Download Analog Quantum Simulators - Kirchhoff

International Workshop on
Analog Quantum Simulators
for many-body dynamics
AQuS 2016
Internationales Wissenschaftsforum
Universität Heidelberg
September 05-08, 2016
Programme
& Abstracts
Topics
Quantum simulaton, certfcaton, robustness, and complexity
Quantum simulaton of contnuous and latce atomic gases
Exciton-Polariton condensates and their dynamics
Quantum fuids of light
Universality out of equilibrium
Analog gravity
Informaton
htps://www.kip.uni-heidelberg.de/aqus/aqus2016/
Horizon 2020 FET-Proactve Consortum AQuS – Partners: Universität Heidelberg (Coordinator),
LPN-CNRS Marcoussis, FU Berlin, INO-CNR Trento, LMU München, U Cambridge & TU Wien
Scientfc Board
Alberto Amo (Marcoussis)
Jürgen Berges (Heidelberg)
Jacqueline Bloch (Marcoussis)
Iacopo Carusoto (Trento)
Jens Eisert (Berlin)
Thomas Gasenzer (Heidelberg)
Markus Oberthaler (Heidelberg)
Jörg Schmiedmayer (Wien)
Ulrich Schneider (Cambridge/LMU)
Coordinaton
Thomas Gasenzer
Funded by the Horizon 2020
Framework Programme of
the European Union
text
Programme
Monday, 5 September 2016
11:10 Opening
Chair: Markus Oberthaler
Bose-Einstein Condensation of
Photons and Periodic Potentials
for Light
Quantum Fisher information as
efficient entanglement witness in
many-body systems
11:30 Martin Weitz (Bonn)
12:10 Philipp Hauke (Innsbruck)
12:50 Lunch
Chair: Tomaž Prosen
14:30 Fabian Essler (Oxford)
Thermalization and light cones in
a model with weak integrability
breaking
15:10 Jean-Sébastien Caux (Amsterdam) Dynamics and relaxation in
integrable quantum systems
15:50 Coffee/Tea
Chair: Martin Weitz
Quantum simulations with trapped
ions
16:30 Petar Jurcevic (Innsbruck)
17:10 Evening at free disposition
3
Tuesday, 6 September
Chair: Alberto Amo
Dissipative dynamics and quantum
state engineering with ultracold
atoms
Thermal quenches in the
stochastic Gross-Pitaevskii
equation: morphology of the
vortex network
09:00 Andrew Daley (Strathclyde)
09:40 Leticia Cugliandolo (Paris)
10:20 Coffee/Tea
Chair: Leticia Cugliandolo
Quantum critical phenomena in
open lattice systems
Correlations in nonequilibrium
polariton quantum fluids
11:10 Cristiano Ciuti (Paris)
11:50 Michiel Wouters (Antwerpen)
12:30 Lunch
Chair: Fabian Essler
Exactly solvable open many-body
systems
Synthetic dimensions in ultracold
atoms and photonics
14:30 Tomaž Prosen (Ljubljana)
15:10 Tomoki Ozawa (Trento)
15:50 Coffee/Tea
Chair: Michiel Wouters
Out of equilibrium condensation in
polariton lattices
16:30 Alberto Amo (Marcoussis)
18:00 Dinner buffet and Posters
4
Wednesday, 7 September
Chair: Andrew Daley
Ultracold Dysprosium gases: a
complex system from radiative
trapping to many-body physics
Out of equilibrium dynamics of
ergodic and disordered systems
and the quest for quantum
supremacy for quantum simulators
09:00 Silvain Nascimbène (Paris)
09:40 Jens Eisert (Berlin)
10:20 Coffee/Tea
11:10 Austen Lamacraft (Cambridge)
11:50 Henrik Lüschen (Cambridge)
Chair: Jens Eisert
Weak Many Body Localization in
the Quantum Random Energy
Model
Experimental Results on
Many-Body Localization
12:30 Lunch
Chair: Silvain Nascimbène
From collectives excitations to
turbulence in a uniform Bose gas
From Quenches to Critical
Dynamics and Non-Thermal Fixed
Points in Ultracold Bose Gases
14:30 Nir Navon (Cambridge)
15:10 Markus Karl (Heidelberg)
15:50 Coffee/Tea
Chair: Ulrich Schneider
Investigating ultracold atom
systems with higher order
correlation functions in and out of
equilibrium
Non-equilibrium dynamics of
long-range interacting Rydberg
systems
16:30 Thomas Schweigler (Wien)
17:10 Adrien Signoles (Heidelberg)
17:50 Evening at free disposition
5
Thursday, 8 September
Chair: Jörg Schmiedmayer
Bose and Fermi polarons in
ultracold atoms
Simulating quantum fields
09:00 Eugene Demler (Harvard)
09:40 Tobias Osborne (Hannover)
10:20 Coffee/Tea
Chair: Eugene Demler
Analog Hawking physics in atomic
and optical systems
11:10 Iacopo Carusotto (Trento)
12:30 Closing and Departure
6
Practical Information
The local participants will wear a green sticker on their name tag. They will answer
any practical questions you may have.
Location
The conference hall is in the Internationales Wissenschaftsforum Heidelberg (IWH),
situated in the old town of Heidelberg at the foot of the castle hill. The address is the
following:
Internationales Wissenschaftsforum Heidelberg
Hauptstrasse 242
D-69117 Heidelberg
The public transport station that is closest is “S-Bahnhof Altstadt”. It can be reached
with the S-Bahn (lines S1 and S2) or the bus (line 33). Then it’s a 3 minutes walk in
direction of the city centre to reach the IWH.
The nearest parking opportunities are "Parkhaus 13" at the "Karlsplatz" (17.50 € per
day) and "Parkhaus 12" at the "Kornmarkt" (13.50 € per day). It is a 3-minute walk
from there to the IWH.
For more information, please look up the local public transportation and German railway
Internet pages:
http://www.vrn.de
http://www.bahn.com
Transportation to and from Frankfurt airport can be found at:
http://frankfurt-airport-shuttles.de/en/home-2/
https://www.tls-heidelberg.de/en/
There is also map with many useful annotations at:
http://g.co/maps/jt46s
A small map can be found at the end of this booklet.
Internet
There is a wifi Internet access in the conference hall. Connect to WLAN ’UNIWEBACCESS’ and open your browser. It will automatically redirect to the login page.
login and password: see note on whiteboard in the lecture room
The web-page of the conference is: https://www.kip.uni-heidelberg.de/aqus/aqus2016/
7
8
Talks
Bose-Einstein Condensation of Photons and Periodic
Potentials for Light
Martin Weitz
Institut für Angewandte Physik, Universität Bonn, D-53115 Bonn
Bose-Einstein condensation has been observed with cold atomic gases, quasiparticles
in solid state systems as polaritons, and more recently also with photons in a dye-filled
optical microcavity. I will here describe measurements of our Bonn group determining
the coherence of a photon Bose-Einstein condensate and realizing periodic potentials
for the optical quantum gas. The optical condensate is generated in a wavelength-sized
optical cavity, where the small mirror spacing imprints a low-frequency cutoff with a
spectrum of photon energies restricted to well above the thermal energy. The cavity
mirrors provide a trapping potential and a non-vanishing effective photon mass, making
the system formally equivalent to a two-dimensional gas of trapped massive bosons.
Thermalization of the photon gas is reached in a number conserving way by repeated
absorption re-emission cycles in the dye molecules. Recent experiments realizing periodic lattice potentials for the photon gas will be reported, as well as measurements
investigating the competition of tunneling and effective photon interactions in doublewell potentials.
9
Quantum Fisher information as efficient
entanglement witness in many-body systems
Philipp Hauke
Institute for Theoretical Physics, University of Innsbruck, Austria
Entanglement is considered a resource for quantum simulation, but it is difficult to
quantify experimentally in a many-body setting. Here, we discuss scenarios where
many-body entanglement becomes accessible via the quantum Fisher information, a
known witness for genuinely multipartite entanglement. First, we introduce a direct
relation of the QFI in thermal states with linear response functions, which makes the
QFI measurable with standard methods. Using this relationship, we show that close to
continuous quantum phase transitions the QFI, and thus multipartite entanglement, is
strongly divergent. Second, we demonstrate that the quantum Fisher information can
witness many-body localized phases, showing a characteristic growth of entanglement
at long times after a quantum quench. These results illustrate that the quantum Fisher
information represents a useful and efficiently measurable witness for entanglement in
quantum many-body settings.
Thermalization and light cones in a model with weak
integrability breaking
Fabian Essler
The Rudolf Peierls Centre for Theoretical Physics, University of Oxford, United
Kingdom
I discuss the application of equation of motion techniques to study the non-equilibrium
dynamics in a class of lattice models of weakly interacting spinless fermions. Our
model provides a simple setting for analyzing the effects of weak integrability breaking
perturbations on the time evolution after a quantum quench.
10
Dynamics and relaxation in integrable quantum
systems
Jean-Sébastien Caux
Institute of Physics, University of Amsterdam, The Netherlands
This talk will outline integrability-based results on the out-of-equilibrium dynamics of
low-dimensional systems such as interacting atomic gases and quantum spin chains. A
number of recent developments will be explained, including a new method for explicitly
calculating the relaxation of observables after a quantum quench. Exact solutions
to the interaction turn-on quench in the Lieb-Liniger model and to the Néel-to-XXZ
quench in spin chains will be presented. Particular emphasis will be given to interesting
open issues, including the failure of the (local) Generalized Gibbs Ensemble to properly
describe post-quench steady-state properties and the necessity to include quasilocal
conserved charges to obtain correct answers.
Quantum simulations with trapped ions
Petar Jurcevic
Institut für Experimentalphysik, Universtität Innsbruck, Austria
11
Dissipative dynamics and quantum state engineering
with ultracold atoms
Andrew Daley
Department of Physics, University of Strathclyde, Glasgow, United Kingdom
The time-dependent microscopic control available over systems of ultracold atoms has
opened new opportunities to explore many-body dynamics, addressing fundamental
questions both in and out of equilibrium. As always in such systems, a key experimental
challenge is found in the need to cool systems to lower temperatures. However, the
time-dependent control available over these dynamics can provide a new tools for
realising low-entropy many-body states, and this is further enhanced by the possibility
to generate dissipative dynamics that are also well understood on a microscopic level.
I will discuss recent developments in this area, illustrated with our recent theoretical
work in two directions: (i) the generation of spin-entangled states of fermionic atoms in
an optical lattice by combining Fermi statistics with dissipation induced by a reservoir
gas not trapped by a lattice, and (ii) the application of bilayer lattice systems, together
with dynamical control of atoms in optical lattices, to dynamically disentangle two
subsystems and achieve sensitive many-body states via adiabatic cooling.
12
Thermal quenches in the stochastic Gross-Pitaevskii
equation: morphology of the vortex network
Leticia Cugliandolo
Laboratoire de Physique Théorique et Hautes Energies, Sorbonne Universités Université Pierre et Marie Curie
A system taken across a second order phase transition from its disordered into its
symmetry-broken phase undergoes a phase ordering process. Topological defects are
left in the system at finite times after the quench and, in open systems, they are
gradually eliminated in the course of evolution towards equilibrium.
I will discuss a recent detailed study of the evolution of 3d weakly interacting bosons at
finite chemical potential, taken across their phase transition, using the stochastic GrossPitaevskii equation. In short, I will explain the full characterisation of the vortex network
in and out of equilibrium. This is work in collaboration with Michikazu Kobayashi
(Kyoto University).
Quantum critical phenomena in open lattice systems
Cristiano Ciuti
Univ. Paris Diderot, Paris, France
In this invited talk, I will present recent theoretical results of my group about nonequilibrium critical phenomena in open quantum systems. In particular, I will show
predictions for driven-dissipative photonic systems and also dissipative spin lattices.
13
Correlations in nonequilibrium polariton quantum
fluids
Michiel Wouters
Universiteit Antwerpen, Antwerpen (Wilrijk), Belgium
Microcavity polaritons interact much stronger than photons, but can still be safely
described by the Bogoliubov approximation. I will discuss the coherence properties
of both resonant and nonresonantly excited polariton condensates. For the case of
pulsed resonant excitation, connections to the dynamical Casimir effect and quenches
in many-body systems can be made.
Exactly solvable open many-body systems
Tomaž Prosen
Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
I will discuss several examples of one-dimensional interacting open quantum many-body
systems for which one can write exact solution for the steady state, or even compute
the full Liouvillian spectrum of decay modes. Among the most prominent ones are the
boundary driven XXZ and fermi Hubbard chains, the former displaying a non-equilibrium
quantum phase transition in the steady state, while the full spectrum of the XX chain
with de-phasing bulk noise and possible boundary driving can be shown to be equivalent
to Bethe-ansatz spectrum of the Hubbard model with imaginary interaction U.
14
Synthetic dimensions in ultracold atoms and
photonics
Tomoki Ozawa
Dipartimento di Fisica, INO-CNR BEC Center and University of Trento, Povo (TN),
Italy
I discuss recent developments of the study of “synthetic dimensions” in ultracold gases
and photonics. The idea of synthetic dimensions is to identify internal states of an
atom or a photonic cavity as extra dimensions, and to simulate higher dimensional
lattice models using physically lower dimensional systems. The concept was originally
proposed and experimentally realized in ultracold gases. I first review the existing
theoretical and experimental studies of synthetic dimensions. After discussing some
challenges and limitations of the existing methods of synthetic dimensions, I explain
our proposals of realizing synthetic dimensions both in ultracold gases and in photonic
cavities, which overcome some of these limitations. Finally I discuss how the four
dimensional quantum Hall effect can be observed in ultracold gases and photonics
using the synthetic dimensions.
15
Out of equilibrium condensation in polariton lattices
F. Baboux1 , D. De Bernardis2 , C. Gomez1 , E. Galopin1 , A. Lemaître1 , L.
Le Gratiet1 , I. Sagnes1 , A. Amo1 , M. Wouters1 , J. Bloch1,3
1
2
Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université
Paris-Saclay, C2N Marcoussis, 91460 Marcoussis, France
Theory of Quantum and Complex Systems, Universiteit Antwerpen, Universiteitsplein
1, B-2610 Antwerpen, Belgium
3
Physics Department, École Polytechnique, F-91128 Palaiseau Cedex, France
Exciton polaritons in semiconductor microcavities provide an excellent platform to
study the out-of-equilibrium properties of interacting quantum fluids. An important
characteristic of polariton condensates is that they coexist with a bath of reservoir
particles at high energies in a far-from-thermal state [1]. The combination of bosonic
stimulation with the interactions between condensed and non-condensed polaritons
results in an effective attractive interaction [2]. This gives rise to strong instabilities
that destroy the polariton condensate when using large excitation spots []. Here we
will show evidence of this instability and how polariton condensates can become stable
in a periodic lattice. The stabilisation of polariton condensates demonstrated in this
work, opens a new paradigm in polariton physics, allowing the exploration of the
Kardar–Parisi–Zhang physics, and provide a route for the spatial engineering of the
sign of the interactions.
[1] F. Baboux et al., Bosonic Condensation and Disorder-Induced Localization in a Flat
Band. Phys. Rev. Lett. 116, 066402(2016).
[2] N. Bobrovska, E. A. Ostrovskaya, and M. Matuszewski, Stability and spatial coherence of nonresonantly pumped exciton-polariton condensates. Phys. Rev. B 90,
205304 (2014).
[3] K. S. Daskalakis, S. A. Maier, and S. Kéna-Cohen, Spatial Coherence and Stability
in a Disordered Organic Polariton Condensate. Phys. Rev. Lett. 115, 035301 (2015).
16
Ultracold Dysprosium gases: a complex system from
radiative trapping to many-body physics
Sylvain Nascimbène
LKB ENS Paris, Laboratoire Kastler Brossel, Collège de France, Paris, France
Atomic Dysprosium features a complex electronic structure, which leads to several interesting properties in the context of atomic physics: a large electronic angular momentum, a large magnetic moment, many narrow optical transitions. Those characteristics
imply specific physical behaviors, from the radiative cooling and trapping to the design
of novel schemes for quantum many-body physics.
We will first present a detailed study of the magneto-optical trapping (MOT) of ultracold Dysprosium. We will show that the MOT can be operated in several regimes,
with either all or a single Zeeman components involved. Due to the weak radiative
forces obtained with a narrow optical transition, gravity plays an major role, and tends
to polarize the atomic sample. We will also discuss light-induced inelastic collisions.
The second part of the talk will address the prospects of our experiment, which aims
at realizing topological superfluids with ultracold Dysprosium. We will show that the
structure of optical transitions is well suited for realizing light-induced gauge fields,
the basic ingredient for realizing a topological superfluid. We will also present several
schemes to reveal the presence of Majorana fermions at the edges of the topological
superfluid.
17
Out of equilibrium dynamics of ergodic and
disordered systems and the quest for quantum
supremacy for quantum simulators
Jens Eisert
Dahlem Center for Complex Quantum Systems, Freie Universität Berlin,
Berlin-Dahlem, Germany
Dynamical analogue quantum simulators allow to probe a plethora of physical phenomena related to the physics of quantum systems out of equilibrium. In this talk, we
will consider questions of equilibration, Gaussification, the dynamics of quantum phase
transitions and the absence of thermalisation - present in disordered interacting models
that show features of the multi-faceted phenomenon of many-body localisation. We
discuss both new theoretical results, as well as tools employed in collaborations with
experimentalists working with cold atoms in optical lattices and on atom chips.
In the last part of the talk, we will have a look at work in progress on conceptual
questions that seem to be key to the idea of a quantum simulator: This in on the one
hand one of how to devise quantum simulators that have the potential of computationally outperforming classical devices, discussing variants of IQP circuits. On the other
hand, it the question of the certification of quantum simulators for which no classical
simulation algorithm is known.
Weak Many Body Localization in the Quantum
Random Energy Model
Austen Lamacraft
Cavendish Laboratories, University of Cambridge, United Kingdom
18
Experimental Results on Many-Body Localization
Henrik Lüschen
Fakultät für Physik, Max Planck Institute of Quantum Optics, München, Germany
The phenomenon of many-body localization (MBL) describes a generic nonthermalizing phase in which quantum information can persist locally up to infinite
times. MBL is separated from a phase obeying the eigenstate-thermalization hypothesis via a disorder driven dynamical phase transition, which happens not only in the
ground state but over an extended range of energy densities. An effect similar to finite
temperatures smearing out ground state phase transitions into universal crossovers is
expected in the presence of a small coupling to an external heat bath.
I will present recent experimental results on the MBL phase transition, as well as MBL
in the presence of a weak photon bath, based on the relaxation of fast local observables
in a quasi-random optical lattice. We find slow powerlaw dynamics close to the MBL
critical point, which is potentially connected to Griffith type effects. Also, in the
presence of controllable weak photon scattering, we observe restoration of ergodicity
on a timescale dependent on the microscopic parameters of the Hamiltonian.
19
From collectives excitations to turbulence in a
uniform Bose gas.
Nir Navon
University of Cambridge, United Kingdom
The recent realisation of Bose-Einstein condensates in uniform traps has opened interesting possibilities to study far-from-equilibrium phenomena with textbook systems. In
this talk, we will present a study where we drive a homogeneous Bose-Einstein condensate (BEC) out of equilibrium with an oscillating force that pumps energy into the
system at the largest lengthscale. In the limit of weak drives, the BEC’s response is
linear, well captured by its lowest-lying excitations. For stronger drives, a nonlinear
response is apparent and we observe a gradual development of a cascade characterised
by an isotropic power-law distribution in momentum space. We will report on our latest
progress on the detailed characterisation of the steady-state turbulent state, as well as
a joint experimental/theoretical investigation into the finite-temperature behaviour of
the BEC lowest-lying mode.
20
From Quenches to Critical Dynamics and
Non-Thermal Fixed Points in Ultracold Bose Gases
Markus Karl
Kirchhoff Institut für Physik, Universität Heidelberg, Deutschland
Ultracold quantum gases provide a vast playground for exploring dynamical critical phenomena, such as phase transitions and universal scaling far from equilibrium. Here, we
consider one- and multi-component (spin) systems of ultracold Bose gases, inducing
highly non-linear dynamical evolution via sudden parameter quenches and instabilities. We identify critical scaling and universal scaling forms in the post-quench time
evolution of the respective systems. For quenches within the symmetric phase of a
two-component Bose gas, we show that shorttime quench dynamics can be described
by a universal crossover function, where the quench-induced energy appears as the relevant energy scale. Scaling properties have been found which indicate the importance
of pre-thermalisation temperatures long before dephasing has occurred in the nearly
gapless system. We discuss the theoretical results in the light of and illustrated by
recent experimental measurements. For the single-component gas, we find a new universal phase of time evolution, characterised by an anomalously slow, glass-like, phase
ordering process of vortex defects in the symmetry-broken phase. We discuss our results, in particular, for dynamical universal scaling forms in the light of the concept of
non-thermal fixed points.
21
Investigating ultracold atom systems with higher
order correlation functions in and out of equilibrium
Thomas Schweigler
Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Austria
We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids,
which realize the quantum sine-Gordon model relevant for a wide variety of disciplines
from particle to condensed-matter physics. From measured interference patterns we
extract phase correlation functions and analyze if, and under which conditions, the
higher-order correlation functions factorize into lower ones. This allows us to characterize some essential features of the model solely from our experimental measurements.
The method is also used to investigate the non-equilibrium dynamics following a quench
in the tunnel-coupling strength between the superfluids.
Non-equilibrium dynamics of long-range interacting
Rydberg systems
Adrien Signoles
Physical Institute, Heidelberg University, Germany
Rydberg atoms in ultracold gases constitute controllable systems to experimentally
study non-equilibrium phenomena. Of specific interest is the possibility to introduce
resonant dipolar exchange interactions. This provides new opportunities for investigating the dynamics of strongly correlated many-body quantum systems with beyondnearest neighbour coupling.
Here we present an experimental realization of such a system, by exciting nS and nP
Rydberg states and coupling them with microwave fields, which allow for studying dynamics of correlated spin systems. We report the observation of interaction-induced
effects in the dynamics of this ensemble of atoms and show that the system can be
understood in terms of a dipolar XX model, providing a benchmark for spin systems. I
will review recent theoretical and experimental progress in the study of Bose and Fermi
polarons in ultracold atoms. The emphasis will be on understanding non-equilbrium
aspects such as dynamics of polaron formation probed by Ramsey interferometry
22
Bose and Fermi polarons in ultracold atoms
Eugene Demler
Harvard University, Cambridge, MA 02138, USA
I will review recent theoretical and experimental progress in the study of Bose and Fermi
polarons in ultracold atoms. The emphasis will be on understanding non-equilbrium
aspects such as dynamics of polaron formation probed by Ramsey interferometry
Simulating quantum fields
Tobias Osborne
Institut für Theoretische Physik, Leibniz Universität Hannover, Germany
During the past decades we have seen important hints coming from string theory and
holography – particularly in the study of 4D SUSY gauge theories – that the parametrisation of QFTs in terms of lagrangians via the path integral is not always the most
efficient representation. Thus, given the success of tensor networks in condensed matter theory, it seems worthwhile to contemplate how to formulate QFT directly in terms
of a state represented as a TNS. Doing this directly suggests new quantum simulation
algorithms for interacting quantum fields. In this talk I will describe the modern Wilsonian approach to defining QFT and explain how to implement this approach directly in
terms of TNS and describe how to take the continuum limit of tensor networks ranging
from matrix product states, projected entangled pair states, tree tensor networks, and
the multiscale entanglement renormalisation ansatz. These continuum limits then form
the basis for quantum simulation algorithms, both analog and discrete, which allow for
a direct comparison between the simulation results coming from discretisations and the
desired continuum theory.
23
Analog Hawking physics in atomic and optical
systems
Iacopo Carusotto
BEC Trento, INO-CNR BEC Center, 38123 Povo (Trento), Italy
In this talk I will present the latest advances of the AQuS project in the study of analog
models of black holes using condensed matter and optical systems.
In the first part of the talk, I will focus on the stimulated and spontaneous Hawking
emission of phonons in a flowing fluid of polaritons in a semiconductor microcavity
and I will outline the perspectives in view of an experimental observation. I will then
review on-going theoretical studies of the consequences of the non-equilibrium condition
on the quantum properties of the Hawking emission polariton fluids, and of Hawking
emission in atomic gases with spin degrees of freedom or trapped in a elongated twowell potential. I will conclude with an outline of more speculative investigations in
the direction of highlighting the back-reaction effect of Hawking emission onto the
condensate motion.
24
Posters
Exploring few-fermion systems in single- and
multi-well potentials
A. Bergschneider , V. M. Klinkhamer, J. H. W. Becher,
M. Dehabe, G. Zürn, P. M. Preiss and S. Jochim
Physikalisches Institut der Universität Heidelberg, 69120 Heidelberg, Germany
We present several measurements that use ultracold fermionic atoms to investigate the
crossover from few to many-body physics in different kinds of quantum systems. The
measurements follow a bottom-up approach: We first generate and control the smallest
realization that contains the relevant physics and then gradually increase the size of
the system.
With our setup, we can generate one or several cigar-shaped potentials to trap ultracold
atoms. We deterministically prepare few fermions in these potential wells with full
control over the particle number and the quantum state of the system. Furthermore,
we can tune the interparticle interactions between the fermions over a large range.
In a first set of experiments we studied the transition from few- to many-body physics
in a one-dimensional system. We prepared a single impurity and an increasing number
of majority particles in a single well and studied the interaction energy as a function of
the number of majority atoms [1]. We also realized few-particle antiferromagnetic spin
chains by starting with noninteracting two-component systems in one well and ramping
to strong repulsion [2].
Recently, we prepared two fermions in the ground state of a double-well potential and
demonstrated full control and tunability of this system without increasing its entropy.
This system can be considered as the fundamental building block of the Fermi-Hubbard
model. Combining several double wells can allow to prepare low-entropy states in a
few-site lattice [3].
[1] A. N. Wenz et al., Science 342, 457(2013).
[2] S. Murmann et al., in preparation.
[3] S. Murmann et al., PRL 114, 080402 (2015).
25
Black-Hole lasing in spinorial condensates
Salvatore Butera
Heriot-Watt University, Edinburgh, United Kingdom
We study the analogue of the Hawking radiation physics in a coherently coupled two
component Bose-Einstein condensate. In practice, we consider a gas of two level atoms,
whose internal states are coupled by an external laser field. Both for the homogeneous
and the harmonically trapped (quasi-) one-dimensional system we show, by properly
tuning the mean-field coupling constants and the Rabi frequency of the light-atoms
interaction, the occurrence of the black-hole lasing effect respectively in the density
and in the spin-density branches of the fluctuation field.
The advantage of considering this set-up relies on the high controllability of the parameters of the light-atoms interaction in state-of-the-art cold-atom experiments and
on the fact that, coupling the internal states by a two-photons Raman interaction,
the inhomogeneity of the laser-atom interaction do not locally modify the chemical
potential of the system, which remain homogeneous over all the condensate without
the necessity of opportunely tailoring the external confining potential.
Topological Varma superfluid in optical lattices
Marco Fedele Di Liberto
INO-CNR BEC Center Trento, 38123 Povo (Trento), Italy
Topological states of matter are peculiar quantum phases showing different edge and
bulk transport properties connected by the bulk-boundary correspondence. While noninteracting fermionic topological insulators are well established by now and have been
classified according to a ten-fold scheme, the possible realisation of topological states for
bosons has not been much explored yet. Furthermore, the role of interactions is far from
being understood. Here, we show that a topological state of matter exclusively driven
by interactions may occur in the p-band of a Lieb optical lattice filled with ultracold
bosons. The single-particle spectrum of the system displays a remarkable parabolic
band-touching point, with both bands exhibiting non-negative curvature. Although the
system is neither topological at the single-particle level, nor for the interacting ground
state, on-site interactions induce an anomalous Hall effect for the excitations, carrying
a non-zero Chern number. Our work introduces an experimentally realistic strategy for
the formation of interaction-driven topological states of bosons.
26
Far from equilibrium integrable systems
Sebastian Erne
Institute for theoretical Physics, Heidelberg University, Germany
Relaxation of far-from equilibrium integrable systems is to date an open and interesting
question. Recent progress in cold atom experiments in low dimensional systems, allow
for a detailed study of integrable field theories. Specifically we consider a system of
linearly coupled quasi one-dimensional condensates, realizing the quantum sine-Gordon
and Lieb-Liniger theories. By studying quenches in the sine-Gordon model, we are
able to explore fundamental questions of quantum physics. In particular we investigate prethermalization and the Generalized Gibbs Ensemble, higher order correlations
and their factorization properties in and out of equilibrium, dynamics and decay of
topological excitations and false vacua, quantum many body revivals, and tomography of quasiparticle. We compare the experiment to analytical and numerical results,
for the latter using the (stochastic) Gross-Pitaevskii equations as well as Monte-Carlo
simulations.
27
Verify Many-Body Entanglement via Structure
Factor Measurements
Oliver Marty
Institut für Theoretische Physik, Universität Ulm, Germany
A fascinating example of a genuine quantum effect is the concept of spin-squeezing that
describes a collective property of an aggregation of spins. Since its first consideration
in the context of quantum metrology a central application of spin-squeezing parameters
became the detection of multipartite quantum correlations, that is, quantitatively the
degree of spin-squeezing is a measure of multipartite entanglement. Entanglement
criteria based on spin-squeezing parameters benefit from the fact that these parameters
usually depend on simple and global observables only, in particular, typically on loworder moments of collective spin operators. As a consequence, the approach provides
an experimentally easily accessible and robust way for entanglement detection that is
free of any assumptions on the system and may therefore be suitable for many different
platforms. Motivated by a criteria of Sorensen and Molmer [PRL 86, 4431 (2001)]
for multipartite entanglement, our contribution is a general scheme, that allows for
the detection of many-body entanglement via a variety of observables. As an example
we present entanglement criteria based on the structure factor, an observable which
can be measured in neutron scattering experiments, but may also be accessible on
other platforms such as trapped ions. To explicitly obtain the criteria we combine a
recently introduced algorithm for eigenvalue optimization [Mengi, 35, 2 (2014)] with
matrix-product states and operator based techniques that theoretically allows for the
detection of multipartite entanglement of hundreds of spins. To support the practical
importance of our scheme, we discuss states which are optimally detected and show
how they can be created in experiments with trapped ions. Generally, our approach
provides a scalable method to verify multipartite entanglement which may find a variety
of applications, e.g., as a benchmark of various experimental situations, ranging from
quantum simulators to adiabatic quantum optimization.
28
Exact Bethe ansatz spectrum of a tight-binding
chain with dephasing noise
Mariya Medvedyeva
Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
We construct an exact map between a tight-binding model on any bipartite lattice in
presence of dephasing noise and a Hubbard model with imaginary interaction strength.
In one dimension, the exact many-body Liouvillian spectrum can be obtained by application of the Bethe ansatz method. We find that both the non-equilibrium steady
state and the leading decay modes describing the relaxation at late times are related to
the eta-pairing symmetry of the Hubbard model. We show that there is a remarkable
relation between the time-evolution of an arbitrary k-point correlation function in the
dissipative system and k-particle states of the corresponding Hubbard model.
Probing the Dynamics of Superradiant Quantum
Phase Transition in a Single Trapped-Ion
Ricardo Puebla
Institute of Theoretical Physics, Ulm University, Germany
The Rabi model can undergo a superradiant quantum phase transition (QPT) despite
consisting of a single two-level system and a single bosonic mode [1]. Here we
demonstrate that the QPT and its critical dynamics near the QPT can be probed
in the setup of a single trapped ion, making use of equilibrium and non-equilibrium
universal functions of the Rabi model. We propose a scheme that can faithfully realize
the Rabi model in the extreme parameter regime to observe critical behavior: large
ratio of the effective atomic transition frequency to the oscillator frequency. It is
demonstrated that the predicted universal functions can indeed be observed based
on our scheme. Finally, the effects of realistic noise sources on probing the universal
functions in experiments are examined [2].
[1] M.-J. Hwang, R. Puebla, and M. B. Plenio, Phys. Ref. Lett. 115, 180404(2015).
[2] R. Puebla, M.-J. Hwang, J. Casanova, and M. B. Plenio, arxiv:1607.03781.
29
Topological Mechanics
Grazia Salerno
INO-CNR BEC Center, 38123 Povo (TN) Italy
We theoretically propose how to observe topological effects in a generic classical system
of coupled harmonic oscillators, whose oscillation frequency is modulated fast in time.
Making use of Floquet theory in the high-frequency limit, we identify a regime in which
the system is accurately described by a Harper-Hofstadter model where the synthetic
magnetic field can be externally tuned via the phase of the frequency modulation of the
different oscillators. We illustrate how the topologically protected chiral edge states, as
well as the Hofstadter butterfly of bulk bands, can be observed in the driven-dissipative
steady state under a monochromatic drive. In analogy with the integer quantum Hall
effect, we show how the topological Chern numbers of the bands can be extracted
from the mean transverse shift of the steady-state oscillation amplitude distribution.
Finally, we discuss the regime where the analogy with the Harper-Hofstadter model
breaks down.
30
Probing Relaxation at the Many-Body Localization
(MBL) Transition with Ultracold Fermions in Optical
Lattices
Sebastian Scherg
Quantum Optics Chair, Ludwig-Maximilians Universität München, Germany
The many-body localization transition is a dynamical phase transistion, which happens
over an extended range of energy densities.
The phase transistion seperates an ergodic, thermal phase, in which the eigenstate thermalization hypothesis (ETH) holds, from a non-thermal, localized phase, which violates
the ETH. We study this transistion using interacting Fermions in a one-dimensional
quasi-disordered optical lattice by monitoring the decay of an initially imprinted local
density pattern.
I will show recent experimental results on MBL focusing on the vicinity of the MBL critical point, where we find slow powerlaw dynamics, which might potentially be connected
to Griffith type effects. Furthermore, I will present recent experiments on periodical
driving of an MBL system, resulting in a localized phase at high drive frequencies and
an ergodic phase at low ones. Finally, I will explain recent preliminary data about MBL
in a 2D environment.
31
Nonthermal Fixed Points and Superfluid Turbulence
in Ultracold Bose Gases
Markus Karl, Christian-Marcel Schmied, Stefanie Czischek
Kirchhoff-Institute for Physics, Heidelberg University, Germany
Ultracold quantum gases provide various means to probe universal many-body dynamics
far from equilibrium. Here, we focus on the non-linear dynamical evolution induced
in an ultra cold Bose gas by a sudden initial parameter quench. Considering oneor multi-component (spin) systems, various types of spatial and wavenumber- space
patterns emerge, being characterized by universal scaling functions associated with
non-thermal fixed points. Such fixed points can be observed in existing experiments
and are closely related to quantum turbulence usually discussed in systems of more
than one spatial dimension. While these situations are associated with quenches to
a symmetry-broken state, quenches within the symmetric phase offer a way to probe
the properties of universal dynamics similar to those near a quantum critical point in
equilibrium. Scaling properties have been found which indicate the importance of prethermalisation temperatures long before dephasing has occurred in the nearly gapless
system. We discuss the theoretical results in the light of and illustrated by recent
experimental measurements.
32
Heteronuclear Efimov scenario in an ultracold
Bose-Fermi mixture with large mass imbalance
Juris Ulmanis
Physics Institute, Heidelberg University, Germany
Universality in few-body systems is a prominent topic in fundamental quantum physics.
One of its hallmarks is the Efimov effect, where pairwise resonantly interacting particles
can form an infinite geometric series of weakly-bound three-body states, the Efimov
states, following a discrete scaling law. Due to the large mass imbalance, an ultracold
Bose-Fermi mixture of Cs and Li atoms features a drastically reduced scaling factor,
making it a prototypical system for the thorough investigation of the heteronuclear
Efimov effect. Here we present our recent measurements and analysis of three-body
recombination spectra of Li+Cs+Cs collisions close to two broad Li-Cs Feshbach resonances. We observe how the heteronuclear Efimov scenario is critically modified by
the sign of the Cs-Cs intraspecies interaction and compare our results with universal
zero-range and van der Waals theories. Our findings show that the three-body parameter and the scaling factor between consecutive resonances are controlled not only by
the van der Waals forces, but also by the scattering length between the two bosons,
independent of short-range physics.
New Geometries for Ultracold Atoms in Optical
Lattices
Konrad Viebahn
Cavendish Laboratory, University of Cambridge, United Kingdom
We will present the latest developments on our new apparatus involving ultracold potassium and rubidium atoms in novel optical lattice geometries.
33
Role of geometry in nonlocal superfluids
Kali Wilson
Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh,
United Kingdom
In this work we perform numerical and experimental studies that demonstrate the key
role of fluid geometry when the fluid is also nonlocal. We show that the Bogoliubov
dispersion relation associated with elementary excitations in a nonlocal quantum fluid
may be modified by the system geometry, such that the system can be pushed into
a regime where superfluid behavior is observed despite a high degree of nonlocality.
This interplay between geometry and nonlocality is a general feature of the nonlocal
interaction, with applications to dipolar BECs and nonlocal photon fluids. Tailoring
the system geometry thus provides external control of the effective nonlocal length
characterizing the fluid, and sets a threshold wavevector below which a linear, sonic
dispersion relation consistent with superfluidity may be observed. We discuss this interplay in the context of recent experimental observations of superfluid behavior in a
room-temperature, nonlocal photon fluid in a propagating geometry. We have experimentally observed signatures of superfluid behavior in the dispersion relation, and in
the nucleation of vortex cores as the photon fluid flows past an extended obstacle,
despite working with a highly-nonlocal thermal nonlinearity expected to suppress such
superfluid behavior.
34
Participants
• L. Angenoorth (Universität Heidelberg,
Germany)
• K. Geier
Germany)
• A. Amo (Centre for Nanosciences and
Nanotechnologies (C2N), France)
• P. Hauke (University of Innsbruck,
Austria)
• K. Baumann (Goethe
Frankfurt, Germany)
• M. Holten
Germany)
Universität
(Universität
(Universität
Heidelberg,
Heidelberg,
• A. Bergschneider (Universität Heidelberg,
Germany)
• F. Jendrzejewski (Universität Heidelberg,
Germany)
• S. Butera (Heriot-Watt University
Edinburgh, United Kingdom)
• P. Jurcevic (University of Innsbruck,
Austria)
• I. Carusotto (BEC Trento, Italy)
• M. Karl
Germany)
• J.-S. Caux (University of Amsterdam,
The Netherlands)
• C. Ciuti (Univ. Paris Diderot, France)
• L. Cugliandolo (Université Pierre et
Marie Curie, France)
• S. Czischek (Universität Heidelberg,
Germany)
• A. Daley (University of Strathclyde,
United Kingdom)
• E. Demler (Harvard University, USA)
• M. F. Di Liberto (INO-CNR BEC Center
Trento, Italy)
• J. Eisert
Germany)
(Freie
Universität
Berlin,
(Universität
Heidelberg,
• M. Kastner (Stellenbosch University,
South Africa)
• P. Kunkel
Germany)
(Universität
Heidelberg,
• A. Lamacraft (University of Cambridge,
United Kingdom)
• D. Linnemann (Universität Heidelberg,
Germany)
• H. Lüschen (MPQ/LMU, Germany)
• O. Marty (Universität Ulm, Germany)
• M. Medvedyeva (University of Ljubljana,
Slovenia)
• S. Nascimbène (LKB ENS Paris, France)
• T. Enss
Germany)
(Universität
Heidelberg,
• N. Navon (University of Cambridge,
United Kingdom)
• S.
Erne
Germany)
(Heidelberg
University,
• M. Oberthaler (Universität Heidelberg,
Germany)
• F. Essler (University of Oxford, United
Kingdom)
• T.
Osborne
(Leibniz
Hannover, Germany)
• T. Gasenzer (Universität Heidelberg,
Germany)
• T. Ozawa (INO-CNR BEC Center and
University of Trento, Italy)
35
Universität
• T. Prosen (University of Ljubljana,
Slovenia)
• M. Prüfer
Germany)
(Universität
Heidelberg,
• T. Schweigler (TU Wien, Austria)
• A. Signoles (Universität Heidelberg,
Germany)
• R. Puebla (Ulm University, Germany)
• H. Strobel
Germany)
• M. Rabel
Germany)
Heidelberg,
• A. Tarkhov (Skolkovo Institute of Science
and Technology, Russia)
• G. Salerno (INO-CNR BEC Center, Italy)
• L. Todorov (Durham University, United
Kingdom)
(Universität
• A. Salzinger (Universität Heidelberg,
Germany)
• S.
Scherg
(Ludwigs-Maximilians
Universität München, Germany)
• C.-M. Schmied (Heidelberg University,
Germany)
• J. Schmiedmayer (TU Wien, Austria)
• U. Schneider (University of Cambridge,
United Kingdom / Ludwigs-Maximilians
Universität München, Germany)
36
• J. Ulmanis
Germany)
(Universität
(Heidelberg
Heidelberg,
University,
• K. Viebahn (University of Cambridge,
United Kingdom)
• M. Weitz (Universität Bonn, Germany)
• K. Wilson (Heriot-Watt
United Kingdom)
University,
• M. Wouters (Universiteit Antwerpen,
Belgium)
Committees
Scientific board
• Alberto Amo (Marcoussis)
• Jürgen Berges (Heidelberg)
• Jacqueline Bloch (Marcoussis)
• Iacopo Carusotto (Trento)
• Jens Eisert (Berlin)
• Thomas Gasenzer (Heidelberg)
• Markus Oberthaler (Heidelberg)
• Jörg Schmiedmayer (Vienna)
• Ulrich Schneider (Cambridge/Munich)
Coordinator
• Thomas Gasenzer (Kirchhoff-Institut für Physik, Universität Heidelberg)
Contact
Conference Assistant
Christiane Jäger
Universität Heidelberg
Synthetic Quantum Systems
Kirchhoff-Institut für Physik
Im Neuenheimer Feld 227
69120 Heidelberg
Germany
tel: +49 6221 54 5172
fax: +49 6221 54 5179
e-mail: [email protected]
www: http://www.kip.uni-heidelberg.de/matterwaveoptics/
37
Index
Programme
3
Practical Information
Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
7
7
Talks
Martin Weitz . . . .
Philipp Hauke . . .
Fabian Essler . . . .
Jean-Sébastien Caux
Petar Jurcevic . . .
Andrew Daley . . .
Leticia Cugliandolo .
Cristiano Ciuti . . .
Michiel Wouters . .
Tomaž Prosen . . .
Tomoki Ozawa . . .
Alberto Amo . . . .
Sylvain Nascimbène
Jens Eisert . . . . .
Austen Lamacraft .
Henrik Lüschen . .
Nir Navon . . . . .
Markus Karl . . . .
Thomas Schweigler
Adrien Signoles . . .
Eugene Demler . . .
Tobias Osborne . .
Iacopo Carusotto . .
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Posters
Andrea Bergschneider .
Salvatore Butera . . . .
Marco Fedele Di Liberto
Sebastian Erne . . . . .
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Oliver Marty . . . . . . .
Ricardo Puebla . . . . . .
Grazia Salerno . . . . . .
Sebastian Scherg . . . . .
Christian-Marcel Schmied
Juris Ulmanis . . . . . . .
Konrad Viebahn . . . . .
Kali Wilson . . . . . . . .
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28
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32
33
Participants
34
Committees
36
39
Internet
There is a wifi Internet access in the conference hall. Connect to WLAN ’UNIWEBACCESS’ and open your browser. It will automatically redirect to the login
page.
login: iq3
password: 8x7du
The web-page of the conference is:
http://www.thphys.uni-heidelberg.de/ smp/RETUNE2012/index.php
It contains additional information about the conference. We will try to assemble
the material of the conference and make it available on the web-page as well.
8