
statistical properties of fidelity by means of Monte Carlo simulations.
P2-252 Numerical simulation of topological codes using tensor networks
Andrew Darmawan and David Poulin
Abstract: The surface code is a promising candidate for quantum error correction in many
architectures, requiring only nearest-neighbour interactions on a two-dimensional square
lattice. Our understanding of the performance of the surface code is mostly based on
numerical simulations which have found a high threshold relative to other error correction
schemes. These simulations usually assume Pauli noise, which has the advantage that it
allows efficient simulation within the stabilizer formalism. However most realistic noise
processes (e.g. amplitude damping and systematic over rotation), are non-Pauli. In this work
we present an improved simulation scheme for the surface code under local non-Pauli noise.
Our schemes are based on the tensor network description of the surface code as a projected
entangled pair state (PEPS). Syndrome sampling, computation of the process matrix and
logical error rates can all be performed by contracting an appropriate tensor network.
P2-253 Distributing entangled states using silicon photonic chips
Jianwei Wang, Damien Bonneau, Matteo Villa, Joshua Silverstone, Raffaele Santagati,
Shigehito Miki, Taro Yamashita, Mikio Fujiwara, Masahide Sasaki, Hirotaka Terai, Michael
Tanner, Chandra Natarajan, Robert Hadfield, Jeremy O'Brien and Mark Thompson
Abstract: We demonstrate high-fidelity distribution of entanglement across two integrated
silicon photonic chips. Path-entangled Bell states are generated and manipulated on chip,
and coherently distributed between the two separate chips using a path-polarization
interconversion on each chip. The two-qubit states are analyzed on chips using
reconfigurable quantum circuits, and we observe a violation of the Bell-type inequality of
2.638±0.039, confirming the distribution of entanglement
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P2-256 Floodlight Quantum Key Distribution
Zheshen Zhang, Quntao Zhuang, Justin Dove, Franco Wong and Jeffrey Shapiro
Abstract: We introduce floodlight quantum key distribution (FL-QKD), which exploits multimode encoding to greatly boost secret-key efficiency (SKE) and secret-key rate (SKR). With
a coincidence-based channel-monitoring unit, FL-QKD is secure against collective attacks.
In our proof-of-principle experiment, we achieve 0.55 bits/channel-use SKE and 55 Mb/s
SKR over a channel with 10-dB propagation loss. The demonstrated SKE and SKR
represent more than 100-fold and 50-fold improvements, respectively, over state-of-the-art
QKD systems for the same channel attenuation.
P2-258 Symmetric Extendability of Quantum States and the Extreme Limits of
Quantum Key Distribution
Sumeet Khatri and Norbert Lutkenhaus
Abstract: We investigate QKD protocols with two-way communication that are based on the
quantum phase of the well-known BB84 and six-state protocols. The quantum phase
consists of the source sending quantum signals to the receiver, who measures them, leaving
only classical data on both sides. Our goal is to find the highest value of the quantum bit
error rate Q for which two-way classical post-processing protocols on the data can create
1
secret keys. Using the BB84 quantum phase, such protocols currently exist for Q ≤ . On
5
1
the other hand, for Q ≥ no such protocol can exist as the observed data is compatible with
4
an intercept-resend channel. This leaves the interesting question of whether successful
1
1
≤ Q ≤ . For the six-state protocol, the corresponding gap is
protocols exist in the gap
known to be
5− √5
≤
10
Q≤
1
.
3
5
4
The current lower bounds have previously been shown to come from the symmetric
extendability of the underlying quantum state shared between Alice and Bob after a two-way
protocol called advantage distillation. Our work looks more generally at two-way postprocessing protocols within the gap and asks the question of symmetric extendability of the
states after them, for if they are symmetrically extendable then no secret key is possible. We
have analyticallyconstructed a symmetric extension throughout the gap for a particular class
of protocols using a two-step procedure.
Numerical analysis shows that for other arbitrary protocols the states are also symmetrically
extendable throughout the gap. Moreover, for a very large percentage of protocols tested,
our two-step construction works. We thus have very strong evidence to believe that there
does not exist a two-way classical post-processing protocol to create a secret key beyond the
current bounds, so that there is a point beyond which classical correlations of quantum origin are no
longer useful in creating a secret key.
P2-259 Large-Scale Simulation of the Quantum Internet
Rodney Van Meter, Shigeya Suzuki, Shota Nagayama, Takahiko Satoh, Takaaki Matsuo,
Amin Taherkhani, Simon Devitt and Joe Touch
Abstract: The Quantum Internet (QI) will be a worldwide network of quantum repeater
networks, enabling quantum information services including entanglement-based
cryptographic functions such as quantum key distribution, secure distributed quantum
computation, and high-precision sensors. We are developing a large-scale simulator to study
109
the expected behavior and quantitatively evaluate solutions to the numerous design
problems. Our engineering methodology is to apply solutions developed in the Internet
community where possible. Our ultimate goal is simulation of ten thousand quantum
repeater nodes, organized into one hundred networks each comprising about hundred
nodes. At this scale, we expect to be able to study the macroscopic behavior of a Quantum
Internet and potentially see and examine emergent behavior that otherwise would not occur
until networks are deployed.
P2-261 Network-ready unconditional polarization qubit quantum memory at room
temperature
Eden Figueroa, Mehdi Namazi, Connor Kupchak, Bertus Jordaan and Reihaneh
Shahrokhshahi
Abstract: Here we study how the optical response of cold atomic environments is
transformed by the motion of atoms at room temperature and consequently characterize the
optimal performance of room temperature quantum light-matter interfaces. Our findings
enable us to attain complete quantum memory operation for polarization qubits in a warm
87Rb atomic vapor with an average fidelity
of 86.6%, thereby defeating any classical strategy exploiting the non-unitary character of the
memory efficiency. Our system significantly decreases the technological overhead required
to achieve quantum memory operation and will serve as a building block for scalable and
technologically simpler many-memory quantum machines
P2-262 Compact, integrated quantum key distribution sender module for hand-held
key exchange
Gwen Melen, Tobias Vogl, Markus Rau, Giacomo Corrielli, Andrea Crespi, Roberto
Osellame and Harald Weinfurter
Abstract: We report on the implementation of an integrated optics module (35x20x8mm3)
enabling to implement secure free-space key exchange in all optical communication
terminals. We demonstrate its maturity in the first key exchange with a hand-held Alice
system.
P2-263 Sub-Megahertz Single Photon Source
Markus Rambach, Aleksandrina Nikolova, Till J. Weinhold and Andrew G. White
Abstract: Hybrid quantum technologies seek to combine the advantages of two individual
quantum architectures by transferring the information between the two systems. We want to
benefit from the high mobility and ease of transmission of photons for quantum
communication and exploit the excellent readout and storage capabilities of atomic qubits as
a quantum memory, which is essential to build up quantum repeater networks for quantum
data processing. Efficient interaction of photons with atoms requires a match of the photons’
spectral properties to those of the resonances of the atomic species. The atomic transition
usually has a much narrower bandwidth than single photons generated by spontaneous
parametric down-conversion (SPDC), the current gold standard of producing high-purity
heralded single photons at flexible wavelengths. To develop hybrid quantum technologies
therefore requires significantly reducing the single photon emission spectra to fulfill these
requirements. The way we try to achieve this is by using an optical cavity to enhance the
probability of creating the photons in the spectral and spatial resonator mode.
110
Previous cavity-based SPDC sources have achieved bandwidths comparable to atomic
linewidths, but divide their operation time into stabilisation and photon production phases,
resulting in typical duty cycles < 50%. The so far narrowest photons from SPDC [1] have
bandwidths still well above a MHz and only one source has demonstrated 100% duty cycle
[2].
We report 100 % duty cycle generation of sub-MHz single photon pairs at the Rubidium D1
line using cavity-enhanced spontaneous parametric downconversion [3]. The double
exponential decay of the temporal intensity cross-correlation function exhibits a bandwidth of
66616 kHz for the single photons, an order of magnitude below the natural linewidth of the
target transition. This is, to our knowledge, the narrowest bandwidth of single photons from
SPDC to date. A new method of placing half-wave plate inside the cavity helps to achieve
triple resonance between pump, signal and idler photon, reducing the bandwidth and
simplifying the locking scheme. Additionally, stabilisation of the cavity to the pump frequency
enables the 100 % duty cycle. The narrow bandwidth in combination with the tunability
makes our system the perfect source for the future integration in gradient echo memories,
one of the most promising candidates for quantum memories to date, or hollow-core glass
fibers filled with rubidium gas to allow the construction of novel quantum logic gates. We
believe our new method of generating extremely narrow-band photons has the potential to
become a standard technique in the field of hybrid quantum technologies and will therefore
be of great interest to the field.
[1] J. Fekete, D. Rieländer, M. Cristiani, and H. de Riedmatten, Phys. Rev. Lett. 110, 220502
(2013).
[2] M. Scholz, L. Koch, and O. Benson, Phys. Rev. Lett. 102, 063603 (2009).
[3] M. Rambach, A. Nikolova, T. J. Weinhold, and A. G. White, arxiv: 1601.06173 (2016).
P2-265 Device-independent demonstration that a qubit is more than a quantum coin
Esteban S. Gómez, Santiago Gómez, Pablo González, Gustavo Cañas, Johanna F. Barra,
Aldo Delgado, Guilherme B. Xavier, Adán Cabello, Matthias Kleinmann, Tamás Vértesi and
Gustavo Lima
Abstract: Qubits are the simplest quantum systems and as such they have a pronounced
binary structure. Therefore, the qubit is sometimes compared to a »quantum coin« having
infinitely many sets of two sides which can only be tossed when specifying the desired set.
However, this picture fails to capture the richness of the quantum world and we here present
an experiment on pairs of polarization-entangled photonic qubits which cannot be explained
by two-outcome measurements. We combine this with device-independent evidence that the
system is best described by two qubits thus showing that quantum measurements on a qubit
are fundamentally non-binary and that the binary picture of the qubit thus cannot be uphold.
Since such measurements cannot be sharp, in addition this constitutes the first deviceindependent certification of a genuine generalized quantum measurement.
P2-266 Optimal Efficiency of Heat Engines with Finite-Size Heat Baths
Hiroyasu Tajima and Masahito Hayashi
Abstract: The optimal efficiency of quantum (or classical) heat engines whose heat baths are
$n$-particle systems is given by the information geometry and the strong large deviation. We
give the optimal work extraction process as a concrete energy-preserving unitary time
evolution among the heat baths and the work storage.
111
We show that our optimal work extraction turns the disordered energy of the heat baths to
the ordered energy of the work storage, by evaluating the ratio of the entropy difference to
the energy difference in the heat baths and the work storage, respectively. By comparing
the statistical machanical optimal efficiency with the macroscopic thermodynamical bound,
we evaluate the accuracy of the macroscopic thermodynamics with finite-size heat baths
from the statistical mechanical viewpoint. We also evaluate the quantum coherence effect
on the optimal efficiency of the cycle processes without restricting their cycle time, by
comparing the classical and quantum optimal efficiencies.
P2-267 Self-guaranteed measurement-based quantum computation
Masahito Hayashi and Michal Hajdusek
Abstract: We introduce a new verification protocol for measurement-only blind quantum
computation where the client can only perform single-qubit measurements and the server
has sufficient ability to prepare a multi-qubit entangled states. Previous such protocols were
limited by strong assumptions about the client's quantum devices. We remove these
assumptions by performing self-testing procedure to certify the initial entangled state
prepared by the server as well as the operation of the client's quantum devices. In the case
of an honest server and client's devices, the protocol produces the correct outcome of the
quantum computation. Given a cheating server or malicious quantum devices, our protocol
bounds the probability of the client accepting an incorrect outcome while introducing only
modest overhead in terms of the number of copies of the initial state needed that scales as
$O(n^4\log n)$, where $n$ is the size of the initial universal resource.
P2-268 Routing on a Quantum Internet
Takahiko Satoh, Shigeya Suzuki, Shota Nagayama, Takaaki Matsuo and Rodney Van Meter
Abstract: A routing algorithm is required in order to communicate across a multi-hop
network.
As with the Internet, in our design a Quantum Internet has a two-tier routing system: internal
routing within a homogeneous network known as a Quantum AS (QAS), and external
routingbetween heterogeneous networks, in an internetwork of QASes. As the number of
nodes grows, the traffic and computational cost of a routing protocol grow quickly. Thus, to
manage network heterogeneity, achieve scalability, and allow operational autonomy, a twotier system is needed. We are evaluating two options: a fully recursive structure and
quantum adapted BGP. To verify this scheme, we are progressing with the simulation of the
Quantum Internet that contains ten thousand quantum repeaters.
P2-269 Architecture of software simulation of a Quantum Internet
Shigeya Suzuki, Rodney Van Meter, Shota Nagayama, Takahiko Satoh and Takaaki Matsuo
Abstract: We have started development of a quantum repeater network simulator -QUISP. The goal of a quantum repeater network is to create a pair of
entangled qubits between two nodes specified by application initiated
by a user somewhere on the network. To build such a quantum repeater
network system, we want to estimate the cost to build it. In this
abstract, we discuss the key assumptions, the key design decisions
of the simulator.
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P2-270 Quantum Process Tomography of an Optically-Controlled Kerr Non-linearity
Bertus Jordaan, Connor Kupchak, Sam Rind and Eden Figueroa
Abstract: Any optical quantum information processing machine would be comprised of fullycharacterized constituent devices for both single state manipulations and tasks involving the
interaction between multiple quantum optical states. Ideally for the latter, would be an
apparatus capable of deterministic optical phase shifts that operate on input quantum states
with the action mediated solely by auxiliary signal fields. Here we present the complete
experimental characterization of a system designed for optically controlled phase shifts
acting on single-photon level probe coherent states. Our setup is based on a warm vapor of
rubidium atoms under the conditions of electromagnetically induced transparency with its
dispersion properties modified through the use of an optically triggered N-type Kerr nonlinearity. We fully characterize the performance of our device by sending in a set of input
probe states and measuring the corresponding output via time-domain homodyne
tomography and subsequently performing the technique of coherent state quantum process
tomography. This method provides us with the precise knowledge of how our optical phase
shift will modify any arbitrary input quantum state engineered in the mode of the
reconstruction.
P2-271 Entanglement assisted classical communication
communication” without causal order
Seiseki Akibue, Masaki Owari, Go Kato and Mio Murao
simulates
“classical
Abstract: Phenomena induced by the existence of entanglement, such as nonlocal
correlations, exhibit characteristic properties of quantum mechanics distinguishing from
classical theories. When entanglement is accompanied by classical communication, it
enhances the power of quantum operations jointly performed by two spatially separated
parties. Such a power has been analyzed by the gap between the performances of joint
quantum operations implementable by local operations at each party connected by classical
communication with and without the assistance of entanglement. In this work, we present a
new formulation for joint quantum operations connected by classical communication beyond
special relativistic causal order but without entanglement and still within quantum mechanics.
Using the formulation, we show that entanglement assisting classical communication
necessary for implementing a class of joint quantum operations called separable maps can
be interpreted to simulate "classical communication" not respecting causal order. Our results
reveal a new counter-intuitive aspect of entanglement related to spacetime.
P2-273 Quantum information applications of highly ordered stoichiometric rare earth
crystals
Rose Ahlefeldt, Michael Hush and Matthew Sellars
Abstract: We propose the use of stoichiometric rare earth crystals for quantum information
applications. In addition to the long coherence times characteristic of rare earth ions, these
materials have high spatial and spectral densities of ions, and a highly ordered rare earth
lattice. These properties allow improvements in quantum memory performance, and new
applications that have not previously been considered for rare earth lattice. In particular,
when the optical inhomogeneous broadening is smaller than both the hyperfine structure and
the ion-ion interaction strength, quantum many body effects will be visible, including
excitation blockade, which has never before been seen in a the solid state. We show that
this regime is reachable in current materials by using isotopic purification to reduce the
crystalline disorder, and demonstrate this method for EuCl3.6H2O, achieving a linewidth of
113
25 MHz, well below both the hyperfine structure and dominant interaction strength. We
discuss the use of this material for quantum memory implementations and many body
studies.
P2-274 One-way quantum computing with arbitrarily large time-frequency continuousvariable cluster states from a single optical parametric oscillator
Rafael Alexander, Pei Wang, Niranjan Sridhar, Moran Chen, Olivier Pfister and Nicolas
Menicucci
Abstract: One-way quantum computing is experimentally appealing because it requires only
local measurements on an entangled resource called a cluster state. Record-size, but nonuniversal, continuous-variable cluster states were recently demonstrated separately in the
time and frequency domains. We propose to combine these approaches into a scalable
architecture in which a single optical parametric oscillator and simple interferometer entangle
up to (3 x 10^3 frequencies) x (unlimited number of temporal modes) into a computationally
universal continuous-variable cluster state.
P2-276 Randomized benchmarking with cluster states
Rafael Alexander, Peter Turner and Stephen Bartlett
Abstract: In measurement-based quantum computation, once a universal resource state can
be generated then in principle computation can proceed via single-site measurements only.
However, unless the errors in elementary gate operations are sufficiently low, the
computation will not be fault-tolerant. Here we generalize the randomized benchmarking
protocol for a single-qubit to a linear cluster state computation, which provides partial, yet
efficient characterization of the noise associated with the target gate set. We consider two
different approaches: the first makes uses the single-qubit Clifford group (the standard 2design for randomized benchmarking). The second approach uses recently introduced
measurement-based 2-designs, which relies on the intrinsic randomness of measurementbased quantum computation in order to generate random elements.
P2-277 Simple approximation of minimum error probability for pure-state signals
Tsuyoshi Usuda and Shungo Asano
Abstract: To compute the minimum error probability is indispensable for estimating
performance of a quantum communication system and security of a quantum cryptographic
protocol. However, even if the optimum measurement and the analytical expression of the
minimum error probability are known, computation is hard when the number of quantum
signals is extremely large. In the previous study, we proposed a simple and easily
computable approximation of the minimum error probability. In this presentation, we
demonstrate the approximation and show extended versions. The extended versions of
approximation is shown to be more accurate than the original version. We also give
numerical results of the approximation for various signals, e.g. binary signals coded by linear
codes.
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P2-280 Determining the Quantum Fisher Information from Linear Response Theory
Tomohiro Shitara and Masahito Ueda
Abstract: The quantum Fisher information is characterized as a metric on the space of
quantum states that monotonically decreases under quantum operations, and gives an
upper bound on the accuracy of state estimation. Due to the noncommutative nature of
quantum theory, there exist infinitely many types of the quantum Fisher information. The
operational meanings of each quantum Fisher information beyond the monotonicity have
been investigated individually, and even how it is related to observable quantities has not
been revealed yet. We propose a method of determining a general quantum Fisher
information using the linear response theory in statistical mechanics. We generalize the
fluctuation-dissipation theorem, which connects the linear response function with the
generalized covariance in the frequency domain. Based on this theorem, we can determine
the generalized covariance from the admittance, which is an experimentally measurable
quantity. Since the generalized covariance is an equivalent description of the quantum
Fisher information, we can also experimentally determine the quantum Fisher information by
measuring the admittance.
P2-282 Cooling of a one-dimensional Bose gas
Bernhard Rauer, Pjotrs Grisins and Jörg Schmiedmayer
Abstract: We experimentally study the dynamics of a degenerate one-dimensional Bose gas
that is subject to a continuous outcoupling of atoms. Although standard evaporative cooling
is rendered ineffective by the absence of thermalizing collisions in this system, we observe
substantial cooling. This cooling proceeds through homogeneous particle dissipation and
many-body dephasing, enabling the preparation of otherwise unexpectedly low
temperatures. Our observations establish a scaling relation between temperature and
particle number, and provide insights into equilibration in the quantum world.
P2-283 Concepts of non-Markovianity: a quantum hierarchy
Li Li, Michael Hall and Howard Wiseman
Abstract: The evolution of a closed quantum system is completely determined by the
Schrodinger equation. In contrast, the dynamics of an open quantum system are influenced
by its environment. As no physical system is truly isolated, this is a situation which applies
very widely, and is an important consideration as diverse as atomic physics, optics and
quantum information. There has been significant recent interest in characterizing nonMarkovian processes for open quantum systems. These have primarily centred on two new,
closely-related formal approaches: distinguishability and divisibility. The first approach
defines non-Markovianity as an increase in the distinguishability of system states, relative to
some measure such as trace distance or relative entropy. The second approach is again
solely formulated in terms of the system dynamical map, and requires this map to be
“divisible” into completely positive maps connecting the system states at different times.
However, more broadly, a general consensus as to the `correct' approach to quantum
Markovianity is still very much missing, and it remains a controversial issue. The main aim of
our work is to significantly clarify and bring order to the debate, by reviewing a large number
of physical concepts that either have been, or could reasonably be, used to define quantum
Markovianity, and proving a number of hierarchical relations between them.
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P2-284 Topological pumping of photons in nonlinear coupled resonator arrays
Jirawat Tangpatinanon, Victor Bastidas, Dimitris Angelakis
Abstract: Topological pumping allows the robust transport of quantum particles in a 1D
periodic lattices. The pumping is implemented by adiabatic and cyclic deformation of the
Hamiltonian. In contrast to conventional 2D topological materials, the 1D material can be
thought of as having (1+1) dimensions, where time acts as an extra dimension with periodic
boundary conditions. Hence, the topology of the effective 2D system can be associated with
the Chern number, resulting in transport properties which are robust against small
perturbations. In this work, we propose a realization of such pump using photons in
nonlinear coupled resonator arrays, where the frequency of the resonator is periodically
modulated in space and time. In contrast to the linear regime, inherent nonlinearity in our
model enables the robust transport of Fock state with few photons per site. We show that
signatures of such topological pumping can be observed in a lossy array, as small as nine
sites. This brings such signatures into the realm of observability in existing circuit
QED technologies.
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Program at a Glance
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