Download Quantum optics with GeV color center in diamond

Quantum optics with GeV color center in diamond
Alexey Akimova,b,c, Jingwei Fana, Ivan Cojocarua,c, Abdulrahman Alajlana, Xiaohan Liua
a
Texas A&M University, TX, USA
b
P.N. Lebedev Institute
c
Russian Quantum Center
* Corresponding author: [email protected]
Color centers in diamond attract a lot of attention due to unique properties of diamond, such its optical and
chemical purity, low concertation of nuclear spins in diamond matrix and also its physical and chemical
inertness [1]. Nitrogen vacancy (NV) color centers in diamond is the most studied color center in diamond
because its fluorescence rate does depend on spin state this way enabling readout of the spin state. This property
opens a lot of opportunities to for it implementation in quantum information processing [2] and sensing [3]
applications. Nevertheless, NV color center has number of important disadvantages, such as broad emission
spectrum dominated by phonons sideband with only 5% emission in zero-phonon sideband. Another problem is
its high sensitivity to surface and structural defects in diamond often introduced by surrounding nanostructures.
This disadvantages stimulated search for other color centers, which would have narrow spectrum dominated by
zero-phonon line and better behavior in nanostructures. First, SiV center was suggested as such a center. Due to
high symmetry of this center, it does not have dipole moment in the ground state and therefore is not as sensitive
to various surface defects and damages as NV center. Moreover, it happens to have narrow zero-phonon line
dominating the spectrum. However, unfortunately, exited state decay of this center is dominated by non-radiative
relaxation. The next natural candidate is GeV center since Ge is right under Si in the Mendeleev table. This
center is yet not well studied, but may be very promising candidate for development of quantum information
processing with it.
In this talk, I will present our resent results on manipulation of ensembles of GeV centers towards
developing quantum memory with it. In addition, I will present our results on possible implementation of GeV
center ensembles for temperature measurements.
Figure 1 A) GeV energy diagram, B) GeV room temperature spectra, C) EIT in ensemble of GeV centers at 4K.
References
[1]
V. N. Mochalin, O. Shenderova, D. Ho, and Y. Gogotsi, Nat. Nanotechnol. 7, (2011).
[2]
M. W. Doherty, N. B. Manson, P. Delaney, F. Jelezko, J. Wrachtrup, and L. C. L. Hollenberg, Phys. Rep.
528, 1 (2013).
[3]
R. Schirhagl, K. Chang, M. Loretz, and C. L. Degen, Annu. Rev. Phys. Chem. 65, 83 (2014).
THz Spectrometers based on ultrafast lasers Vasilis Apostolopoulos Physics and Astronomy, University of Southampton, Southampton, SO171BJ, UK [email protected] In the Terahertz (THz) laboratories group in the University of Southampton we work on developing novel THz emitters and spectrometers based on the concept of THz time domain spectrometry. I will present THz emitters based on diffusion currents where terahertz radiation can be generated by ultrafast photo‐excitation of carriers in a semiconductor. I will present 2D simulations of the THz generation effect taking into account the diffusion of carriers and the electric field using finite differences time domain simulations. Multiplexed emitter geometries will also be shown such as double‐metallic multiple emitters which operate under uniform illumination and are fabricated with periodic Au and Pb structures on GaAs. Terahertz emission in this case originates from diffusion currents and from the different Schottky barrier heights of the chosen metallic pair. I will demonstrate how our large area multiplexed emitters can be used in order to achieve THz focusing. Finally, I will present our work on the development of Mode‐locked Vertical External‐
Cavity Surface‐Emitting Lasers (ML‐VECSELs) that have seen advances in pulse energy and peak power thanks to improved power handling techniques and structure designs. The significant increase in gain and intra‐cavity power, coupled with the VECSEL’s accessible external‐cavity, has made the addition of intra‐cavity elements for frequency conversion possible even for lossy conversion mechanisms. I will show a gold‐patterned Semiconductor Saturable Absorbing Mirror (SESAM) that functions both as a slow saturable absorber in a ML‐VECSEL and as an intracavity strip line Photo‐Conductive Antenna (PCA) for THz emission. I will describe the design of the strip emitter, and how it performed on a THz‐Time Domain Spectrometer based on a ML‐Yb fibre laser. I will also show the characterisation of the ML‐VECSEL built with the patterned SESAM. Our target is to produce a laser which will perform intra‐cavity generation of THz and be the basis for a compact and fast spectrometer. Progress in GaN‐based quantum dots for single photon emission
Yasuhiko Arakawa1,2, Munetaka Arita,1 and Mark J. Holmes1,2
1
Institute for Nano Quantum Information Electronics, The University of Tokyo, Tokyo, Japan
2
Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
III-Nitride quantum dots, with their large band offsets and wide range of bandgaps, are
promising nanostructures for room temperature quantum information technologies, since
excitons can be sustained at higher temperature. Growth of high-quality GaN/AlN quantum
dots was achieved in 2002 by Metal Organic Chemical Vapour Deposition (MOCVD) with
Stanski-Krastnanov growth mode[1]. The quantum dots exhibited a large biexciton bindingenergy and a strong phonon interaction, leading to a single photon emission at 200 K in 2006
[2]. However, the magnitude of the binding energy of biexciton was not large enough to
realize single photon emission at room temperature.
A single photon emission at or above room temperature has been achieved using a
position controlled GaN/AlGaN nanowire quantum dot. The structure was grown by selective
area MOCVD and consists of GaN/Al0.8Ga0.2N core-shell type nanowires with a GaN
quantum dot inclusion near the tips. The quantum dots themselves typically have a lateral
dimension of ⊁10 nm and a vertical dimension of ⊁1 nm[3]. A large binding energy of
biexciton (> 60meV) in the quantum dot enabled single photon emissions at room temperature
in 2014 and at 350 K (77Ⅲ) in 2016, respectively[4,5].
We also succeeded in the formation of interface-fluctuation GaN quantum dots in a thin
GaN/AlxGa1-xN (x < 0.25) quantum well grown on a sapphire (0001) substrate. The high
temperature growth process led to a striking suppression of spectral diffusion and narrow
emission linewidths as low as ~90 μeV. A high purity single photon emission from this
interface fluctuation quantum dot was achieved and resulted in a measured raw g(2)(0) value
smaller than 0.1 at 10 K. This value is the lowest ever reported for a III-nitride quantum dots,
showing the remarkable nature of these quantum dots[6].
References
[1] M Miyamura, K Tachibana, and Y Arakawa, Appl. Phys. Lett. 80, 3937 (2002).
[2] S. Kako, C. Santori, K. Hoshino, S. Gotzinger, Y. Yamamoto, and Y. Arakawa, Nat.
Mater. 5, 887 (2006).
[3] K. Choi, M. Arita, S. Kako, Y. Arakawa et al., J. Cryst. Growth 370 328 (2013).
[4] M. Holmes, K Choi, S. Kako, M. Arita, and Y. Arakawa, NanoLett., 14 982 (2014).
[5] M. Holmes, K Choi, S. Kako, M. Arita, and Y. Arakawa, ACS Photonics 3 543 (2016).
[6] M. Arita, K. Choi, S. Kako, and Y. Arakawa, NanoLett., in press (2017).
Terahertz laser field effect on concentric double quantum rings
H.M. Baghramyana,*, M.G. Barseghyanb, A.A. Kirakosyanb, J. H. Ojedaa,c, D. Larozea
a
Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
Department of Solid State Physics, Yerevan State University, Alex Manoogian 1, 0025 Yerevan, Armenia
c
Grupo de Física de Materiales, Universidad Pedagógica y Tecnológica de Colombia, Tunja, Colombia
b
* Corresponding author: [email protected]
The influence of an intense terahertz laser field on one-electron energy spectrum and
intraband absorption is studied in two-dimensional GaAs/Ga0.7Al0.3As concentric double
quantum rings (QR) [1]. The wave function engineering in QRs is investigated in deep as
well.
Fig. 1. - Energy dependence on laser field parameter α0. Wave functions for the smallest α0 = 0 and biggest α0
= 3nm values are shown as well. R1in, R1out are inner and outer radii of inner ring and R2in, and R2out are
respectively those of the outer one.
Fig. 1 shows that the increment of α0 modifies the initial (in the absence of laser field)
degeneracy. For example, the 3rd state now becomes degenerated with the ground state, but
initially the latter was not degenerated at all. There are also 2nd with 7th, 4th with 5th, 6th with
9th states that form degenerated pairs. We find the results of the current work useful for the
characterization of quantum ring based devices, such as THz photodetectors [2].
References
[1] V. M. Fomin, Physics of Quantum Rings, NanoScience and Technology (Springer-Verlag Berlin Heidelberg,
2014).
[2] S. Bhowmick et al. Appl. Phys. Lett. 96, 231103 (2010).
Realistic modeling of quantum-dot heterostructures: theory and applications
Daniele Barettina,b*
UNICUSANO, Università degli Studi Niccolò Cusano-Telematica Rome, Italy.
b
Department of Electronic Engineering, University of Rome “Tor Vergata” Via del Politecnico 1, 00133, Rome,
Italy
a
* Corresponding author: [email protected]
Different numerical simulations of quantum-dot heterostructures derived from experimental results are
presented. Three-dimensional models have been extrapolated directly by atomic force microscopy and
high-resolution transmission electron microscopy results, and electromechanical, continuum
, atomistic Tight Binding and optical calculations are showed and compared with benchmark
calculations with ideal structures applied in the literature [1, 2]. According these results, the use of
more realistic structures can provide significant improvements into the modeling and the
understanding of quantum-dot nanostructures.
Fig. 1: Top: a two-dimensional image of the out-of-plane strain obtained by geometric phase analysis of the
HRTEM image used to derive the three-dimensional structure. Bottom: the three-dimensional extrapolated active
region structure.
As a possible application of a realistic multi-scale approach is the study of Indium Gallium Nitride
systems for their increasing role in the fabrication of LEDs, since by In content engineering in the
active region it is theoretically possible to cover the whole visible spectrum range [3].
References
[1] D. Barettin et al, Nanotechnology, 25 (19) (2014).
[2] D. Barettin et al, Journal of Applied Physics, 117 (2015)
[3] D. Barettin et al, Nanotechnology, 28 (1) (2017).
Carbon-based Perovskite Solar Cells
Jessica Barichello1,2, Fabio Matteocci1, Enrico Lamanna1, Alessandro Palma1, Aldo Di
Carlo1
1
CHOSE – Centre for Hybrid and Organic Solar Energy – University of Rome ‘‘Tor
Vergata’’, via del Politecnico 1, 00133 Roma, Italy
2
Department of Environmental Sciences, Informatics and Statistics, Ca' Foscari
University of Venice, Via Torino 155, 30107 Mestre (VE) Italy
Corresponding author: [email protected]
In the last 5 years, the photovoltaic community has been attracted from a new
technology, Organometal trihalide Perovskite Solar Cells (PSCs), due to the great
increasement of the Power Conversion Efficiency (PCE) that started from a 13% and
now is a certified 22,6 %. This recent result is approaching to that one of mono-crystal
silicon solar cells and made us believe that PSCs can be a real competitor of the old PV
technologies. Before entering in the PV market, some changes have to be done in order
to solve toxicity and stability problems. The structure that obtained the best efficiency
so far needs the application of gold and spiro-OMeOTAD as electrode and hole
transport materials (HTM), respectively, but this limits their widespread use due to the
high cost of these materials and their environmental impact. These issues may be
overcome with Carbon based PSCs (C-PSC), where both Au electrode and HTM are
replaced by a carbon coating layer since carbon materials are stable, water resistant and
inert to ionic migration. In this research, an optimization study of the C-PSC structure
and of the perovskite growth has been performed: the Al2O3 layer, behaving as
insulator, substituted the conventional ZrO2 layer [1] and the addition of water, before
creating the perovskite, helped to have a better pore-filling and more perovskite’s
nucleation sites. In order to scale-up to large device area the screen printer technique for
the TiO2 and Al2O3 deposition was utilized and the two-step deposition method for the
growth of perovskite’s crystals has been employed. Tests with Transfer Length Method
were conducted with the aim to estimate the contact area to produce a C-PSCs module.
A maximum PCE of 12.3 % was achieved with a fully-printable TiO2-Al2O3-Carbon
structure and initial attempts to scale the process to large area automated deposition
showed a PCE of 7.71 % on 1 cm2 with large room for improvements. Stability tests
already showed promising results for a no-sealed sample during a 50 days shelf life.
Reference
[1] H. Chen, S. Yang. Adv. Mater. 2017, 1603994
Plasmonic, all-dielectric and hybrid nanoantennas:
fabrication, reconfiguration and optical properties
Pavel Belov*
ITMO University, Kronverkskiy pr., 49, St. Petersburg, 197101
* Corresponding author: [email protected]
The resonant metallic nanoparticles are proven to be efficient systems for the electromagnetic field control
at nanoscale, owing to the ability to localize and enhance the optical field via excitation of strong plasmon
resonances. In turn, high index dielectric nanoparticles with low dissipative losses in the visible range,
possessing magnetic and electric Mie-type resonances, offer great opportunity for light control via designing of
scattering properties [1]. Recently, the combination of these two paradigms in the form of metal-dielectric
(hybrid) nanostructures (nanoantennas and metasurfaces) has allowed utilizing the advantages of both
plasmonics and all-dielectric nanophotonics.
We present our recent results on femtosecond laser-assisted above mentioned nanostructures fabrication and
manipulation by their optical properties. In particular, we developed novel methods for plasmonic [2],
all-dielectric [3], and hybrid [4] nanostructures. Also, we proposed a novel concept for ultrafast manipulation by
scattering properties of an individual all-dielectric nanoantenna by means of generation of electron-hole plasma
[5].
For the first time to our knowledge, we present the experimental evidence of near-field enhancement of the
magnetic fields with silicon resonant nanodimers at visible frequencies. The response of the system has been
studied as a function of wavelength, polarization, and gap. The NSOM measurements show a very good
correlation with the simulations. When the simulated near-fields are broken down into their components, it is
confirmed that the resonance measured in the near-field is strongly magnetic in nature, for both polarizations [6].
For a single Si nanoparticle, we have studied experimentally both magnetic and electric optically-induced
resonances by combining polarization-resolved dark-field spectroscopy and near-field scanning optical
microscopy (NSOM) measurements. We reveal that the scattering spectra exhibit strong sensitivity of electric
dipole response to the probing beam polarization, and attribute the characteristic asymmetry of measured NSOM
patterns to the excitation of a magnetic dipole mode. The proposed experimental approach can serve as a
powerful tool for the study of photonic nanostructures possessing both electric and magnetic optical responses
[7]. We also reveal remarkable substrate-driven transformations of electric and magnetic dipole resonances of a
silicon nanoparticle on metal, manifesting as the modification of Q-factor of the resonances followed by strong
enhancement of the respective fields [8].
We experimentally observe a new type of optical surface waves in resonant hyperbolic metasurface. We
reveal a topological transition from elliptic to hyperbolic regime for TM-plasmons and predict self-collimating
quasi-one-dimensional propagation of surface waves.
Finally, we demonstrate in the experiment resonant subwavelength topological edge states supported by
zigzag arrays of nanoparticles. Using direct near-field measurements, we observe polarization-controlled
switching of the edge states and enhancement of photonic spin Hall effect [9-11].
References
[1] A Krasnok et al., SPIE Optics&Optoelectronics, 950203-950203-17 (2015).
[2] S.V. Makarov, et al., Laser&Photonics Reviews (2015) (Accepted).
[3] P.A. Dmitriev, et al, Nanoscale (2015) (Accepted).
[4] D.A. Zuev, et al., Advanced Materials (2015) (Accepted).
[5] S Makarov, et al., Nano Letters 15, 9, 6187-6192 (2015).
[6] R.M. Bakker, et al. Nano Letters 15, 3, 2137-2142 (2015).
[7] D. Permyakov, et al., Applied Physics Letters, 106, 171110 (2015).
[8] I.S. Sinev, et al., Laser & Photonics Reviews, 10(5), 799-806 (2016).
[9] I.S. Sinev, et. al.,. Nanoscale, 7(28), 11904-11908 (2015).
Exotic states of matter with polariton graphs
Natalia G. Berloff 1,2 and Pavlos G. Lagoudakis 1,3
Skolkovo Institute of Science and Technology, Russian Federation
Dept of Applied Mathematics and Theoretical Physics, University of Cambridge, UK
3
Dept of Physics and Astronomy, University of Southampton, UK
1
2
Frustrated spin systems represent one of the most demanding problems of condensed matter physics [1]. A large variety of computationally intractable systems can be mapped
into certain universal classical spin models such as an Ising, XY or Heisenberg models,
that are characterised by the given degrees of freedom, ”spins”, by their interactions,
”couplings,” and by the associated cost function, ”Hamiltonian”. Various physical platforms have been proposed to simulate such models using superconducting qubits, optical
lattices, coupled lasers etc. We proposed polariton graphs as a new platform for finding
the global minimum of classical XY Hamiltonians in a variety of geometries and coupling
strengths [2]. Geometric frustration leads to a rich variety of possible spin configurations
in the ground and excited states of these systems due to the competition between interactions, geometry, nonlinearity of the spin lattice with a potential of creating novel, exotic
phases. We show that the low energy states of polaritonic graphs demonstrate various
classical regimes: ferromagnetic, antiferromagnetic and frustrated spiral phases, at the
same time nonlinear interactions at higher pumping intensities bring about novel exotic
phases that can be associated with spin liquids [3].
References
[1] Sachdev, S. Quantum magnetism and criticality, Nat. Phys. 4, 173 (2008).
[2] Berloff, N.G et al. Realizing the classical XY Hamiltonian with polariton graphs.
arXiv:1607.06065 (2016)
[3] Kalinin K. et al. Exotic spin phases with polariton chains. In review by PRL
(2017).
Lattices of Quantized vortices in polariton superfluids
Alberto Bramatia,*
a
Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, ENS, Collège de France, Paris, France
* Corresponding author: [email protected]
Microcavity polaritons, the half-light-half-matter particles arising from the strong coupling between excitons
and photons, behave like weakly interacting composite bosons. Due to their excitonic part they exhibit
non-linear interaction while their photonic part allows creating and detecting them optically. In this sense the
polaritons are part of a wider family of systems where an effective photon-photon interaction can be engineered,
resulting in a hydrodynamical-like behavior. Such systems are labeled as quantum fluids of light [1]. These
ingredients make polariton systems a unique platform to study quantum fluid effects in a semiconductor chip and
to evidence properties very difficult to access in other systems.
In this talk I will focus on the description of the recent studies conducted in our group, in the quest for the
observation of lattices of quantized vortices in polariton superfluids. In particular I will show how the
implementation of optical traps for polaritons allows for the realization of vortex-antivortex lattices in confined
geometries and how the development of flexible all-optical methods to inject a controlled orbital angular
momentum (OAM) in such systems results in the observation of patterns of same sign vortices [2, 3]. These
results constitute a significant step forward in our understanding of the quantum fluids of light and open the way
to the study of Abrikosov-like physics and new vortex collective phenomena in these systems.
Fig. 1 Chain of vortices in a polariton superfluid
References
[1] I. Carusotto and C. Ciuti, Quantum Fluids of Light, Rev. Mod. Phys. 85, 299 (2013).
[2] T. Boulier, H. Terças, D. D. Solnyshkov, Q. Glorieux, E. Giacobino, G. Malpuech and A. Bramati, Vortex
chain in a resonantly pumped polariton superfluid, Scientific Reports 5, 9230 (2015).
[3] T. Boulier, E. Cancellieri, N.D. Sangouard, Q. Glorieux, A. V. Kavokin, E. Giacobino, A. Bramati, Injection
of orbital angular momentum and storage of vortices in polariton superfluids, Phys. Rev. Lett., 116, 116402
(2016).
Origin and mode structure of lasing emission from a single GaAs/GaNAs core/shell
nanowire
S. L. Chen,a M. Jansson,a J. E. Stehr,a Y. Huang,a F. Ishikawa,b W. M. Chen,b and I. A. Buyanovaa,*
*
a
Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden on
b
Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan
* Corresponding author: [email protected]
Semiconductor nanowires (NWs) are currently regarded among the most promising systems for constructing
nanolasers, as a nanowire represents a naturally formed cavity and also provides gain medium. The flexibility in
engineering the gain material and laser cavity can be extended by employing dilute nitride GaNAs alloys. The
giant bowing in the bandgap energy characteristic for dilute nitrides allows easy tuning of lasing wavelengths,
whereas an increase in electron effective masses upon N incorporation reduces carrier spill-out from GaNAs
quantum wells, improving laser thermal stability. Moreover, alloying with nitrogen improves the surface quality
of NWs, suppressing detrimental surface recombination [1].
In this work we demonstrate lasing from the GaNAs region of GaAs/GaNAs core/shell NWs grown by
molecular beam epitaxy. The 5K photoluminescence (PL) spectra measured at low pump fluences (Pexc) are
found to originate from localized exciton emission, coupled to the fundamental HE11a/b Fabry-Perot cavity modes.
With increasing the excitation power, sharp lasing emission was observed from the GaNAs band-to-band
transitions (see Fig.1), which exhibits an ‘S’-shape dependence on Pexc accompanied by line narrowing. By using
rate equation analysis, a threshold gain, gth, of 3300 cm-1 and a spontaneous emission coupling factor, β, of 0.045
are derived. The performed finite difference time domain (FDTD) simulation identify the HE21b cavity mode as
the lowest threshold mode for lasing. This conclusion is supported by the observed predominant polarization of
the lasing line along the NW axis, in agreement with the expected far-field polarization profile of the HE21b mode.
Furthermore, the lasing emission from the nanowires can sustain up to ~ 150 K, even without intentional
passivation of the GaNAs surface. Our work [2], therefore, underlines the potential of GaNAs alloys as an active
gain media and represents the first step towards the room temperature-operating GaNAs-based NW lasers.
Fig.1. Power dependent PL spectra at 5 K.
References
[1] S. L. Chen, W. M. Chen, F. Ishikawa, and I. A. Buyanova, Sci. Rep. 5, 11653 (2015).
[2] S. L. Chen, M. Jansson, J. E. Stehr, Y. Huang, F. Ishikawa, W. M. Chen, and I. A. Buyanova, Nano Lett. DOI:
10.1021/acs.nanolett.6b05097 (2017).
Antibunched Light with Bragg-Cavity Polaritons: Dynamics and Optimization
a
Emiliano Cancellieria
Department of Physics and Astronomy, University of Sheffield, Sheffield, UK.
* Corresponding author: [email protected]
Bragg-Cavity polaritons are half-light half-matter quasiparticles that have been intensively studied in recent
years for their remarkable properties: ultrafast dynamics, strong nonlinearity, out-of-equilibrium nature, and
integrability in modern semiconductor-based technology. After the observation of several important effects such
as condensation, superfluidity, and vortex formation, a considerable attention has been recently focused on the
observation of quantum-mechanical signatures like, for example, the polariton blockade regime. In this context,
the theoretical proposal of non-conventional blockades [1,2], the observation of squeezed light [3], and the
injection of single polariton states [4] are probably the most remarkable results. However, the experimental
observation of antibuched light induced by polariton-polariton interactions is a cornerstone yet to be achieved.
In this work, first we demonstrate that the second order correlation function, at zero-time delay, of the light
emitted by a Bragg-cavity polariton system can evolve in time (i.e.
) only in the presence of
an external pump. This important result opens the way to the use of laser-pulse optimization for the generation
light with stronger antibunching, i.e. with lower values of
.
Secondly, starting from the observation that the generation of antibunched light from a coherent laser beam
is, essentially, an intensity-dependent filtering, we propose to use a cascade of two or more Bragg-cavity systems
to further increase the antibunching of the considered light beam. With this technique, using state-of-the-art
cavity parameters, we obtain an improvement of about 17-18% at each cascade step, and achieve single photon
emission (
) at the stage of four cavities. A specific advantage of this approach is that since the
better antibunching is achieved above the non-linear threshold for the last cavity in cascade (see Figure 1), the
intensity of the emitted light can be considerably high.
Fig. 1 Polariton population in the first (red) and second (green) cavities in cascade as a function of the pump
intensity. For this set of simulations, the cavity linewidths are set to be
meV and the polariton-polariton
interactions
meV. Above the second threshold the light emitted from the two cavities has
and
respectively.
References
[1] T. C. H. Liew and V. Savona, Phys. Rev. Lett. 104, 183601 (2010).
[2] M. Bamba, M., A. Imamŏglu, I. Carusotto and C. Ciuti, Phys. Rev. A 83, 021802 (2011).
[3] T. Boulier, et al., Nature Communications 5, 3260 (2014).
[4] A. Cuevas et al., arXiv:1609.01244 (2016).
Tunable single photon source with carbon nanotube
Yannick Chassagneuxa *, Adrien Jeanteta, Theo Claudea, Jakob Reichelb, Christophe Voisina
Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS, Université Pierre et Marie Curie,
Université Paris Diderot, 24 rue Lhomond, 75005 Paris, France
b
Laboratoire Kastler Brossel, Ecole Normale Supérieure, CNRS, Université Pierre et Marie Curie,
24 rue Lhomond, 75005 Paris, France
a
* : [email protected]
Carbon nanotubes have emerged as original nano-emitters for future single-photon sources in the telecom
wavelengths [1]. Coupling the nanotube to a micro-cavity brings a invaluable handle to control single-photon
emission, regarding the rate, the yield, the directionality and the extraction. All those features are related to the
so-called Purcell effect that results from the interaction of a quasi-two-level system with a high Q and low modevolume cavity. Due to the 1D geometry of carbon nanotubes, the coupling to the phonon bath is strongly
enhanced resulting in the well-known phonon wings [2]. This additional degree of freedom brings a very rich
physics that can be exploited to enlarge the bandwidth of the source in view of multiplexing. A consequence of
the non-Markovian decoherence induced by the phonon bath is the asymmetry between the phonon-assisted
absorption and emission processes. Using those transitions in the Purcell regime can lead to an enhanced singlephoton efficiency above the standard limit imposed by the emitter and cavity intrinsic losses. We developed a
widely tunable cavity technique, based on laser-engineered optical fibers to investigate this effect. We measure
the single-photon emission properties both in cw and time-resolved and explain the strong asymmetry of the
efficiency with respect to the detuning.
Figure
Fig. 1: (a) 2D plot of the emission spectrum of a carbon nanotube
References
[1] A. Jeantet et al., Phys. Rev. Lett. 116, 247402 (2016) , X. Ma, et al., Nat. Mat. 10, 671 (2015).
[2] F. Vialla et al., Phys. Rev. Lett. 113, 057402 (2013)
Spin-dependent processes in polymer-fullerene solar cells
Y. Puttisong, F. Gao, Y. Xia, I. A. Buyanova, O. Inganäs and W. M. Chen
Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping,
Sweden
* Corresponding author: [email protected]
Efficient solar energy conversion in bulk hetero-junction (BHJ) organic photo-voltaic
devices relies on photo-generation of charges at the donor and accepter hetero-interfaces. An
important requirement in further improving device efficiency is our understanding of the
photo physics of interfacial charge transfer (CT) states - the precursors for charge generation,
and their contributions to both charge generation and energy losses. Earlier studies have
shown that spin and localization of the interfacial CT states play crucial roles in ultrafast
charge generation and the subsequent recombination loss in polymer/fullerene blend systems.
However, a direct proof for such roles on the microscopic level is still lacking.
In this work, we focus on the direct probing of the optically-excited lowest CT exciton
states (CT1) and their associated spin-dependent processes in a model polymer/fullerene solar
cell based on TQ1/PCBM blends. By combining selective optical excitation and detection
with the optically detected magnetic resonance (ODMR) technique, we are able to identify the
triplet CT1 states and the associated spin-spin interaction. With this, we estimate the
electron-hole separation of the CT1 exciton to be about 1 nm, within the physical dimension
of a one-polymer-one-fullerene unit. The size of the CT1 exciton is found to be identical in the
blends regardless of the fullerene load and aggregation that are known to affect the degree of
delocalization of CT excited states. We therefore conclude that the exciton localization of the
CT1 state is not responsible for the observed different efficiency of the solar cells with
different fullerene loads. In addition, we also provide direct evidence that CT1 can mediate
charge loss by facilitating intersystem crossing between the singlet and triplet of CT1,
trapping and bimolecular recombination of separated charges via CT1, and electron back
transfer from CT1 to the polymer triplet. Interestingly, we also observe at the same time an
efficient charge generation via the CT1 state. As such, we purpose a dual role of CT1 in both
charge loss and charge generation. We furthermore suggest the physical principle and possible
pathways to turn CT1 from a loss channel into a charge generation channel.
Dissipative phase transitions in photonic lattice systems
Cristiano Ciuti,1,∗
Laboratoire Matériaux et Phénomènes Quantiques,
Université Paris Diderot et CNRS, 75013 Paris, France.
* [email protected]
1
The manybody physics of photons is the subject of fundamental theoretical studies and
experimental investigations in a wide variety of nonlinear optical platforms including semiconductor microcavities, superconducting quantum circuits and atomic Rydberg gases [1].
In the broader field of open manybody systems, a growing interest is emerging for dissipative phase transitions, i.e., critical phenomena affecting the manybody steady-state
(for the case of spin systems, see, e.g., Refs. [2-5]). In this invited talk, I will present the
results of recent studies revealing fundamental properties of dissipative phase transitions
in nonlinear optical resonators [6-9] and cavity lattices [10,11]. In particular, I will discuss:
(i) the dynamical properties associated to the critical slowing down and the closing of the
so-called Liouvillian spectral gap via dynamical optical hysteresis [6,7]; (ii) the subtle link
between the thermodynamical limit of infinite number of sites in a lattice and the limit of
large number of photons in a single cavity [9]; (iii) the finite-size scaling of the dynamical
properties [10] and role of dimensionality for a first-order phase transition obtained by
coherent quasi-resonant driving of a lattice of coupled Kerr cavities [10]; (iv) the phase
diagram of an incoherently pumped lattice in the regime of strongly interacting photons
[11]. Moreover, future perspectives will be discussed.
Acknowledgements: for the work presented in this talk, I would like to warmly thank
all the members of my group and the external collaborators, who are cited in the references below. Funding from ERC (via the project CORPHO No. 616233) is gratefully
acknowledged.
References
[1] I. Carusotto, C. Ciuti, Rev. Mod. Phys. 85 (1), 299-366 (2013).
[2] E. M. Kessler et al., PRA 86, 012116 (2012).
[3] T. E. Lee, S. Gopalakrishnan, and M. D. Lukin, PRL 110, 257204 (2013).
[4] J. Jin et al., PRX 6, 031011 (2016).
[5] R. Rota, F. Storme, N. Bartolo, R. Fazio, C. Ciuti, PRB 95 (13), 134431 (2017).
[6] W. Casteels, F. Storme, A. Le Boité, C. Ciuti, PRA 93, 033824 (2016).
[7] S.R.K. Rodriguez, W. Casteels, F. Storme, N. Carlon Zambon, I. Sagnes, L. Le Gratiet,
E. Galopin, A. Lemaitre, A. Amo, C. Ciuti, J. Bloch, PRL in press (arXiv:1608.00260)
and references therein.
[8] N. Bartolo, F. Minganti, W. Casteels, C. Ciuti, PRA 94, 033841 (2016).
[9] W. Casteels, R. Fazio, C. Ciuti, PRA 95 , 012128 (2017).
[10] F. Vicentini, F. Minganti, R. Rota, N. Bartolo, G. Orso, C. Ciuti, in preparation.
[11] A. Biella, F. Storme, J. Lebreuilly, D. Rossini, R. Fazio, I. Carusotto, C. Ciuti,
preprint arXiv:1704.08978.
"HYBRID LAYER AND OTHER STRUCTURES CONTAINING B, C, AND N”
Marvin L. Cohen
Department of Physics
University of California at Berkeley
and
Materials Sciences Division
Lawrence Berkeley National Laboratory
Berkeley, Ca 94720, USA
SUBJECTS CATEGORY: Hybrid structures and two-dimensional crystals
Abstract
This presentation will discuss recent progress in first-principles studies of the
structural and electronic properties of hybrid layer and other structures built from boron,
carbon, and nitrogen.
In parallel with experimental studies, first-principles calculations of hybrid layer
systems such as graphene/hexagonal boron nitride heterostructures have revealed the
interesting and potentially useful properties of these materials.
We will also describe the properties of possible all carbon and also boron-carbonnitrogen kagome lattices. These calculations use phonon dispersion curves to demonstrate
the thermodynamic stabilities of the kagome lattices. The B-C-N kagome lattices are
wide-band gap semiconductors having direct and indirect band gap transitions.
In addition, we will discuss how conjugated p-orbital interactions, common to
most carbon allotropes, can in principle produce a new type of topological band structure,
forming a so-called Weyl-like semimetal in the absence of large spin-orbit coupling.
THz meta-atom quantum well
photo-detectors with ultrafast response
R. Colombelli1, B. Paulillo1, S. Pirotta1, H. Nong2, P. Crozat1, S. Guilet1,
G. Xu1,3, S. Dhillon2, L. Li4, A.G. Davies4, E.H. Linfield4
1
Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, C2N – Orsay, 91405 Orsay cedex, France
2
Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS, Université Pierre et Marie Curie, Paris, France
3
Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
4
School of Electronic and Electrical Engineering, University of Leeds, Leeds, United Kingdom
Abstract
Terahertz (THz) and sub-THz frequency emitter-detector technology is receiving increasing
attention because of key applications in healthcare, process control and metrology. In
particular, semiconductor-based ultrafast THz receivers are desired for compact, ultrafast
spectroscopy and communication systems: quantum well infrared photodetectors (QWIP) are
excellent candidates given their intrinsic ps-range response [1]. Each particular application
poses specific requirements on the system components, but ultra-fast operation—for either
emission or detection—is usually a vital functionality (e.g. in wireless communications, or in
real-time imaging).
In this contribution, we devise and demonstrate meta-atom QWIP detectors with dimensions
below the diffraction limit, operating around 3 THz with ultra-fast response. The key idea is to
exploit a miniaturized RF antenna as a coupler element to efficiently feed THz radiation (λ=100200 µm) into a sub-wavelength (4 µm) QWIP active core. Photocurrent spectra have been
acquired and they show a relatively broad detection peak centred around 3 THz, spanning the
2-4 THz band.
The extremely small size leads to measured optical response speeds of up to ∼3 GHz, and an
expected device operation of up to tens of GHz, based on experimental measurement of the Sparameters. Both arrays of detectors and single-pixels have been implemented with this new
architecture, with the latter ones exhibiting ultra-low dark currents below the nA.
[1]
Schneider, H. (Harald) & Liu, H. C. Quantum well infrared photodetectors: physics and applications.
(Springer, 2007).
Localized Phonon Polaritons:
A Novel Platform for Mid-Infrared Quantum Polaritonics
Simone De Liberato
School of Physics and Astronomy, University of Southampton, Southampton,
SO17 1BJ, United Kingdom
Corresponding author: [email protected]
Optical phonons at the surface of a nanostructured polar crystals can hybridize with
light, creating mixed excitations called localized phonon polaritons. Those
interface-bound excitations are in many regards mid-infrared analogous of
localized plasmons supported by metallic resonators, but they absent themselves
from the Ohmic loss characteristic of plasmonic systems. Localized phonon
polaritons are developing into an innovative platform for mid-infrared quantum
polaritonics. This is due to their extremely small mode volumes, long lifetimes, and
large nonlinearities, as well as the relative facility to fabricate nanoresonators with
features at the 100nm scale.
In this talk I will give an overview of our investigations into this innovative
platform. I will start by reviewing localized phonon polaritons main features [1]
and introducing a microscopic quantum theory capable of capturing their peculiar
properties [2]. I will then present some recent advances we obtained in this field:
from the observation of strong coupling between localized and propagative modes
[3], to nonlinear polariton scattering [4,5].
Fig. 1: SEM image (left) of a SiC sample patterned by micropillars studied in Ref.
[3]. Experimental reflectance map (right), highlighting the strong coupling
(anticrossing) between the almost dispersionless localised phonon polaritons and
the dispersive substrate surface modes as a function of the pillar distance.
References
[1] C. R. Gubbin, S. A. Maier, and S. De Liberato, PRB 95, 035313 (2017)
[2] C. R. Gubbin, S. A. Maier, and S. De Liberato, PRB 94, 205301 (2016)
[3] C. R. Gubbin, et al., PRL 116, 246402 (2016)
[4] I. Razdolski, et al., Nano Lett. 16, 69546959 (2016)
[5] C. R. Gubbin and S. De Liberato, arXiv:1701.06729
Towards lattices of trapped exciton-polariton condensates
Yago del Valle-Inclan Redondo1, H. Ohadi*1, A. J. Ramsay2, H. Sigurdsson3, A. Dreismann1, Y. G. Rubo4, S. I.
Tsintzos5, Z. Hatzopoulos5, T. C. H. Liew6, I. A. Shelykh3,7, P. G. Savvidis5,8 and J. J. Baumberg1
1
Department of Physics, Cavendish Laboratory, University of Cambridge
2
Hitachi Cambridge Laboratory
3
Science Institute, University of Iceland
4
Instituto de Energías Renovables, Universidad Nacional Autónoma de México
5
FORTH, Institute of Electronic Structure and Laser, Heraklion
6
School of Physical and Mathematical Sciences, Nanyang Technological University
7
ITMO University, St. Petersburg
8
Department of Material Science and Technology, University of Crete
* Corresponding author: ho278 @cam.ac.uk
In the first part of my talk I will discuss the spin behavior of optically trapped exciton-polariton condensates
under non-resonant linearly polarised pumping, and the stochastic formation of left- or right-circularly polarized
condensates and its connection with nonlinear self-trapping [1]. I will briefly describe how we exploit this new
phenomenon to demonstrate a sub-femtojoule field-effect polariton spin switch [2].
In the second part of my talk, I will show how we can build on the single condensate case and find tunable
spin correlations between two neighbouring magnetized trapped condensates [3], and continue to show our latest
results controlling the behavior of larger arrays of condensates.
Fig. 1: Array of four condensates (orange light) created using a
square array of non-resonant (blue) laser beams
References
[1] H. Ohadi et al. Phys. Rev. X 5, 031002 (2015)
[2] A. Dreismann et al. Nature Mat. (2016)
[3] H. Ohadi et al. Phys. Rev. Lett. 116, 106403 (2016)
Short THz pulse generation from a dispersion compensated modelocked semiconductor
laser
Feihu Wang1, Hanond Nong1, Tobias Fobbe2, Valentino Pistore1, Sarah Houver1, Sergej Markmann2, Nathan
Jukam2, Maria Amanti3, Carlo Sirtori3, Souad Moumdji4, Raffaele Colombelli4, Lianhe Li5, Edmund Linfield5,
Giles Davies5, Juliette Mangeney1, Jérôme Tignon1, and Sukhdeep Dhillon1,*
1
Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et
Marie Curie-Sorbonne Universités, Université Paris Diderot, Sorbonne Paris Cité, 24 rue Lhomond, 75231
Paris Cedex 05, France
2
Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum,
Germany
3
Laboratoire Matériaux et Phénomènes Quantiques, Université Paris Diderot, Sorbonne Paris Cité, CNRS-UMR
7162, 75013 Paris, France
4
Institut d’Electronique Fondamentale, Université Paris-Sud, CNRS UMR 8622, 91405 Orsay, France
5
School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds
* Corresponding author: [email protected]
Dispersion compensation is vital for the generation of ultrashort and single cycle pulses from modelocked
lasers across the electromagnetic spectrum. It is typically based on addition of an extra dispersive element to the
laser cavity that introduces a chromatic dispersion opposite to that of the gain medium. To date, however, no such
scheme have been successfully applied to terahertz (THz) quantum cascade lasers (QCL) for short and stable pulse
generation in the THz range. In this work, we will summarize the current state-of-the art [1–3] and show a
monolithic on-chip compensation scheme (fig. a) for a modelocked QCL, permitting THz pulses to be considerably
shortened from 16ps to 4ps (fig. b). This is based on the realization of a small coupled cavity resonator that acts as
an ‘off resonance’ Gires-Tournois interferometer (GTI), permitting large THz spectral bandwidths to be
compensated. This novel application of a GTI opens up a direct and simple route to sub-picosecond and single
cycle pulses in the THz range from a compact semiconductor source.
(a)
(b)
Fig a) GTI schematic a) Schematic of the GTI coupled to a QCL to realised ultrashort THz pulses. The inset
represents the GTI with asymmetric reflectivities, r1 and r2 and a cavity length, l. b) Short Pulse generation from
THz QCLs. Comparison of a QCL with a GTI (red) and a standard QCL cavity (black).
References
[1] D. Bachmann, M. Rösch, M. J. Süess, M. Beck, K. Unterrainer, J. Darmo, J. Faist, and G. Scalari, Optica 3,
1087 (2016).
[2] F. Wang, K. Maussang, S. Moumdji, R. Colombelli, J. R. Freeman, I. Kundu, L. Li, E. H. Linfield, A. G.
Davies, J. Mangeney, J. Tignon, and S. S. Dhillon, Optica 2, 944 (2015).
[3] S. Barbieri, M. Ravaro, P. Gellie, G. Santarelli, C. Manquest, C. Sirtori, S. P. Khanna, E. H. Linfield, and A.
G. Davies, Nat. Photonics 5, 306 (2011).
Graphene Interface Engineering for Perovskite Solar Cells.
Aldo Di Carloa*, A. Agresti, S. Pescetelli, B. Taheri, A. L. Palma
a
Centre for Hybrid and Organic Solar Energy, University of Rome Tor Vergata, Rome (Italy)
* Corresponding author: [email protected]
Hybrid organic/inorganic Perovskite materials are revolutionizing the field of solution-processed
optoelectronics. In particular, III-generation photovoltaics was boosted by the advent of Perovskite Solar Cells
(PSC). In this contests, recent studies demonstrated that interface between layers forming PSC are crucial for the
control of efficiency and stability of the cell. In fact, processes occurring at the interface such as recombination,
charge transfer, intermixing and ionic diffusion rule the performance and the stability of the solar cell. Owing to
the bi-dimensional nature of Graphene and Related Materials (GRM), a new paradigm to tailor interface
properties based on GRM was recently proposed and applied to PSC and modules with the aim to increase both
power conversion efficiency (PCE) and stability of PSCs.[1] Several strategies have been used to master
interface properties with GRM both at the anode and cathode parts of the cell. By dispersing Graphene flakes,
produced by liquid phase exfoliation of pristine graphite, into the mesoporous TiO2 layer and by inserting
graphene oxide (GO) as interlayer between perovskite and Spiro-OMeTAD layers, we demonstrate a PCE of
18.2% with the two-step deposition procedure, carried out in air. The proposed interface engineering strategy
based on GRM has been exploited for the fabrication of state-of-the-art large area perovskite modules. We
indeed demonstrated a PCE of 12.6% on a monolithic module with an active area exceeding 50 cm 2. [2] The use
of GRM permitted to increase the PCE by more than 10% with respect to “conventional” modules, i.e. without
GRM interfaces.
Fig. 1: Perovskite/Graphene solar module.
References
[1] Work in collaboration with F. Bonaccorso (IIT, Italy) and E. Kymakis (TEIE, Crete)
[2] A. Agresti et al. ACS Energy Lett. 2017, 2, 279−287
Donor-impurity-related optical absorption, relative changes of refractive index and
Raman scattering in GaAs elliptic-shaped quantum dots
M. A. Londoño1, R. L. Restrepo2, J. H. Ojeda3, Huynh Vinh Phuc4, M. E. Mora-Ramos5,
E. Kasapoglu6, A. L. Morales7, and C. A. Duque7,*
1
Instituto de Matemáticas, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle
70 No. 52-21, Medellín, Colombia}
2
Universidad EIA, CP 055428, Envigado, Colombia
3
Grupo de Física de Materiales, Universidad Pedagógica y Tecnológica de Colombia, Tunja, Colombia
4
Division of Theoretical Physics, Dong Thap University, Dong Thap, Viet Nam
5
Centro de Investigación en Ciencias-IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad
1001, CP 62209 Cuernavaca, Morelos, Mexico
6
Faculty of Science, Department of Physics, Cumhuriyet University, 58140 Sivas, Turkey
7
Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales,
Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín, Colombia
*
Corresponding autor: C. A. Duque, [email protected]
The conduction band and electron-donor-impurity states in elliptic-shaped GaAs
quantum dots under the effect of an externally applied electric field are calculated within the
effective mass and adiabatic approximations using two different numerical approaches: A
spectral scheme and the finite element method. The resulting energies and wavefunctions
become the basic information needed to evaluate the inter-state optical absorption in the
system, which is reported as a function of the geometry, the electric field strength, and the
temperature. Considering the same parameters, also the relative changes of the refractive
index and the impurity-related Raman scattering are presented. Some results are compared
with available experimental findings reported in the literature.
Fig. 1: Pictorial view of the two structures considered in the present work
Charge transport and softmode excitations in correlated materials mapped by
nonlinear terahertz spectroscopy
Thomas Elsaesser
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie,
12489 Berlin, Germany
Email:[email protected]
Charge dynamics and low-frequency excitations in solids are genuine topics of terahertz (THz)
spectroscopy. While early THz work has focused on the regime of linear light-matter interaction,
the implementation of THz sources for high-field transients offers exciting perspectives for
studying nonlinear processes up to the non-perturbative regime. In the latter, the coupling strength
of the solid’s electrons to the external THz field reaches values comparable to the interactions in
the material. There are new field-resolved techniques of nonlinear THz spectroscopy, in particular
two-dimensional (2D) methods which allow for separating different components of the nonlinear
response and for determining couplings between different excitations [1,2].
In this talk, most recent results from nonlinear THz spectroscopy will be presented. After a brief
introduction of the methods, high-field charge transport in ferroelectrics such as LiNbO3 [3] and the
nonlinear response of softmodes will be discussed. Applying moderate THz driving fields to a
molecular crystal consisting of aspirin molecules, the pronounced correlation of rotational modes of
CH3 groups with collective oscillations of π-electrons drives the system into the regime of
nonperturbative light-matter interaction. Nonlinear absorption around 1.1 THz leads to a blueshifted coherent emission at 1.5 THz, revealing a dynamic breakup of the strong electron-phonon
correlations.
[1] T. Elsaesser, K. Reimann, M. Woerner, J. Chem. Phys. 142, 212301 (2015, perspective article)
[2] M. Woerner, W. Kuehn, P. Bowlan, K. Reimann, T. Elsaesser, New J. Phys. 15, 025039 (2013)
[3] C. Somma et al., Phys. Rev. Lett. 112, 146602 (2014).
Ultrastrong light-matter coupling between metamaterials and two-dimensional
systems
Jérôme Faist, Gian Lorenzo Paravincini Bagliani, Janine Keller, Giacomo Scalari
Institute of Quantum Electronics, ETH Zurich
When a collection of electronic excitations are strongly coupled to a single mode cavity, mixed light-matter excitations
called polaritons are created. The situation is especially interesting when the strength of the light-matter coupling ΩR is
such that the coupling energy becomes close to the one of the bare matter resonance ω . For this value of parameters, the
system enters the so-called ultra-strong coupling regime, in which a number of very interesting physical effects were
predicted. Using metamaterial coupled to two-dimensional electron gases[1], we have demonstrated that a ratio ΩR/ω
close to[2] or above unity can be reached.
0
0
The inherent versatility of metamaterial enables the study of resonators
geometries where the optical field is coupling to very few (less than hundred)
electrons of the two-dimensional electron gas and other where the quality factor
of the resonator can be changed strongly by means of the superconducting to
normal transition[3]. Another interesting feature of these metamaterial is the fact
that they can be coupled using in-plane surface plasmon polaritons, as shown by
the clear anticrossing behaviour displayed by the data (Fig. 1).
Fig. 1. Strong coupling between a LC
resonance of a metamaterial and the
surface-plasmon polariton mode. The
strong coupling model is displayed with a
black solid line with εeff = 11.6 and a
normalized coupling ratio of Ω/ωLC = 3.5
%.
According to theoretical predictions[4], a Dicke superradiant quantum phase
transition is possible in graphene ultra-strongly coupled to an optical resonator,
although the nature of the final phase is still the topic of strong theoretical
interest[5].
Towards exploring this physics, we have recently demonstrated strong coupling
between a metamaterial and a graphene ribbon and its use as efficient THz modulators [6]. We will also show transport
measurements of two-dimensional electron gases in strong coupling with a metamaterial resonator.
[1]
[2]
[3]
[4]
[5]
[6]
G. Scalari, C. Maissen, D. Turcinkova, D. Hagenmuller, S. De Liberato, C. Ciuti, et al., "Ultrastrong Coupling
of the Cyclotron Transition of a 2D Electron Gas to a THz Metamaterial," Science, vol. 335, pp. 1323-1326,
Apr 15 2012.
C. Maissen, G. Scalari, F. Valmorra, M. Beck, J. Faist, S. Cibella, et al., "Ultrastrong coupling in the near field
of complementary split-ring resonators," Physical Review B, vol. 90, p. 205309, Nov 24 2014.
G. Scalari, C. Maissen, S. Cibella, R. Leoni, P. Carelli, F. Valmorra, et al., "Superconducting complementary
metasurfaces for THz ultrastrong light-matter coupling," New Journal of Physics, pp. 1-15, Apr 05 2014.
D. Hagenmüller and C. Ciuti, "Cavity QED of the Graphene Cyclotron Transition," Physical Review Letters,
vol. 109, p. 267403, Dec 2012.
L. Chirolli, M. Polini, V. Giovannetti, and A. H. MacDonald, "Drude Weight, Cyclotron Resonance, and the
Dicke Model of Graphene Cavity QED," Physical Review Letters, vol. 109, p. 267404, Dec 2012.
P. Q. Liu, I. J. Luxmoore, S. A. Mikhailov, N. A. Savostianova, F. Valmorra, J. Faist, et al., "Highly tunable
hybrid metamaterials employing split-ring resonators strongly coupled to graphene surface plasmons," in
Nature Communications vol. 6, ed, 2015.
Pumping up the Sound. Coherent Acoustic Phonon Amplification and
Quantum Cascade Saser Operation in Superlattices
K. Shinokita(1), K. Reimann(1),M. Woerner(1),T. Elsaesser(1) R. Hey(2), C. Flytzanis(3)*(presenter)
(1)Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany
(2)Paul-Drude-Institut für Festkörperelektronik, 10117 Berlin, Germany
(3)Laboratoire Pierre Aigrain, Ecole Normale Superieure, Paris 75231 Paris Cedex 05
*Corresponding author :[email protected]
A central issue in the growing field of phononics, both as regards fundamentals as well
applications, is the generation and amplification of pulsed beams of coherent acoustic phonons with
well prescribed spatiotemporal characteristics. In this respect the transfer of concepts and schemes
from the field of optics and photonics is of central importance in particular as regards parallels with
the generation of coherent pulsed light beams and the laser operation and its extensions and uses.
Here we report the demonstration(1) of a novel amplification scheme of coherent pulsed acoustic
phonon beams based on the photodriven acoustoelectric(AE) effect(2,3) involving folded zone
acoustic phonons(FZAP)(4) in the near THz frequency range in semiconductor superlattices(SL);
0.4THz for the specific supelattices GaAs/AlGaAs, used in the experiments(1) at room temperature,
which can be further tuned and extended with appropriate choice of the structure design.
The amplification is based on the stimulated emission of FZAP by electrically driven electrons
undergoing intra-mini-band transport with copropagating SL acoustic phonons. If the electrons are
traveling faster than the sound through the material, energy can be transferred(2,3) from electrons to
phonons slowing down the former and increasing the number of phonons. The coherent SL phonon is
excited via a displacive mechanism through the spatially periodic absorption of pump light, few tens fs long
pulses, in the GaAs layers of the SL. Electrically driven photoexcited carriers in the GaAs layers generate
via the deformation potential interaction a spatially periodic stress pattern that drives the SL phonon. In the
specific SL used in our study(1), see figure above, the amplification of 200 ps long phonon pulses,
measured by an optical pump-probe delay technique, exceeds 200% over a micron long superlattice
of 70 SL periods, each consisting of a 9.7 nm thick GaAs well and a 1.7 nm thick Al0.3Ga0.7As barrier layer.
The GaAs layers are n-doped with a concentration of 5.2 × 1015 cm-3.
Our amplification concept holds potential for intense robust sources of coherent acoustic phonons
in the sub-THz frequency range and beyond with appropriate SL design and may become a key
ingredient of devices based on sound amplification by stimulated emission of radiation (SASER)(5)
the analogue of the laser with sound with performances well above those of other schemes. Phonons
with sub-THz frequencies have wavelengths in the nanometer range, allowing for investigations with
very high spatial resolution, e.g., in microelectronic devices or in microbiology almost comparable to
that of an electron microscope and can be combined with other micro-diagnostic techniques.
1.K. Shinokita, K. Reimann, M. Woerner, T. Elsaesser, R.Hey and C. Flytzanis, Phys. Rev. Lett 116, 075504
(2016).
2. R. H. Parmenter, Phys. Rev. 89,990 (1953); G. Weinreich and H. G. White, Phys. Rev. 106, 1104 (1957).
3. For a review, see N. I. Meyer and M. H. Jørgensen, in Festkörperprobleme X, edited by O. Madelung
(Vieweg, Braunschweig, 1970). pp. 21–124.
4.M. A. Stroscio and M. Dutta, Phonons in Nanostructures, Cambridge Uni Press 2001.
5.J.C. Jackson, Plasma Phys. Controlled Fusion 28, 669(1986) ; I.V Volkov,S.T.Zavtrak, I.S. Kuten, Phys. Rev.
E 56, 1097 (1997); R.P.Beardsley A.V. Akimov, M. Henini and A.J Kent Phys. Rev Lett 104, 085501 (2010).
Local field effects and optical properties of semiconductor
nanostructures
S. G. Tikhodeev1;2;3, V.D. Kulakovskii2 and N. A. Gippius4;1,
1
A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilova Street 38,
Moscow 119991, Russia
2
Institute of Solid State Physics, Russian Academy of Science, Chernogolovka 142432, Russia
3
M. V. Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia
4
Skolkovo Institute of Science and Technology, Novaya Street 100, Skolkovo 143025, Russia
Recenly the possibility to control the polarization state of radiation from quantum
dots embedded in chiral photonic crystal structures made of achiral planar GaAs waveguides
and microcavities has been demonstrated [1-5]. A chiral partial etching of the waveguide
layer modifies the electromagnetic mode structure and results in a high circular polarization
degree of the quantum dot emission in the absence of external magnetic field. The possibility
to control the polarization state of radiation from quantum emitters has drawn attention of
researchers in recent years as it opens various important applications in spin-optoelectronics,
quantum information technology, chiral synthesis and sensing. A very effective method to
produce the circularly polarized light emission is a fabrication of chiral nanostructures from
achiral semiconductor materials. The optimized structures demonstrate strong circularly
polarized photoemission of QD at zero magnetic field with the degree of circular polarization
up to 90%.
The physical nature of the effect can be understood in terms of the reciprocity
principle taking into account the structural symmetry. We present theoretical description of
the cavity and Bragg mirror modes interference and analyse the local field patterns
responsible for the observed polarization effects.
REFERENCES
1. K. Konishi, M. Nomura, N. Kumagai, S. Iwamoto, Y. Arakawa, and M. Kuwata-Gonokami
“Circularly Polarized Light Emission from Semiconductor Planar Chiral Nanostructures,”
Phys. Rev. Lett., Vol. 106, 057402, 2011.
2. S. V. Lobanov, T. Weiss, N. A. Gippius, S. G. Tikhodeev, V. D. Kulakovskii, K. Konishi,
and M. Kuwata-Gonokami, “Polarization control of quantum dot emission by chiral photonic
crystal slabs,” Opt. Letters , Vol. 40, No. 7, 1528, 2015.
3. A. A. Maksimov, I. I. Tartakovskii, E. V. Filatov, S. V. Lobanov, N. A. Gippius, S. G.
Tikhodeev, C. Schneider, M. Kamp, S. Maier, S. Höfling, and V. D. Kulakovskii, “Circularly
polarized light emission from chiral spatially-structured planar semiconductor
microcavities”, Phys, Rev. B, Vol. 89, 045316, 2014.
4. S. V. Lobanov, S. G. Tikhodeev, N. A. Gippius, A. A. Maksimov, E. V. Filatov, I. I.
Tartakovskii, V. D. Kulakovskii, T. Weiss, C. Schneider, J. Geßler, M. Kamp, and S. Höfling,
“Controlling circular polarization of light emitted by quantum dots using chiral photonic
crystal slabs,” Phys, Rev. B, Vol. 92, 205309, 2015.
5. A. A. Demenev, V. D. Kulakovskii, C. Schneider, S. Brodbeck, M. Kamp, S. Höfling, S.
V. Lobanov, T. Weiss, N.A. Gippius, and S. G. Tikhodeev, “Circularly polarized lasing in
chiral modulated semiconductor microcavity with GaAs quantum wells”, Appl. Phys. Lett.
109, 171106 (2016)
Nonlinear optical properties of excitons
in two-dimensional transition metal dichalcogenides
M.M. Glazova,b*
a
b
Ioffe Institute, 194021, St.-Petersburg, Russia
Spin-optics laboratory, St.-Petersburg State University, 198504, St.-Petersburg, Russia
* Corresponding author: [email protected]
Two-dimensional semiconductors attract an increased interest nowadays due to fascinating properties and
prospects for applications in the fields of spintronics, valleytronics and nanophotonics. Optical properties of
transition metal dichalcogenide monolayers (TMD MLs) such as MoS2, WSe2 are governed by the
Coulomb-correlated electron-hole complexes: neutral and charged excitons. Neutral excitons have significant, up
to 0.5 eV, binding energies owing to relatively weak screening of the Coulomb interaction and rather large
charge carriers effective masses, as compared with conventional two-dimensional semiconductor nanostructures
based on III-V and II-VI materials. The excitons possess high oscillator strength and control the optical response
of TMD MLs up to the room temperature.
The TMD MLs are noncentrosymmetric (the point symmetry group is D3h) and allow for the second
harmonic generation in the electro-dipole approximation. Experiments demonstrate giant enhancement of the
second harmonic generation at the exciton resonances [1], which demonstrates that excitonic states are active
both in single- and two-photon absorption processes. We develop the microscopic theory for the nonlinear
optical response on excitons in TMD MLs. We demonstrate that both intrinsic, related with D3h point symmetry
of TMD MLs, mixing of s- and p-shell excitons and two-step ``allowed-allowed’’ two-photon transitions via
remote band give rise to the second harmonic generation. The developed theory [2] is in good agreement with
the available experimental data.
We also discuss another nonlinear effect, namely, upconversion photoluminescence observed under resonant
excitation of 1s-exciton in WSe2 monolayer. Here the emission of excited excitonic states at ~100 and 400 meV
above the ground 1s exciton state is observed. The model of the effect is based on the Auger-like 1s
exciton-exciton annihilation accompanied with the formation of the excited excitons. Interestingly, that a
substantial circular polarization of the upconversion photoluminescence is observed, whose sign is reversed as
compared with the helicity of excitation. The polarization degree increases linearly with an increase in the
excitation intensity. This effect is interpreted in the framework of valley-selective Bose-stimulated exciton
scattering towards the ground state [3].
References
[1] G. Wang, X. Marie, I. Gerber, T. Amand, D. Lagarde, L. Bouet, M. Vidal, A. Balocchi, and B. Urbaszek, Phys.
Rev. Lett. 114, 097403 (2015).
[2] M. M. Glazov, L. E. Golub, G. Wang, X. Marie, T. Amand, and B. Urbaszek, Phys. Rev. B 95, 035311 (2017).
[3] M. Manca, M. M. Glazov, C. Robert, F. Cadiz, T. Taniguchi, K. Watanabe, E. Courtade, T. Amand, P. Renucci,
X. Marie, G. Wang, B. Urbaszek, arXiv:1701.05800; Nature Communs., in press (2017).
Quantum light emission from InGaAs quantum dots and 2D materials
S. Höfling a, b*, Y.-M. He a, S. Gerhardt a, S. Unsleber a, O. Iff a, N. Lundt a and C. Schneider a
Physik and Wilhelm Conrad Röntgen Research Center for Complex Materials, University of
Wuerzburg, Germany
b SUPA, School of Physics and Astronomy, University of St Andrews, at Andrews, UK
* Corresponding author: [email protected]
a Technische
Solid state quantum emitters are excellent candidates for on-chip quantum light emission, as they promise
ultra-compact integration into complex devices and a vast flexibility of engineering their properties via advanced
crystal growth and lithography techniques. While In(Ga)As quantum dots probably can still be considered as the
prime example of a quantum emitter in solid and we will present high efficiency, high purity, and high
insitsinguishability of single photons emitted from semiconductor micropillar cavities [1,2], the emergent class
of two dimensional transition metal dichalcogenides has recently as an interesting alternative for single photon
emisison. Surprisingly, monolayers of WSe2 exposed to an open surface have been identified to host optically
active defects which promote single photon emission, and as such represent a class of solid state emitters which
do not suffer from a dramatic reduction of brightness via total internal reflection on the air interface.
Here, we study the properties of optically active defects in WSe2, exfoliated on SiO2 as well as GaInP
substrates [3]. We unambiguously demonstrate single photon emission from such defects by measuring the
second order autocorrelation function yielding a value of g2(0) < 0.3. By investigation the decay dynamics of
such emitters, we map out a significant contribution of the dark state contribution, which is the ground state in
WSe2, to the emission process. We furthermore verify, that the integration of monolayers of transition metal
dichalcogenides with epitaxially grown semiconductor material leads to a strong reduction of detrimental
environmental effects, such as spectral jittering and uncontrolled charging, which paves the way towards a
generation of high quality, bright quantum emitters and photon pair emitters in emerging two dimensional
materials.
(left) High resolution microphotoluminescence spectrum of quantum dot like emitter in WSe 2. (right) second
order autocorrelation function of the emitter.
References
[1] X. Ding, Y. He, Z.-C. Duan, N. Gregersen, M.-C. Chen1;2;3, S. Unsleber5, S. Maier, C. Schneider, M. Kamp,
S. Höfling, C.-Y. Lu and J.-W. Pan, Phys. Rev. Lett. 116, 020401 (2016).
[2] S. Unsleber, Y.-M. He, S. Gerhardt, S. Maier, C.-Y. Lu, J.-W. Pan, N. Gregersen, M. Kamp, C. Schneider
and S. Höfling, Opt. Express 24, 8539 (2016).
[3] Y.-M. He, O. Iff, N. Lundt, V. Baumann, M. Davanco, K. Srinivasan, S. Höfling, C. Schneider
Nature Comm. 7, 13409 doi: 10.1038/ncomms13409 (2016).
Nitride nanostructures a source for non-classical light emission
A. Hoffmann
Technische Universität Berlin, Institut für Festkörperphysik,10623 Berlin, Germany
Studying quantum effects in nitride-based nanowires and quantum dots with diameters scaling
down to a few nanometers is hindered by their still mostly bulk-like properties. A drastic
diameter reduction towards the domain of the so-called quantum wires (QWRs) and dots
(QDs) facilitates true one dimensionality of the structures exhibiting confinement in two
directions, while the third direction can straight forwardly be tailored. If the QWR and QDs
length is now sufficiently reduced one can approach the transitional regime between one- and
zero-dimensional structures with drastic effects on the observed emission line characteristics
and photon statistics.
First, GaN QWRs are segregated by plasma-assisted molecular beam epitaxy (PAMBE) on
an AlN/GaN nanowire template. The around 1.5 - 4 nm wide QWRs were deposited on the aplane facets formed at the six intersections of the m-plane sidewalls exposed by individual
AlN/GaN nanowires. By tuning the QWR length from 500 nm to below 50 nm we can
approach the regime of QD-like emission characteristics as demonstrated by the comparably
narrow (1 – 10 meV) emission lines observed in μPhotoluminescence spectra. Interestingly,
some of the emission lines exhibit a linear scaling behavior with excitation power pointing
towards their excitonic character, while other emission line intensities rise in a quadratic
manner. This scaling behavior for the two emission lines is typical for excitonic (X) and
biexcitonic (XX) emission arising from a single GaN QWR. Most of such individual emission
lines even show characteristic traces of single-photon emitters like GaN/AlN quantum dots if
their g2-correlation functions are considered. Temperature dependent series of g2-correlation
functions for the exciton that is dominated by a bunching effect overlaid by a temporally
narrow antibunching as a trace of the onset of single photon emission common for zerodimensional structures. With the raise of temperature both phenomena rapidly fasten and
approach the time resolution of the applied, UV-enhanced Hanbury-Brown and Twiss setup,
leaving behind only a weak bunching trace in the g2-correlation function at a temperature of
30 K. However, by tuning the QWR length we gain access towards a tuning of such photon
statistics, striding the borderline between one- and zero-dimensional structures.
Second, two-photon emission from the biexciton cascade of a single quantum dot, as
representative of a four-level system, can exhibit a super-Poissonian photon distribution in
contrast to the sub-Poissonian statistics of, e.g., polarization-entangled photon pairs. In
particular, we demonstrated experimentally and theoretically how bunched two-photon
emission from a single quantum dot can be tuned by means of the biexciton binding energy,
pump power, and temperature up to 50 K. Variation of these parameters enables control over
the emission from sub- Poissonian one- to super-Poissonian two-photon processes, as
explicitly expressed by the reported bunching phenomenon. Alternative common
interpretations for a bunching signature in the g(2) -correlation function based on purely
biexcitonic single-photon emission or spectral diffusion have been ruled out demonstrating
the importance of two-photon processes in the biexciton cascade. Moreover, we outlined that
the antibunching in the g(2) -correlation function of a “single” photon emitter can be overlaid
by the reported bunched two photon process as long as the biexciton state is still populated.
Our results prove that the full nature of the four-level system must not be neglected as in twolevel based approaches, which evidently only consider one-photon processes.
Bosonic Cascade Lasers
A.V. Kavokina,b
a
Physics and Astronomy, University of Southampton, Highfield, Southampton, SO171BJ, UK
Spin Optical Laboratory, State University of St-Petersburg, 1, Ulianovskaya, St-Petersburg, 198504, Russia
b
Figure 1: The schematic of a bosonic
cascade laser (a). The stimulated
coherent terahertz emission is
generated due to the cascade of
radiative transition between exciton
states confined in a parabolic
quantum well (b) embedded in a
semiconductor microcavity. The final
state of the cascade is a condensate of
exciton-polaritons maintained by
optical pumping. It provides the
bosonic amplification factor of the
terahertz generation of the order of
105.
In this presentation I will overview the recent progress in realization of bosonic cascade
lasers (BCLs). The concept of this new type of a laser has been proposed in 2013 [1]. It is
based on the stimulation of terahertz emission processes by a final state occupation number,
with a final state being the polariton laser mode. Cascades of terahertz photons are emitted
due to the excitonic transitions in a sequence of equidistant quantum states confined in a
parabolic quantum well. The double stimulation effect may be achieved if the microcavity is
embedded in a lateral terahertz cavity. The quantum efficiency of BCLs is expected to be
significantly higher than 100% due to the cascade action. Recently, the dynamics of polariton
relaxation and optical lasing have been demonstrated in microcavities with embedded
parabolic wells designed for realization of bosonic cascades [2]. In the pump-probe
experiments with pulsed excitation, the optical signal oscillating with the frequencies of 0.9,
2.9, and 4.5 THz has been detected [3]. Theoretically, it has been demonstrated that in
addition to the coherent terahertz radiation, bosonic cascade lasers might emit the
superbunched visible light [4]. Bosonic cascade lasers offer a valuable alternative to quantum
cascade lasers and represent an attractive playground for studies of light-matter condensates.
[1] T.C.H. Liew, M.M. Glazov, K.V. Kavokin, I.A. Shelykh, M.A. Kaliteevski, and A.V.Kavokin,
Proposal for a Bosonic Cascade Laser, Phys. Rev. Letters, 110, 047402 (2013).
[2] A. V. Trifonov, E. D. Cherotchenko, J. L. Carthy, I. V. Ignatiev, A. Tzimis, S. Tsintzos, Z.
Hatzopoulos, P. G. Savvidis, and A. V. Kavokin, Dynamics of the energy relaxation in a
parabolic quantum well laser, Phys. Rev. B 93, 125304 (2016).
[3] A.Tzimis, A. Trifonov, G. Christmann, S.I. Tsintzos, Z. Hatzopoulos, I. Ignatiev, A.V. Kavokin,
P.G. Savvidis, Strong coupling and stimulated emission in single parabolic quantum well
microcavity for terahertz cascade, Appl. Phys. Lett. 107, 101101 (2015).
[4] T.C.H. Liew, Y.G. Rubo, A.S. Sheremet, S. De Liberato, I.A. Shelykh, F.P. Laussy and A.V.
Kavokin, Quantum statistics of bosonic cascades, New J. Phys. 18, 023041 (2016).
Oscillating Focus Microscopy : a new tool for imaging in scattering media
Nikita Kavokine1 and Adam E. Cohen2
1
Laboratoire de Physique Statistique, UMR CNRS 8550, Ecole Normale Supérieure,
PSL Research University, 24 rue Lhomond, 75005 Paris, France
2
Departments of Chemistry, Chemical Biology and of Physics,
Harvard University, and Howard Hughes Medical Institute,
12 Oxford Street, Cambridge, Massachusetts 02138, USA
Optical microscopy is an extremely versatile tool that has applications in fields ranging from quantum optics to
biological imaging. In biology, the use of visible light is crucial, since it allows to maintain the sample alive during
imaging. Biological samples usually consist of some fluorescent reporters embedded in living tissue, which is weakly
absorbing, but strongly scattering. For a long time, the goal of microscopy has been to locate these reporters as precisely
as possible, and thus microscopy techniques were designed to filter out any scattered light, which necessarily carries
less structural information than ballistic light that travels directly from reporter to detector. However, developments
in biology have brought to the field of microscopy a new kind of challenge. Biologists have devised fluorescent reporters
that are sensitive to functional properties of their sample : most importantly, proteins whose fluorescence is sensitive
to neural activity [1]. Thus, when looking, for example, at a mouse brain whose neurons light up when they fire,
biologists want to know whether a given neuron is firing, rather than knowing precisely how their fluorescent protein
is distributed on the neuron’s membrane. The role of the microscope is then to detect the fluorescence changes of
a relatively large object with the best possible signal-to-noise ratio, the challenge being to detect these changes for
objects that are as deep as possible in the biological tissue [2]. For this purpose, it is clearly beneficial to use not only
ballistic, but also scattered light that comes out of the sample ; however, existing microscopy techniques fail to do so.
b)
a)
PMT
Laser
EOD
Variable
pinhole
Scanning
mirrors
Signal
Lock-in
amplifier
Time
Figure 1: a) Simplified scheme of the Oscillating Focus microscopy setup. EOD : electro-optic deflector. b) Principle
of OF microscopy : the laser focus is oscillated in a horizontal plane at a high frequency and the modulated signal is
recorded via lock-in detection.
I am going to present a new microscopy technique that attempts to address this challenge by making optimal use of
scattered light [3]. Our technique is based on confocal microscopy, where a very small pinhole in the detection path
allows to reject any out of focus background, but also filters out the scattered light that carries useful information. We
show, using Monte Carlo simulations of light propagation in a scattering medium, that substantial improvement in
signal-to-noise ratio in confocal microscopy can be achieved by increasing the pinhole size up to an optimal value. To
mitigate the loss in background rejection capacity due to an increased pinhole size, we propose to spatially oscillate
the laser focus at high frequency, while raster-scanning a field of view, and to record the high frequency modulated
signal via lock-in detection. We practically implement this Oscillating Focus (OF) microscopy and show, in tissue
phantoms with controlled properties, that it allows for an improved signal-to-noise ratio over confocal microscopy,
as long as the background fluorescence level is not too high, while retaining its optical sectioning ability. We further
demonstrate that these results are still applicable when imaging cortical mouse brain slices, making OF microscopy
a promising candidate for functional imaging in intact tissue.
References
[1] Ntziachristos, V. Nature Methods 7, 603-614 (2010).
[2] D. R. Hochbaum, et. al., Nature Methods 11, 825 (2014).
[3] N. Kavokine and Adam E. Cohen. Oscillating Focus Microscopy. Submitted.
Nanophotonics with high-index dielectric resonant structures
Yuri S. Kivshar
Nonlinear Physics Center, Research School of Physics and Engineering,
Australian National University, Canberra ACT 2601, Australia
E-mail: [email protected]
Recently, a new branch of nanophotonics has emerged aiming at the manipulation of strong
optically-induced electric and magnetic resonances in high-refractive-index dielectric
nanoparticles. In the design of many nanophotonic structures including optical antennas and
metasurfaces, dielectric resonant nanostructures offer advantages over their metallic
counterparts in terms of reduced dissipative losses and resonant enhancement of both electric
and magnetic fields. This talk will review this emerging branch of nanophotonics
demonstrating that these key advantages can lead to new physical effects and applications. In
particular, we will emphasize the importance of complex linear and nonlinear effects
associated with multipolar light emission near the frequency of the magnetic dipole resonance
including unidirectional emission, Huygens metasurfaces, and multipole harmonic generation.
Flat-band polariton condensates in a 2D Lieb lattice with effective spin-orbit coupling
C. E. Whittaker1, E. Cancellieri1, H. Schomerus2, D. R. Gulevich3, P. M. Walker1, D. Vaitiekus1, B. Royall1, M. S.
Skolnick1 and D. N. Krizhanovskii1,*
1
Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
2
Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
3
ITMO University, St. Petersburg 197101, Russia
*corresponding author: [email protected]
The Lieb lattice is at the forefront of research into fundamental effects in condensed matter physics. The
characteristic flat bands which are linear eigenmodes of the system allow high-Tc superconductivity, exotic
ferromagnetism and a wealth of topological phases 1 . Lieb lattice models with on-site interactions permit the
observation of unconventional localization effects, nonlinear compactons and interaction-induced topological states.
Exciton-polaritons arising from strong hybridization of photons and excitons, have recently emerged as an attractive
candidate for studying interacting bosons in lattice potentials [2]. Giant nonlinearity3 and a small effective mass allow
nonequilibrium Bose-Einstein condensation at elevated temperatures, and the spatial, spectral and pseudospin
(polarization) properties of the polariton wave functions are directly accessible due to the finite cavity lifetime.
We report for the first time a 2D Lieb lattice of coupled micropillars in a GaAs-based microcavity with 3
In0.04Ga0.96As quantum wells. We optically load high-density polariton phases into the lattice, observing condensation
into two separate flat bands associated with the ground and first excited pillar modes: photonic “orbitals” with S- and
P-like symmetries respectively. Condensation also occurs in the negative effective mass states at the Brillouin zone
edges (on the S anti-bonding band). Resolving the emission of the flat-band condensates in polarization reveals
pseudospin textures extended across several unit cells due to an effective photonic spin-orbit coupling (SOC) term,
which arises from polarization sensitive tunneling rate of polaritons between adjacent micropillars. Furthermore,
strong interactions lead to a spatially inhomogeneous spectral fragmentation, showing the high sensitivity of flat-band
particles to interactions. Our work highlights the potential of polaritons for emulating solid state Hamiltonians with
interactions and SOC terms.
(c)
(b)
(d)
(e)
Energy (eV)
(a)
momentum
FIG. 1. (a) SEM image of the lattice labeled with sublattices, one unit cell and one lattice constant. (b) Single-particle band
structure with tight-binding curves. (c,d) Real space images of the S and P flat band condensates. (e) Pseudospin textures of the
P flat band in the horizontal-vertical (upper) and diagonal-antidiagonal (lower) bases.
1
Heikkilä, T.T., et al. JETP Lett. 94, 233 (2011)
2
Amo, A, and Bloch, J. C. R. Physique 17, 934–945 (2016)
3
Walker, P. M. et al. Nat. Commun. 6 8317 (2015)
Realization of an atomically thin mirror using monolayer MoSe2
Martin Kroner, Patrick Back, Aroosa Ijaz, Sina Zeytinoglu, and Atac Imamoglu
Institute for Quantum Electronics, ETH Zurich
Advent of new materials such as van der Waals heterostructures, propels new research directions in
condensed matter physics and enables development of novel devices with unique functionalities. In my
presentation, I will show experimental results that a monolayer of MoSe2 embedded in a charge
controlled heterostructure can be used to realize an electrically tunable atomically thin mirror, that
effects 90% extinction of an incident field that is resonant with its exciton transition. The
corresponding maximum reflection coefficient of 45% is only limited by the ratio of the radiative decay
rate to the linewidth of exciton transition and is independent of incident light intensity up to 400
Watts/cm2.
I demonstrate that the reflectivity of the mirror can be drastically modified by applying a gate voltage
that modifies the monolayer charge density. Our findings could find applications ranging from fast
programmable spatial light modulators to suspended ultra-light mirrors for optomechanical devices.
Control of THz radiation by Graphene / Carbon based metasurfaces
Polina Kuzhir
Institute for Nuclear problems of belarusian State University, Minsk 220030, Belarus
[email protected]
Three classes of graphene / carbon-based materials that could possess high absorption ability
of electromagnetic (EM) radiation and resonance behavior in THz frequency ranges are
discussed.
(i)
(ii)
(iii)
The ability of graphene [1-3] to absorb THz radiation is analyzed. We show that being
deposited on a properly chosen optically transparent dielectric substrate graphene
multi-layers can provide almost perfect absorption.
It is also possible to develop an easy to use, cheap, 3D printing process [4,5] for
producing 3D structures of sophisticated geometries made of graphene containing
polymer filaments. The 3D printing process makes it possible to fabricate devices
with predefined EM response and almost 0-reflection.
Another interesting option is to use carbon hollow spheres [6] or graphene/dielectric
spheres as meta-atoms for producing 2D/3D meta-surfaces / meta-materials with
desired THz performance.
The peculiarities of EM response of all these carbon based materials are investigated; the
advantages of each type of carbon/graphene structures depending on particular application
are emphasized.
[1] K. Batrakov, et al, Scientific Reports, 4,Article number:7191 (2014)
[2] K. Batrakov, et al, Applied Physics Letters, 108, 123101 (2016)
[3] P.Kuzhir, et al, J. Nanophoton. 11(3), 032504 (2017), doi: 10.1117/1.JNP.11.032504
[4] A. Paddubskaya, et al, Journal of Applied Physics, 119, 135102 (2016)
[5]
R.
Kotsilkova,
et
al,
Journal
of
Applied
Physics 121,
doi: http://dx.doi.org/10.1063/1.4975820
[6] D. Bychanok, et al, Applied Physics Letters, 108, 013701 (2016)
064105
(2017);
Polariton lattices: a novel platform for analogue simulation
Pavlos G. Lagoudakis 1,2 , and Natalia G. Berloff 1,3
Skolkovo Institute of Science and Technology, Russian Federation
2
Dept of Physics and Astronomy, University of Southampton, UK
Dept of Applied Mathematics and Theoretical Physics, University of Cambridge, UK
1
3
We introduce polariton lattices as a new platform for analogue simulation; based on
well-established semiconductor and optical control technologies polariton simulators allow
for rapid scalability, ease of tunability and effortless readability. Polariton condensates
can be imprinted into any two-dimensional lattices either by spatial modulation of the
pumping laser [1] or by lithographic techniques during the growth process [2], offering
straightforward scalability. In the case of optically imprinted polariton lattices with freely
propagating polariton condensates, we recently demonstrated that the phase-configuration
acquired in a polariton dyad or triad is chosen so as to maximise polariton occupancy
[3], while by expanding to square, and rhombic lattices as well as to arbitrary polariton
graphs we simulated annealing of the XY Hamiltonian through bosonic stimulation [4].
By controlling the separation distance, in-plane wavevector, and spin of the injected condensates in polariton graphs, we
acquire several degrees of freedom in the tunability of intersite interactions, whilst the continuous coupling of polaritons
to free photons offers effortless
readability of all the characteristics of the polariton condensates such as energy, momentum,
spin, and most critically their
phase. The above constitute a
unique toolbox for realising intriguing discrete giant vortices,
controllable next nearest neighbour interactions, and dynamic
phase transitions [5], such as the
one shown in the reciprocal and
real space images of 100 coherently coupled condensates. The
top/bottom row corresponds to ferromagnetic/anti-ferromagnetic alignment at two different instances in the time domain upon pulsed excitation, where we have utilised the timedependence of the couplings in the XY-Hamiltonian via the transient in-plane wavevector.
References
[1] G. Tosi, et al., Nature Physics 8, 190194 (2012)
[2] Na Young Kim, et al., Nature Physics 7, 681686 (2011)
[3] Ohadi, H. et al. Phys. Rev. X, 6, 031032 (2016)
[4] Berloff, N.G et al. arXiv:1607.06065 (2016)
[5] Hohenberg and Halperin Rev. Mod. Phys. 49, 435 (1977)
Nonlinear quantum control of Landau systems beyond Kohn’s theorem
C. Langea*, T. Maaga, A. Bayera, S. Baierla, M. Hohenleutnera, D. Schuha, D. Bougearda, R. Hubera, M. Mootzb,
J. E. Sipec, S.W. Kochb, and M. Kirad
a
Department of Physics, University of Regensburg, 93040 Regensburg, Germany
b
Department of Physics, University of Marburg, 35032 Marburg, Germany
c
Department of Physics, University of Toronto, 60 St George St., Toronto, Ontario M5S 1A7, Canada
d
Department of Electrical Engineering and Computer Science, University of Michigan, Michigan 48109, USA
*Corresponding author: [email protected]
High coherence and nonlinear control of superpositions of electronic quantum states is central to
quantum computing. At THz frequencies, the cyclotron resonance is an outstanding reference system with
high coherence warranted by Kohn’s theorem. We show how single-cycle THz transients of an amplitude
of up to 8.7 kVcm-1 facilitate nonlinear quantum control of a Landau system, leading to anharmonic
Landau ladder climbing up to the 6th rung, and population inversion. Strongly coherent four- and sixwave mixing signals revealed through two-dimensional THz spectroscopy unveil dynamic Coulomb
interactions in a setting of nonperturbative light-matter interaction, beyond Kohn’s theorem.
Dynamics in solid-state systems are governed by many-body interactions, often leading to dephasing on
femtosecond time scales. The cyclotron resonance (CR), however, is protected from inter-particle Coulomb
forces by Walter Kohn’s theorem [1]. In this context, sophisticated quantum phenomena such as ultrastrong
light-matter coupling [2], superradiance [3], coherent control [4] or superfluorescence [5] have been
demonstrated. Yet, the absence of nonlinearities excludes many intriguing perspectives such as quantum logic.
Here, we show how nonperturbative THz excitations of a magnetically biased, two-dimensional electron gas
induce strong, coherent nonlinearities [6]. We employ 30-nm-wide GaAs quantum wells n-doped at 1.6 x
1011 cm-2 and biased with a perpendicular magnetic field of 3.5 T, leading to a CR at νc = 1.45 THz. Twodimensional, phase-resolved THz spectroscopy exploits strong, single-cycle THz pulses labelled A to prepare a
highly excited coherent state, and weak pulses B to probe the nonlinear polarization response ࣟnl representing
interactions between the pulses A and B, as a function of their relative delay time τ, and delay time t of pulse B.
According to Kohn’s theorem, ࣟnl should vanish identically. However, we observe strong, coherent modulations
of ࣟnl at multiples of νc along both time axes τ and t, even for moderate amplitudes of ࣟA = 1.4 kVcm-1 and
4.3 kVcm-1 (Figs. 1a,b). Corresponding wave fronts in the time domain are linked to distinct features in the
frequency domain (Figs. 1c,d) which originate in pump-probe as well as four and six-wave-mixing processes in
the non-perturbative regime [6]. These signatures are accompanied by coherent Landau ladder climbing up to the
6th rung, an abrupt drop of coherence for ࣟA > 3 kVcm-1 due to LO phonon interaction, and a red-shift of the CR.
Fig. 1. a,b ࣟnl(t, τ) for two field amplitudes of pulse A. Lines: wave fronts of a pump-probe (black) and a four-wave-mixing process
(red). c,d, Frequency domain of a,b with pump-probe (PP), four (4WM) and six-wave mixing (6WM) signatures indicated by
circles.
Our microscopic theory links these strong, coherent nonlinearities to dynamically enhanced Coulomb
interactions between electrons and dopant ions which arise in a setting of nonperturbative excitation. The
principle of accessing internal degrees of freedom of a many-body quantum system through Coulomb
correlations suggests that the role of massive many-body interactions, thus far considered detrimental to quantum
control, will have to be reassessed.
[1]
[2]
[3]
[4]
[5]
[6]
W. Kohn, Phys. Rev. 123, 1242 (1961).
G. Scalari et al., Science 335, 1323 (2012).
Q. Zhang et al., Phys. Rev. Lett. 113, 047601 (2014).
T. Arikawa et al. Phys. Rev. B 84, 241307(R) (2011).
G. T. Noe II et al., Nature Physics 8, 219 (2012).
T. Maag et al., Nature Physics 12, 119 (2016).
Quantum Cascades with Excitons and Nanoparticles
T. C. H. Liew
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang
Technological University, Singapore
Quantum cascade lasers [1] based on extended semiconductor superlattices have become some of the
highest quantum efficiency sources of terahertz radiation, where they allow multiple terahertz
frequency photons to be generated per input quantum of energy [2].
In this presentation we will consider variants of quantum cascade lasers based on artificial atoms in
the form of excitons [3] and nanoparticles, which give rise to the theoretical concept of bosonic
cascade lasers where stimulated emission plays a fundamental role. We will extend previous theory
into the quantum regime [4], demonstrating the effects of superbunching and coherence formation.
We will also show how nanoparticles with engineered alloy compositions can give rise to very
compact systems for terahertz frequency generation.
[1] J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, and A. Y. Cho, Science, 264, 553 (1994).
[2] J. Liu, J. Chen, T. Wang, Y. Li, F. Liu, L. Li, L. Wang, & Z. Wang, Solid State Comm., 81, 68 (2013).
[3] T. C. H. Liew, M. M. Glazov, K. V. Kavokin, I. A. Shelykh, M. A. Kaliteevski, and A. V. Kavokin, Phys.
Rev. Lett., 110, 047402 (2013).
[4] T. C. H. Liew, Y. G. Rubo, A. S. Sheremet, S. De Liberato, I. A. Shelykh, F. P. Laussy, and A. V. Kavokin,
New J. Phys., 18, 023041 (2016).
Terahertz frequency quantum cascade lasers – from devices to applications
Edmund Linfielda*, Giles Daviesa, Lianhe Lia, Paul Deana, Alexander Valavanisa, and Joshua Freemana
a
School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
* Corresponding author: [email protected]
The terahertz (THz) frequency range of the electromagnetic spectrum has a broad number of potential
applications across the physical, medical, biological and astronomical sciences. Yet its full potential has
historically not been realized owing to the lack of compact, solid state, sources and detectors.
The demonstration of the first terahertz (THz) frequency quantum cascade laser (QCL) in 2002 [1] opened up
a plethora of new opportunities. Peak output powers exceeding 1 W were first demonstrated in 2014 [2], and
these have subsequently been increased to ~2.4 W at 10 K, and ~1.8 W at 77 K [3]. Furthermore, THz QCLs
now operate over a frequency range of ~1 – 5.5 THz, and at temperatures of up to 200 K, with a breadth of
photonic patterning techniques being used to select specific frequencies and control output beam profiles.
Despite this success, and the flourishing research field that has developed, THz QCLs remain extremely
challenging opto-electronic devices to grow epitaxially, each typically consisting of over 1000 separate
interfaces defined to atomic monolayer precision. We will briefly review the growth of GaAs-AlGaAs THz
QCLs by molecular beam epitaxy [3], and explain why, despite the maturity of this materials system and growth
process, there remain challenges to be resolved. However, we will also demonstrate that it is possible to achieve
repeatable THz QCL growth not only on a year-to-year, but also a day-to-day basis.
We will then discuss how THz QCLs can be used in the development of self-mixing imaging systems [5],
which use the quantum cascade laser itself as both a source and coherent detector, enabling: reflection imaging at
distances exceeding 7 m; the demonstration of swept-frequency interferometry [6]; coherent three-dimensional
imaging; and, near-field microscopy [7]. We will also outline the potential of THz QCLs for use as local
oscillators in satellite-based instrumentation for Earth observation and planetary science.
References
[1] R. Kohler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, and D. A. Ritchie, R. C. Iotti,
and F. Rossi, Nature 417, 156 (2002).
[2] L. Li, L. Chen, J. Zhu, J. Freeman, P. Dean, A. Valavanis, A. G. Davies, and E. H. Linfield, Electronics
Letters 50, 309 (2014).
[3] L. Li, L. Chen, J. Freeman, M. Salih, P. Dean, A. G. Davies, and E. H. Linfield, Electronics Letters, accepted
for publication.
[4] L. H. Li, J. X. Zhu, L. Chen, A. G. Davies, and E. H. Linfield, Optics Express 23, 2720 (2015).
[5] for a Review, see: P. Dean, A. Valavanis, J. Keeley, K. Bertling, Y. L. Lim, R. Alhathlool, A. D. Burnett, L. H.
Li, S. P. Khanna, D. Indjin, T. Taimre, A. D. Rakic, E. H. Linfield and A. G. Davies, Journal of Physics D 47,
374008 (2014).
[6] J. Keeley, P. Dean, A. Valavanis, K. Bertling, Y. L. Lim, R. Alhathlool, T. Taimre, L. H. Li, D. Indjin,
A. D. Rakic, E. H. Linfield and A. G. Davies, Optics Letters 6, 994 (2015).
[7] P. Dean, O. Mitrofanov, J. Keeley, I. Kundu, L. Li, E. H. Linfield, and A. G. Davies, Applied Physics Letters
108, 091113 (2016).
Hybrid nanostructures for sub-wavelength imaging, nonlinear optics, and chemistry
a
Stefan A Maiera*
Department of Physics, Imperial College London
* Corresponding author: [email protected]
Abstract – We demonstrate how controlled emission of hot electrons in plasmonic nanoantennas
leads to highly localized nanochemistry. This scheme is utilized for the assembly of hybrid metallic
nanoantennas consisting both of top-down fabricated elements, and nanosized colloids. The second
part of the talk will show new results for dielectric and hybrid metallic/dielectric antennas, based on Si,
Ge and GaP, for highly enhanced harmonic generation and surface-enhanced sensing.
Plasmonic nanoantennas with nanoscale gaps act as efficient transducers of
electromagnetic energy from the far to the near field at optical frequencies, creating hot spots
of field energy utilized extensively in surface-enhanced spectroscopy and sensing. Using a
super-resolution localization scheme, we demonstrate direct imaging of these electromagnetic
hot spots via single-molecule emission events, paying careful attention to coupling between
molecular emission and antenna modes, in order to determine the true position of the single
emitters [1]. We then introduce the notion of “reactivity hot spots” — nanosized regions in
plasmonic antennas where hot electrons generated via plasmon decay are emitted. We
demonstrate that control over this emission process can lead to highly localized surface
chemistry [2], allowing the positioning of colloidal nanospheres around bow tie antennas with
high accuracy (Figure 1). A combination of experimental imaging of these reactivity hot spots
and ab initio theory will be used to elucidate this process.
Fig. 1.
Gold nanospheres arranged in the gap of a silver bow tie antenna via localized hot electron
emission [2]. SEM image false-coloured to distinguish between the two materials. The diameter of the gold
spheres is 15 nm.
In the second part of the talk, we will present new results on dielectric and hybrid dielectric/metallic
nanoantennas, focusing on highly enhanced harmonic generation and surface-enhanced spectroscopy under
low-loss conditions. As an example, GaP nanopillars allow to utilize the advantages of dielectric antennas in
terms of low loss and high field confinement throughout the visible regime [3]. We will further show new,
unpublished results on hybrid Si/plasmonic antennas, as highly efficient nanoscale sources of third harmonic
radiation.
REFERENCES
[1] Mack et al., “Decoupling absorption and emission processes in super-resolution localization of emitters in
a plasmonic hot spot”, Nature Communications 8, 14513 (2017)
[2] Cortés et al., “Plasmonic hot electron driven site-specific surface chemistry with nanoscale special
resolution”, Nature Communications (accepted 2017)
[3] Cambiasso et al, “Bridging the gap between dielectric nanophotonics and the visible regime with
effectively lossless GaP antennas”, Nano Letters (accepted 2017)
Graphene for coherent emission of THz radiation
J. Mangeneya*, S. Massabeaua, P. Huanga, S. Hupperta, C. Bergerb,c, W. de Heerb,d, S. Dhillona, J. Tignona, L. A.
de Vaulchiera, R. Ferreiraa
a
Laboratoire Pierre Aigrain, Ecole normale supérieure, PSL Research University, CNRS, Université Pierre et
Marie Curie, Sorbonne Universités, Université Paris Diderot, Sorbonne Paris-Cité, France
b
School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
c
Université Grenoble Alpes/CNRS, Institut Néel, Grenoble, 38042 France
d
Tianjin International Center for Nanoparticles and Nanosystems, Tianjin University, China
* [email protected]
Current terahertz (THz) technologies suffer from the lack of compact room temperature THz sources, limiting
the proliferation of consumer applications. As a consequence, an important activity in this field is dedicated to
developing sources such as photoconductive devices, quantum cascade lasers or exploring new schemes for THz
generation like intracavity difference-frequency generation in mid-infrared quantum cascade lasers. In parallel,
important effort is dedicated to the study of new physical properties within novel materials1. Owing to its gapless
electronic band structure, graphene is gaining increasing attention for new developments in the THz domain2. In
addition, graphene exhibits a large nonlinear optical response arising from the linear carrier energy dispersion,
together with the high electron velocity near the Dirac point3.
0.2
0
2
Frequency (THz)
4
6
8
d
10
Mid-gap states
0.15
0.1
Short-range potentials
0.05
0
Density of states
c
60
30
0
-30
Total
0
10
20
Energy (meV)
30
40
e
without vacancy
with vacancies
EF
0
Energy
391
Spectral Amplitude (a. u.)
b
Scattering time (ps)
a
Electric field (mV/cm)
Here, we will review our achievements showing the potential of multilayer epitaxial graphene for the
emission of coherent THz radiation. We will provide evidence of the existence of interband processes in
graphene at THz frequencies in contrast to conventional semiconductor materials (Fig. 1 a). Indeed, Fermi level
energy in multilayer epitaxial graphene is pinned at the Dirac point by mid-gap states5,6 (Fig.1 b,c). This opens
the route to the development of graphene-based emitters and saturable absorbers relying on interband processes.
We will show that second-order nonlinear effects in graphene excited by femtosecond optical pulses leads to
coherent THz emission ranging from 0.1 to 4 THz4 (Fig. 1 d,e). We will discuss how our findings provide unique
insights on physical properties of graphene such as next-nearest-neighbor couplings, unequal electron and hole
dephasing times and scattering mechanisms at energies very close to the Dirac point.
392
393
Delay (ps)
394
395
6
4
2
0
1
2
Frequency (THz)
3
Figure 1: a) Transmission spectra of graphene as function of temperature. b) Scattering times as a function of
carrier energies. c ) Schematic of the density of states of graphene. d) THz electric field waveform emitted by
graphene and its associated spectrum (e) relying on second order nonlinear effects.
References
[1] L Nevou, E. Giraud, F. Castellano, N. Grandjean, J. Faist, Opt. Exp. 22, 3199 (2014).
[2] A. Tredicucci and M. S. Vitiello, Device, IEEE J. Sel. Topics Quantum Electron. 20, 8500109 (2014).
[3] M. M. Glazov, S.D., Ganichev, Phys. Rep. 535, 101 (2014).
[4] J. Maysonnave et al., Nano Lett. 14, 5797 (2014)
[5] M. Baillergeau et al., Scientific Reports 6, 24811 (2016).
[6] S. Massabeau et al., Physical Review B 95, 085311 (2017)
Nanoscale mapping of carrier lifetimes and diffusion in InGaN/GaN quantum well
a
R. Ivanov,a M. Mensi,a L. Y. Kuritzky,b S. Nakamura,b J. S. Speckb and S. Marcinkevičiusa*
Department of Applied Physics, KTH Royal Institute of Technology, Electrum 229, 16440 Kista, Sweden
b
Materials Department, University of California, Santa Barbara, California 93106, USA
* Corresponding author: [email protected]
InxGa1-xN/GaN quantum wells (QWs) are the main constituents of active regions in GaN-based LEDs and
laser diodes operating in the visible spectral range. Due to the large InN and GaN band gap difference, even
small fluctuations of the local InGaN alloy composition cause large band potential variations. These variations
have a strong influence on the carrier dynamics and device performance. For instance, spatial variations of
recombination times affect quantum efficiency; poor lateral diffusion in a QW plane influences injection
efficiency and lifetime.
Band potential fluctuations in InGaN QWs occur on a subwavelength scale. Thus, to study spatial variations
of recombination and diffusion, a measurement technique with a high spatial resolution is required. Scanning
near-field optical microscopy (SNOM) meets such a requirement allowing to measure photoluminescence (PL)
with a resolution limited by the aperture of a fiber probe (typically ~100 nm). In this work, we develop a
multi-mode SNOM technique that produces maps of surface morphology as well as time-integrated and
time-resolved PL parameters in a single scan. Complemented with far-field time -resolved PL data, time-resolved
SNOM maps allow mapping times of radiative and nonradiative recombination [1]. In addition, a simultaneous
mapping of PL intensity in the illumination-collection ((I-C), PL excited and collected through the probe) and
illumination ((I), PL excited through the probe and collected in the far-field) modes allows estimating anisotropic
diffusion lengths. The principle of the diffusion measurement is based on the properties of I-C and I
configurations. In the I-C mode, the PL intensity at a measurement point is determined by recombination and
carrier out-diffusion from under the probe. In the I mode, only the recombination affects the measured intensity.
Because of this difference, features of the I map broaden (Fig. 1(a), (b)).
(a)
(b)
(c)
Fig. 1. Measured I-C (a) and I mode (b) PL intensity maps, as well as simulated I mode map (c).
The measurements were performed on nonpolar m-plane 8 nm wide single In0.15Ga0.85N QW grown on a
GaN substrate. PL was excited with 400 nm 200 fs pulses directly into the QW. I-C and I mode PL intensity
maps were recorded using two spectrometers with cooled CCD detectors. Time-resolved PL transients were
measured with a time-correlated single photon counter. In the diffusion evaluation, experimental radiative and
nonradiative recombination maps were used to calculate I and I-C mode PL intensity maps by adding anisotropic
diffusion. Diffusion parameters were extracted by minimizing the difference between the simulated and the
measured maps (Fig. 1(b), (c)). A match between these maps was achieved for ambipolar diffusion coefficient
values Dc = 0.21 cm2/s and Da = 0.84 cm2/s for directions parallel and perpendicular to the wurtzite c axis. The
strong diffusion anisotropy is assigned to the anisotropy of the top most valence band.
Reference
[1] R. Ivanov, S. Marcinkevičius, T. K. Uždavinys, L. Kuritzky, S. Nakamura and J. S. Speck, Appl. Phys. Lett.
110, 031109 (2017).
Solid-State Quantum Emitters: Old Friends and New
Mete Atatüre
Cavendish Laboratory, University of Cambridge
Optically active spins confined in solids are model systems offering opportunities for studying
a range of physical phenomena. While self-assembled quantum dots are perhaps the most
mature of such systems offering both spin and photon quality for various quantum
applications, more recent material systems, such as atomically thin van der Waals layers, offer
chances to learn more about the underlying physical proterties through confined excitons. In
this talk, we will look at the state of the art for both physical systems from the perspective of
quantum spin-photon interface formation.
Nanostructured electrochemical sensors and biosensors:
our proposals to the new challenges
Ligia Maria Moretto, Maria Angela Stortini and Paolo Ugo
Laboratory of Electrochemical Sensors,
Department of Molecular Sciences and Nanosystems,
University Ca’ Foscari of Venice
[email protected]
In the last decades, electrochemical sensors are entering and modifying our everyday life, as well
as industrial plants. From smoke detectors to easily usable self care sensors for glucose, as well
as sensors and biosensors for health care, for environment monitoring or to face problems of
terroristic actions using toxic substances, or industrial contaminants found in the environment,
these devices can offer sensitive, selective, and cheap sensing for the increasing challenges
continuously emerging.
In this communication we will present the work carried out in our laboratory, passing from
sensors employing traditional electrodes and going to the new materials able to detect emerging
analytes in different matrices. The development of arrays and ensembles of nanoelectrodes
fabricated by electroless deposition of gold on nanoporous membranes or by e-beam
photolithography , or carbon electrodes obtained by pyrolyzed photoresist technology will be
presented and discussed. Examples of application to the determination of proteins, antibodies,
contaminants demonstrate the potentiality and the excellent performance of these devices. Future
developments will be commented.
Subcycle terahertz quantum optics
A. S. Moskalenko*, M. Kizmann, C. Riek, P. Sulzer, M. Seeger, D. V. Seletskiy, G. Burkard,
and A. Leitenstorfer
Department of Physics and Center for Applied Photonics,
University of Konstanz, Germany
* Corresponding author: [email protected]
I will discuss the time-resolved behavior of the photonic ground state and show that vacuum fluctuations of
its electric field can be directly detected using the linear electro-optic effect [1]. I will sketch the main aspects of
a general paraxial theory of electro-optic sampling of quantum fields developed for this purpose [2]. Our
calculations and the corresponding experimental results demonstrate that nonlinear mixing of a femtosecond
near-infrared probe pulse with the multi-terahertz (mid-infrared) vacuum field in a thin electro-optic crystal leads
to an increase of the signal variance with respect to the shot noise level [1,2]. The detection method avoids
absorption or amplification of photons of the probed quantum field. Applying the theory also to a textbook
example for a broadband squeezed vacuum state, we predicted that temporal oscillations of the electric field
noise can be traced with subcycle resolution [2].
Recently we have demonstrated that with another femtosecond pump pulse interacting with the vacuum in
an additional nonlinear optical crystal (GX), we can modify the field being initially in the ground state that leads
to the generation of pulsed squeezed vacuum states [3]. I will show that the properties of these states can be
explained theoretically via a cascaded χ(2) process in the GX where at first a secondary classical mid-infrared
field transient EMIR(t) is created by the pump and then it acts on the vacuum fluctuations present in around half
the carrier frequency via broadband parametric down-conversion [3]. We introduce a time-dependent squeezing
factor f(t), which within the cascaded χ(2) mechanism is proportional to ∂EMIR(t)/∂t for low maximal squeezing
(and anti-squeezing) as well as for arbitrary squeezing but at the time moments when EMIR(t) vanishes. Solving
then for the whole dynamics in the case of the increased pump intensity we observe an additional broadening of
the time segments with squeezing whereas the segments with anti-squeezing are narrowed (see Fig. 1).
Fig. 1: (a) Dynamics of the classical mid-infrared electric field EMIR(t) and dynamics of quantum noise
amplitude induced by it in the GX. (b) Temporal behavior of the corresponding time-dependent squeezing
factor f(t) calculated as in the low squeezing approximation and from the exact analytical solution.
References
[1] C. Riek et al., Science 350, 420 (2015).
[2] A.S. Moskalenko et al., Phys. Rev. Lett. 115, 263601 (2015).
[3] C. Riek et al., Nature 541, 376 (2017).
Pressure-driven insulator-metal transition in VO2 studied by pump-probe spectroscopy
J. M. Brauna,b, H. Schneidera, M. Helma,b, R. Mirekc, L. A. Boatnerd,
R. E. Marvele, R. F. Haglunde, and A. Pashkina*
a
Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
b
Technische Universität Dresden, Germany
c
University of Warsaw, Poland
d
Oak Ridge National Laboratory, USA
e
Vanderbilt University, Nashville, USA
* Corresponding author: [email protected]
Application of external pressure is an efficient tool for tuning electronic interactions in a broad variety of
strongly correlated systems. Pressure-driven increase of the bandwidth typically decreases correlation effects. As
a result an insulating material may undergo a transition to a metallic state. Vanadium dioxide (VO2) is a prime
example of a transition metal oxide showing an insulator-to-metal transition (IMT) around 340 K accompanied
by a pronounced structural transformation. Pressure-induced metallization of VO2 has been demonstrated by
infrared spectroscopy [1] and resistivity measurements [2]. Remarkably, in contrast to the temperature-driven
IMT, the crystal structure is not affected and remains monoclinic in the metallic phase [1-3].
Here we apply ultrafast optical pump – THz probe spectroscopy in order to study the pressure-induced IMT
in a VO2 crystal. The probe pulses with a central frequency of 30 THz were generated by difference frequency
mixing and focused on the sample mounted inside a diamond anvil pressure cell. The utilized photon energy far
below the bandgap of VO2 enables us a sensitive probing of the metallization dynamics in VO2.
Typical pump-probe dynamics is shown in Fig. 1(a). Above critical excitation fluence, a non-zero
pump-probe signal survives on long timescale indicating the metastable metallic state [4]. We define this critical
threshold fluence th as a crossing point of linearly extrapolated parts of the fluence dependence as shown in Fig.
1(b). Fig. 1(c) shows that th initially increases with pressure evidencing that the monoclinic structure stabilizes
under hydrostatic compression. Surprisingly, we observe the threshold behavior typical for the insulating state of
VO2 also above the IMT, that occurs between 6 and 8 GPa. This may indicate that the Hubbard bands are still
present even in the metallic state - as predicted for a bandwidth-controlled Mott-Hubbard transition. A sudden
drop of th at the IMT may be related to the partial screening of Coulomb correlations by delocalized electrons
in the metallic state, that lowers the critical excitation density necessary for a complete closure of the correlation
gap. Our results show a purely electronic pressure-induced Mott-Hubbard transition in VO2 and yield important
insights into the nature of the correlated metallic state.
2.9 GPa
(a)
8
R/R (%) after 1ps
R/R (%)
6
4
16.8 mJ/cm2
2
13.1 mJ/cm2
0
9.4 mJ/cm2
0
25
20.6 mJ/cm2
1
2
delay time (ps)
3
2.1GPa
5.1GPa
11.3GPa
6
20
th (mJ/cm2)
8
4
2
0
th
0
5
10 15 20
fluence  (mJ/cm2)
25
15
10
5
0
pc
0
5
10 15
pressure (GPa)
20
Fig. 1: (a) Pump-probe signals measured for different excitation fluences  at pressure of 2.9 GPa; (b) Amplitude of
pump-probe in the metastable photoinduced state 1 ps after the excitation at different pressures; (c) Dependence of the
threshold fluence th as a function of applied pressure. pc marks the region of the insulator-metal transition.
References
[1] E. Arcangeletti et al., Phys. Rev. Lett. 98, 196406 (2007).
[2] L. Bai et al., Phys. Rev. B. 91, 104110 (2015).
[3] W.-P. Hsieh et al., Appl. Phys. Lett. 104, 021917 (2014).
Terahertz transitions in double-gated quantum rings
M.E. Portnoi*, T. P. Collier, and V. A. Saroka
School of Physics, University of Exeter, Stocker Road, Exeter Ex4 4QL, United Kingdom
* Corresponding author: [email protected]
Creating portable tunable sources and detectors of THz radiation is one of the most formidable tasks of
contemporary applied physics. One of the recent directions in this quest is the use of non-simply connected
nanostructures such single-walled carbon nanotubes (CNTs) [1] and quantum rings (QRs) [2] in which transition
frequencies can be tuned by an external magnetic field. However, the fields required to achieve a noticeable
effect are prohibitively high. For example, opening a band gap of 1 THz in a (10,10) armchair CNT requires
magnetic field of 6 T [3]. A similar field is required to achieve a flux of a half flux quanta through a ring of a
10nm diameter. Thus, the portability of Aharonov-Bohm-effect-based THz emitter is out of question.
In the presented work, we consider a different setup – a quantum ring with two lateral (in the plane of the
ring) gates placed on the two opposite sides of the ring. These gates can be modelled as two point charges or as
two parallel wires to accommodate an array of rings between them (see Fig. 1). We show that a double-gated
single-electron QR resembles a double quantum well, one of the first semiconductor heterostructures proposed to
be used for THz application. The ring however has a significantly higher tunability. Indeed, the applied voltage
not only controls the height of the barrier between two quantum wells but also the voltage difference on the gates
controls the well separation. There is another important difference between a double-gated ring and a double
quantum well. Namely, in the ring geometry selection rules for interlevel optical transitions excited by the
linearly polarized light incident normally to the ring plane depend strongly on the polarization angle with respect
to the gates. The most striking difference to the double well is that dipole transitions between the ground and the
second excited states become allowed for a range of polarization angles. Therefore, a double-gated QR can be
viewed as a three-level system suitable for lasing between the first excited and the ground state (typically in the
THz range) driven by excitation from the ground to the second excited state at a much higher frequency.
Fig. 1: Geometry of the considered double-gated quantum ring system.
References
[1] R.R.Hartmann, J. Kono, and M.E.Portnoi, Nanotechnology 25, 322001 (2014).
[2] A.M.Alexeev and M.E.Portnoi, Phys. Rev. B 85, 245419 (2012).
Organic-inorganic hybrid structures based on GaN nanorods
Galia Pozina*, Mathias Forsberg, Alexandra Serban, Ching-Lien Hsiao
Department of Physics, Chemistry and Biology, Linköping University, Se-58183, Linköping, Sweden
* Corresponding author: [email protected]
Novel hybrid organic-inorganic nanostructures utilizing non-radiative resonant energy transfer are very
attractive for different nano-optoelectronic applications due to their high internal efficiency for down conversion
of light. We have fabricated and studied hybrid structures based on green polyfluorene (F8BT) and on GaN
(0001) nanorods grown by magnetron sputtering on Si(111) substrates [1]. An interesting phenomena observed in
the GaN nanorods is related to a presence of self-organized polymorphic quantum wells (QW) formed by
stacking faults (SFs), see Fig. 1. This QW structure shows in photoluminescence (PL) a significantly different
polarization property compared to the GaN excitonic transition. Using time-resolved µ-PL, we have investigated
dynamics of the near-band gap luminescence in the bare nanorods and in the hybrid samples. In difference to
GaN excitonic emission, the recombination rate for the SF related luminescence increases in the presence of
polyfluorene film, which can be understood in terms of Förster interaction mechanism. In this assumption, the
efficiency of non-radiative resonant energy transfer in hybrids was estimated to be as high as 35 % at low
temperatures.
Figure 1. (a) Schematic drawing of the hybrid structures formed by GaN nanorod with green polyfluorene.
(b) Transmission electron microscopy (TEM) image showing GaN nanorods, the black square indicates the area
with SFs measured with high resolution TEM as illustrated in (c).
References
[1] M. Forsberg, A. Serban, I. Poenaru, C.-L. Hsiao, M. Junaid, J. Birch, and G. Pozina. Nanotechnology 26,
355203 (2015).
Electronic and Optical properties of topological Dirac and Weyl semimetals
F. Bechstedt(1), A. Mosca Conte(2), D. Grassano(3), and O. Pulci(2,3)
(1)
(2)
Friedrich-Schiller-Universität, Jena, Germany
ETSF, and Mediterranean Institute for Fundamental Physics, Rome, Italy
(3)
Department of Physics, University of Rome Tor Vergata, Rome, Italy
Three-dimensional (3D) topological semimetals of Dirac or Weyl type have been
recently predicted as a new topological state of quantum matters. Because of their
linear bands near the Fermi level, which form 3D Dirac cones at Dirac or Weyl nodes
as illustrated in Fig. 1, they have attracted increasing interest in physics and
materials science. Meanwhile, the realization of such novel quantum matter has been
proven for several crystalline compounds within their semimetallic phase. Here, we
present the exotic band structures of centrosymmetric bct Cd3As2, a Dirac semimetal
(space group I41/cd), and the bct transition metal monopnictides, Weyl semimetals
(space group I41md), as calculated in the framework of a semilocal ab initio density
functional theory including spin-orbit interaction (SOI).
For bct Cd3As2 we find two Dirac points at the tetragonal axis [1], whereas for TaAs,
TaP, NbAs, and NbP four pairs of W1 Weyl nodes with opposite chirality and other
eight W2 Weyl pairs appear in the Brillouin zone [2]. The topological semimetals
exhibit anisotropic Dirac cones with violation of the electron-hole symmetry. The
resulting Fermi velocities are somewhat smaller than that known from graphene. We
show that the Dirac behavior of the electrons is however only valid for small energies
around the Fermi level. Consequently, ARPES measurements at higher energies
have actually studied Kane electrons.
The linear bands and their occupation near the Dirac or Weyl nodes determine the
infrared (IR) optical properties via interband transitions (see Fig. 1) but also Drude
terms in the case of the Weyl semimetals. Similar to two-dimensional graphene, the
imaginary part of the interband dielectric function shows a constant plateau, which is
proportional to the Sommerfeld finestructure constant. The anisotropy of the Dirac
cones governs the polarization dependence of the linear slope of the IR optical
conductivity. The calculated electronic and optical properties are directly compared
with available experimental data. We explain the low-frequency spectra measured for
Cd3As2 and TaAs [1,2].
[1] A. Mosca Conte, O. Pulci, and F. Bechstedt, Scientific Reports (in press).
[2] D. Grassano, O. Pulci, and F. Bechstedt, in preparation.
Fig. 1: Dirac cones in Dirac and Weyl semimetals as influenced by SOI and
symmetry. Optical interband transitions are indicated by vertical red arrows.
On-Chip, wide bandwidth THz frequency comb sources
Giacomo Scalari* a,Markus Roesch a, Andres Ferrer a, D. Bachmann b, K. Unterrainerb, Mattias Beck a, Jérôme
Faist a
a
Institute for Quantum Electronics, Department of Physics, ETH Zürich, Zürich, Switzerland
b
TU Wien, Photonics Institute and Center for Micro- and Nanostructures, Gußhausstraße 27-29, 1040
Vienna, Austria
* Corresponding author: [email protected]
Terahertz (THz) quantum-cascade lasers (QCLs) constitute a very promising candidate for compact, wide
bandwidth, integrated frequency combs [1,4-7]. QCLs based on heterogeneous cores display the widest
spectral coverage reaching more than one octave [2]. The possibility to engineer the gain profile turns out to be
fundamental also with respect to dispersion compensation in order to extended the comb spectral bandwidth
[2,7]. In the effort of extending the comb operation to a full-octave to implement the laser self-referencing [3],
we present here a new here a new THz QCL active region that allows the generation of a frequency comb with a
spectral bandwidth exceeding of 1 THz centered at 3.1 THz. The used building block is the three-active region
design reported in Ref. [2], where a design at 3.4 THz has been added to increase the bandwidth towards higher
frequencies. The four designs have central frequencies of 2.3, 2.6, 2.9, and 3.4 THz, the number of periods per
design has also been rearranged in order to provide a flat gain resulting in a similar threshold for all the active
regions and increased dynamic range. Peak powers above 8 mW are recorded at 30 K and the lasing spectrum
spans over 1.94 THz from 1.88 THz to 3.82 THz covering more than a full octave in frequency (Fig.1(a,b)).
Dry-etched lasers with side-absorbers for lateral mode suppression similar as in [5] were fabricated for
continuous wave (CW) operation and comb operation is probed through the beatnote analysis. Fig. 1(c,d) shows
the beatnote as a function of the injected current with a maximum comb span of 1.1 THz which is the broadest
demonstrated so far. Further proof of comb regime comes from the simultaneous measurements of two laser
ridges on the same chip that show multiheterodyne spectra working in a dual-comb configuration [6].
Fig. 1 (a): . Optical spectrum of a 1.5mm x 150µm wet-etched laser in pulsed (20 % d.c.) at 20 K. (b) Optical spectrum of a 1.8 mm x 60 µm
dry-etched laser in CW operation at 21 K. (c) Intermode beatnote of a 2 mm x 60 µm dry-etched laser as a function of the driving current.
(T=20 K). The beatnote signal is extracted from the bias line with a bias-tee (RBW): 10kHz, (VBW): 100 kHz, sweep time (SWT): 10 sec.).
(d) Optical spectrum at 562 mA at 16 Kelvin. For this current the laser is in a FC regime providing a bandwidth of 1.1 THz.
References
[1] D. Burghoff et al., Nature Photonics 8, 462-467 (2014)
[2] M. Rösch, G. Scalari, M. Beck, and J. Faist, Nature Photonics 9, 42-47 (2015)
[3] T. Udem, R. Holzwarth, T. W. Hänsch, Nature 416, 233 (2002).
[4] J. Faist, G. Villares, G. Scalari, M. Rösch, C. Bonzon, A. Hugi, and M. Beck, Nanophotonics 5, 272 (2016).
[5] D. Bachmann, M. Rösch et al., Optica 3, 1087–1094 (2016)
[6] M. Rösch, G. Scalari, G. Villares, L. Bosco, M. Beck, J. Faist, Appl. Phys. Lett. 108, 171104 (2016)
[7] D. Bachmann, M. Rösch, G. Scalari et al., Appl. Phys. Lett. , 109, 221107 (2016)
3D and 2D topological insulators in the regime of electromagnetic dressing
Ivan A. Shelykh a,b*, Dmirty Yudin a, Ivan Iorshd and Mehedi Hasanc
a
ITMO University, St. Petersburg 197101, Russia
Science Institute, University of Iceland, Dunhagi-3, IS-107, Reykjavik, Iceland
c
Division of Physics and Applied Physics, Nanyang Technological University 637371,
Singapore
b
* Corresponding author: [email protected]
We show theoretically that strong electron coupling to THz light drastically modifies
transport properties of 3D and 2D topological insulators.
In 3D case coupling to linear polarized field makes electron dispersion strongly
anisotropic and leads to suppression of spin currents in the system [1]
In 2D case of HgTe quantum well, in which band inversion occurs above a critical value
of the well thickness, strong light- matter coupling provides a very powerful tool to control
topological transitions, even for a thickness of the quantum well that is below the critical
value where normally topological edge states occur. We show that topological phase
properties of the edge states, including their group velocity, can be tuned in a controllable way
by changing the intensity of the laser field. These findings open up for new experimental
means with which to investigate topological insulators. Importantly, all the topological effects
discussed here can be realized in a controllable and reversible manner, simply by changing the
intensity of the electromagnetic radiation [2]
References
[1] Dmitry Yudin, Oleg Kibis and Ivan Shelykh, New J. Phys. 18, 103014 (2016)
[2] Mehedi Hasan, Dmitry Yudin, Ivan Iorsh, Olle Eriksson, Ivan Shelykh, arXiv:1701.06756
Finite temperature disordered bosons in two dimensions
G.V. Shlyapnikov
LPTMS, CNRS, Univ. Paris Sud, Orsay 91405 and SPEC, CEA, CNRS, Universite Paris-Sacley,
Gif sur Yvette 91191, France
Russian quantum Center, Skolkovo, Moscow region 143025, Russia
I study phase transitions in a two-dimensional weakly interacting Bose gas in a random potential at
finite temperatures. I identify superfluid, normal fluid, and insulator phases and construct the phase
diagram. At $T=0$, there is a tricritical point where the three phases meet each other. It is shown that
in the thermodynamic limit the insulator phase does not exist at temperatures exceeding a certain
critical value, and at lower temperatures all phase transitions occur when the interaction energy per
particle is of the order of the characteristic disorder energy.
Light propagation in crystals, resonant photonic crystals,
and van der Waals heterostructures
T.V. Shubina
Ioffe Institute, 194021 St. Petersburg, Russia
[email protected]
The deterministic delay of short optical pulses, in other words – the slow light, is currently of
particular interest, being one of the key elements in quantum information processing. It
exploits basically a sharp change in the refractive index in a dispersive medium, which results
in the decrease of a group velocity. In particular, such phenomenon has been observed in
crystals of wide-gap semiconductors near excitonic resonances possessing strong oscillator
strength [1-3]. Another promising way of light retardation is the use of photonic crystals, in
which the light dispersion is distorted near the Bragg frequency leading to the appearance of
the so-called slow optical modes. The resonant photonic crystals (RPCs), where exciton
resonances in quantum wells (QWs) and Bragg resonances occur at close frequencies [4], turn
out to be particular promising for such application. Theoretical consideration exhibited the
presence of a narrow dip in their stopbands, where the delayed light pulse can propagate
without dramatic attenuation. However, previous experimental studies of RPCs with a
primitive unit cell have shown that the delay of a ps pulse can hardly exceed its temporal halfwidth and that the signal attenuation is too strong. Recently, we have demonstrated the
advantages of RPCs with the unit cells of complex designs, which comprise either wells with
slightly detuned excitonic resonances or barriers of variable widths (that destroys the Bragg
condition). The slope of the slow modes can be efficiently controlled in both cases. In such
structures, the group velocity of the ps pulse can be reduced by a factor of 50 as compared to
the light velocity in vacuum with a damping of only 3–5 times [5]. Besides, we have
performed the studies of the light propagation through van-der-Waals (vdW) heterostructures
which comprise 2D monolayers, whose position in a stack is consistent with the Bragg
condition as well. These structures represent an original type of RPCs – “a purely resonant
crystal”, where the influence of an active layer thickness can be neglected, while the impact
of dielectric contrast and an increased barrier height may be pronounced. That influences the
dispersion laws and, hence, spectra of reflected and transmitted light. We investigate the vdW
RPCs (e.g., made from 2D WSe2) in comparison with the ordinary RPCs based on II-VI QWs
(ZnSe/ZnMgSSe). The parameters needed for the calculations – the energies, radiative width
(Γ0), and nonradiative width (Γ) of exciton resonances – are obtained by modelling the
reflectance spectra. Our calculations have demonstrated the certain advantages of vdW RPCs
over conventional RPCs, such as higher delay (5 ps vs 2 ps) and linear dispersion law of the
slow mode with similar parameters. In addition, intricate optical activity can be realized in the
vdW heterostructures. It worth noting that the development of technology is the prerequisite
for any practical application of investigated structures. This work was supported by the
Government of the Russian Federation (Project # 14.W03.31.0011).
[1] T.V. Shubina et al., Phys. Rev. Lett. 100, 087402 (2008).
[2] T.V. Shubina et al., Phys. Rev. B 84, 075202 (2011).
[3] T.V. Shubina, M.M. Glazov, N.A. Gippius, and B. Gil, in III Nitride Semiconductors and
Their Modern Devices, Oxford Univ. Press, New York, 2013.
[4] E.L. Ivchenko et al., Phys. Rev. B 70,195106 (2004).
[5] D.R. Kazanov, A.V. Poshakinskiy, and T.V. Shubina, JETP Lett. 105, 8-12 (2017).
Controllable spin order in driven-dissipative chains of polariton condensates
H. Sigurðssona*, A. J. Ramseyb, H. Ohadic, Y. G. Rubod,e, T. C. H. Liewf, J. J. Baumbergc, and I. A. Shelykha,g,
a
Science Institute, University of Iceland, Dunhagi-3, IS-107 Reykjavik, Iceland
b
Hitachi Cambridge Laboratory, Hitachi Europe Ltd., Cambridge CB3 0HE, UK
c
Department of Physics, Cavendish Laboratory, University of Cambridge, UK
d
Inst. de Energías Renovables, Univ. Nacional Autónoma de México, Temixco, Morelos 62580, Mexico
e
Center for Theoretical Physics of Complex Systems, Inst. for Basic Science, Daejeon 34051, Republic of Korea
f
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang
Technological University 637371, Singapore
g
ITMO University, St. Petersburg, 197101, Russia
* Corresponding author: [email protected]
The physics of many-body spin lattices have widespread implications in fields as diverse as combinatorial
optimization problems, and simulation of neural networks and protein folding. Numerous spin lattice
Hamiltonians have been constructed to understand the plethora of spin physics such as spin ice, frustration, spin
wave propagation, skyrmion dynamics, and domain wall propagation. Realizing a controllable spin lattice is an
important step towards setting up the playground and understanding all of these intriguing spin phenomena.
Driven-dissipative spin lattices where the system is characterized by a balance of gain and decay have
only recently been realized using exciton-polariton condensates [1,2,3]. The condensates are nonresonantly driven
above a critical occupation threshold where they undergo spontaneous spin bifurcation (magnetization) forming
a binary chain of spin-up or spin-down states. The transport of polaritons from one condensate to another can be
regarded as a type of coherent coupling making the system an interesting spin lattice candidate.
We solve analytically and investigate numerically magnetic order in a chain of driven-dissipative spinor
condensates (Fig.1a) accounting for nearest neighbor coupling in the tight binding approach. Minimization of the
bifurcation threshold determines the magnetic
order as a function of the coupling strength.
This allows one to controllably produce
multiple magnetic orders via adiabatic (slow
ramping of) pumping. In addition to
ferromagnetic
(FM)
(Fig.1b)
and
anti-ferromagnetic (AFM) (Fig.1c) ordered
states we show the formation of a paired-spin
(P) ordered state (Fig.1d) as a consequence of
the phase degree of freedom between
condensates. We find that the lowest bifurcation
threshold states have well defined phase slips
between condensates and are stable against
long-wavelength fluctuations. Monte-Carlo
trials with adiabatic ramping of the pump
intensity give a phase diagram in full agreement
Fig. 1: (a) Schematic showing spinor condensates coupled
with the predicted minimum threshold winners
together through the same-spin coupling parameter J in an
as a function of coupling strength. This clear
infinite chain. States with equal number of bond types per
hierarchy for the probability of magnetic order
condensate can be categorized as (b) FM, (c) AFM, and (d)
is an important prerequisite for a spin-lattice paired (P).
simulator.
References
[1] Ohadi, H. et al. Spontaneous Spin Bifurcations and Ferromagnetic Phase Transitions in a Spinor
Exciton-Polariton Condensate. Phys. Rev. X, 5, 031002 (2015).
[2] Ohadi, H. et al. Tunable magnetic alignment between trapped exciton-polariton condensates. Phys. Rev. Lett.
116, 106403 (2016).
[3] Dreismann, A. et al. A sub-femtojoule electrical spin-switch based on optically trapped polariton condensates.
Nature Materials, 15, 1074–1078 (2016).
Ultra-strong coupling with the free space: the superradiance
S. Huppert, A. Vasanelli, Y. Todorov and C. Sirtori
Paris Diderot, Sorbonne Paris Cité, Laboratoire Matériaux et Phénomènes Quantiques,
UMR7162, 75013 Paris, France
Light-matter interaction, usually considered only as a weak probe, becomes the dominant
energy relaxation mechanism for collective excitations in a two-dimensional electron gas.
Indeed, when the concentration is sufficiently high, electrons respond to the solicitation of
photons as a whole, with an absorption spectrum presenting a single resonance at a
completely different energy with respect to that of the electronic transitions [1]. This optical
resonance corresponds to a many-body excitation of the system that ties together all dipoles,
thus presenting a huge interaction with light. The spontaneous emission rate becomes
proportional to the number of particles taking part in the collective excitation, a phenomenon
known as superradiance [2]. In systems with very high electronic density, spontaneous
emission is therefore the dominant relaxation mechanism and the associated broadening can
even become a sizable fraction of the resonance frequency. This physical situation is correctly
described only by taking into account the anti-resonant terms of the light-matter interaction
Hamiltonian similarly to the ultra-strong coupling regime in micro-cavities [3]. In recent
experiments we showed that the collective excitation can reach the regime of strong coupling
with free space radiation, where the radiative broadening ħΓrad dominates over the nonradiative broadening [4]. We also show that this superradiant behavior is associated with a
cooperative Lamb shift of the resonance frequency, arising from emission and absorption of
virtual photons. This work opens exciting perspectives, as it enables achieving ultra-strong
coupling [5] and paves the way to the observation of novel quantum effects in open systems,
without any light confinement.
Fig. 1. Normalized incandescent emission spectra, for three quantum wells with three
different electronic densities Ns. Note the increased width due to enhanced radiative decay.
References
[1] B. Askenazi, A . Vasanelli, A. Delteil, Y. Todorov, L.C. Andreani, G. Beaudoin, I. Sagnes
and C. Sirtori, New J. Phys. 16, 043029 (2014).
[2] R. H. Dicke, Phys. Rev. 93, 99 (1954).
[3] C. Ciuti, G. Bastard, and I. Carusotto, Phys. Rev. B 72, 115303 (2005).
[4] T. Laurent, Y. Todorov, A. Vasanelli, A. Delteil, I. Sagnes, G. Beaudoin, and C. Sirtori,
Phys. Rev. Lett., 115, 187402 (2015).
[5] S. Huppert, A. Vasanelli, G. Pegolotti, Y. Todorov,C. Sirtori, arXiv 1604.01668 (2016).
Tamm plasmon/surface plasmon mode beating for spatially controlled plasmon
generation
C. Symonds1*, S. Azzini1, G. Lheureux1, P. Senellart2, A. Lemaitre2, J.-J. Greffet3, C. Sauvan3, C. Blanchard3, J.
Bellessa1
1
Institut Lumière Matière, Université de Lyon, UMR5306 Université Claude Bernard Lyon1-CNRS, 69622
Villeurbanne, France,
2
Centre de Nanosciences et Nanotechnologies, CNRS Université Paris-Saclay, Route de Nozay, F-91460
Marcoussis, France
3
Laboratoire Charles Fabry, Institut d’Optique CNRS, Université Paris-Sud, 91127 Palaiseau, France
* Corresponding author: [email protected]
Tamm plasmons (TPs) are electromagnetic modes formed at the interface between a photonic structure and a
metallic layer [1]. They present optical properties at the boundary between microcavity modes and surface
plasmons (SP). Compared to conventional SPs, Tamm plasmons present the advantage to be radiative and also to
have reduced losses due to the larger penetration of the electric field in the dielectric part of the structure. The
coupling between TP and semiconductor nanostructures (quantum dots, quantum wells) have led to the
experimental demonstration of bright single photon sources [2], TP-exciton polaritons [3], and polarized laser
emission [4]. Another very promising feature of TP modes is that they coexist outside the lightcone with the
conventional SP present at the metal/air interface [5].
Here, we will report on the experimental observation of the electromagnetic coupling between TP and SP
modes in a novel metal/semiconductor integrated structure comprising a buried quantum dot-based light source
and a metallic surface grating for light extraction (Figure 1). The TP mode is excited by the photoluminescence
emission of quantum dots grown in the top part of the dielectric mirror. This allows for indirect excitation of the
SP at the silver/air interface, provided that a non-negligible spatial overlap between the two modes takes place in
the thin metallic layer. The hybrid nature of such a TP/SP mode propagating in the planar silver thin film is
demonstrated by the observation of a spatial beating along the propagation. This beating turns out to be in very
good agreement with the results of numerical calculations, based on the wave-vector mismatch existing between
the two modes. Our results pave the way to a new generation of hybrid metal/semiconductor integrated optical
devices for both energy-sensitive surface detection and excitation of surface plasmons via Tamm plasmons.
Figure 1: (a) Image of the sample surface comprising a grating (period 0.9 µm) on its upper part. (b) Fourier
imaging of the emission showing the TP (solid lines) and SP (dashed lines) band folding when exciting directly
on the grating.
[1] M. Kaliteevski et al., Tamm plasmons-polaritons: Possible electromagnetic states at the interface of a metal
and a dielectric Bragg mirror, Phys. Rev. B 76, 165415 (2007)
[2] O. Gazzano et al., Single photon source using confined Tamm plasmon modes, Appl. Phys. Lett. 100,
232111 (2012)
[3] C. Symonds et al., Emission of Tamm plasmon/exciton polaritons, Appl. Phys. Lett. 95, 151114 (2009)
[4] G. Lheureux et al., Polarization-Controlled Confined Tamm Plasmon Lasers, ACS Photonics 2, 842 (2015)
[5] B.I. Afinogenov et al., Observation of hybrid state of Tamm and surface plasmon-polaritons in onedimensional photonic crystals, Appl. Phys. Lett. 103, 061112 (2013)
Terahertz emission from multiple-microcavity exciton-polariton lasers
S. Hupperta, O. Lafonta, E. Baudina, J. Tignona, R. Ferreiraa
a
Laboratoire Pierre Aigrain, Département de physique de l’ENS, École normale supérieure,
PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités,
UPMC Univ. Paris 06, CNRS, 75005 Paris, France
* Corresponding author: [email protected]
The development of efficient coherent sources for terahertz (THz) emission is a subject of intense activity
for both applied and fundamental research. Various strategies have been exploited, in particular using nonlinear
optical effects such as frequency multiplication in nonlinear diodes or difference frequency generation from
infrared or optical laser sources. Recently, it was suggested that exciton-polariton lasers could be efficient tools
for THz generation [1–3]. The strong coupling between quantum well excitons and photons in a semiconductor
microcavity produces mixed light-matter states called exciton-polaritons. Under intense optical excitation, the
polariton lasing regime is reached and the polariton population of the lower branch becomes extremely high in
the vicinity of the zero momentum state [4]. Radiative transitions between the upper and the lower polariton
branches are strongly favored in this regime due to final-state stimulation effect. Furthermore, the Rabi splitting
between the two branches is typically several meV, which makes polariton lasers very promising for THz
generation (1 THz corresponds to 4.1 meV). However, for centrosymmetric quantum well structures, the dipole
matrix element between upper and lower polaritons is zero and the THz transition is symmetry forbidden. In
order to allow for THz emission, it was suggested to break the centrosymmetry by applying an electric field [1],
to populate the 1p–exciton state with two-photon pumping [2] or to realize structures in which 1s and 2p
excitons are resonant and hybridize [5].
The present work focuses on using a quantum well with intrinsically asymmetric design and shows that the
THz transition becomes allowed in such a structure [3]. This configuration provides efficient optical pumping of
the upper state and nonzero THz emission probability to the lower state, without complexifying the experimental
setup. The main obstacle to the THz emission is the existence of nonradiative scattering processes which deplete
the upper polariton state very efficiently. Following Diederichs et al. [6 ,7], we suggest a device using multiple
microcavities in order to hinder nonradiative scattering. We compare the scattering rates associated with three
different mechanisms in single and in double microcavities, and we show that these rates can be reduced by four
orders of magnitude in the latter configuration, while the THz emission rate is only weakly affected. In that case,
the device efficiency is no longer limited by nonradiative scattering but only by the radiative decay of injected
polaritons. The conversion ratio of polaritons into THz photons is predicted to reach 10-3, which is promising for
THz technologies.
References
[1] K. V. Kavokin, M. A. Kaliteevski, R. A. Abram, A. V. Kavokin, S. Sharkova, and I. A. Shelykh, Appl. Phys.
Lett. 97, 201111 (2010).
[2] A. V. Kavokin, I. A. Shelykh, T. Taylor, and M. M. Glazov, Phys. Rev. Lett. 108, 197401 (2012).
[3] S. De Liberato, C. Ciuti, and C. C. Phillips, Phys. Rev. B 87, 241304 (2013).
[4] J. Kasprzak et al., Nature 443, 409 (2006).
[5] T. C. H. Liew, M. M. Glazov, K. V. Kavokin, I. A. Shelykh, M. A. Kaliteevski, and A. V. Kavokin, Phys.
Rev. Lett. 110, 047402 (2013).
[6] C. Diederichs and J. Tignon, Appl. Phys. Lett. 87, 251107 (2005).
[7] C. Diederichs, J. Tignon, G. Dasbach, C. Ciuti, A. Lemaitre, J. Bloch, P. Roussignol, and C. Delalande,
Nature 440, 904 (2006).
THz microfluidic sensor chip
Masayoshi Tonouchi*
Institute of Laser Engineering, Osaka University
* Corresponding author: [email protected]
In this study, we proposed and developed the THz-µTAS that consists of the microfluidic channel and
meta-atoms for quantitative and sensitive measurement of trace amounts of liquid. A femtosecond laser beam is
focused onto a nonlinear optical crystal (NLOC) and generates THz waves locally via optical rectification. The
generated THz waves transmit through a sample that is set in the vicinity of the THz source and are detected at a
photoconductive (PC) antenna in the far-field method. Therefore, THz-TDS and imaging of samples with sub
wavelength scale size can be realized[1,2]. The system has a potential for the measurement of trace amount of
liquid.. The NLCO crystal is coupled to a few THz meta-atoms to enhance the sensitivity. We succeeded in
detecting the amount of minerals in the mineral water with the sensitivity of less than 60 femto mol. The
THz- TAS can be worked as one of sensitive THz chip devices and could be contributed for micro analytical
technology in biological and medical fields.
Fig. 1: A schematic drawing of THz- TAS
References
[1] K. Serita, S. Mizuno, H. Murakami, I. Kawayama, Y. Takahashi, M. Yoshimura, Y. Mori, and M. Tonouchi,
“Scanning laser terahertz near-field imaging system,” Opt. Express 20, 12959(2012).
[2] H. Murakami, K.Serita, E. Matusda, I. Kawayama, and M. Tonouchi, “Scanning laser terahertz imaging
system,” J. Phys. D: Appl. Phys. 47, 374007 (2014).
Coherent absorption of light by graphene and other plasmonic structures
A. Tredicucci a,b,c *
a
Dipartimento di Fisica “E. Fermi,” Università di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
b
Fondazione Bruno Kessler (FBK), Via Sommarive 18, 38123 Povo, Trento, Italy
c
NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
* Corresponding author: [email protected]
The light absorption properties of a system are typically considered an intrinsic material feature, mostly
determined by its dielectric constant, thickness, etc. It has recently been shown, however, that full interferometric
control of absorption can instead be accomplished by varying the relative phase of two coherent optical fields.
Depending on the phase relation, the system can become totally opaque (coherent perfect absorption – CPA) or
tuned to complete transparency (coherent perfect transparency – CPT).
These phenomena are now starting to be widely investigated at a fundamental level (CPA is actually
considered the time-reversed process of lasing) and in view of innovative applications in plasmonics, or even in
diagnostics and imaging techniques where the high selectivity provided by the interferometric absorption control
could prove highly beneficial. Here I will discuss CPA and CPT in devices relying on polaritonic resonances,
properly engineered in a metal metamaterial on top of a quantum well semiconductor heterostructure. Using
diffraction gratings on Gallium Arsenide suspended membranes, "two-beam absorbance" measurements in a
counter-propagating Mach Zehnder geometry reveal the absorption phase modulation. Furthermore, we report on
experiments of coherent absorption on turbostratic multilayer graphene grown on silicon carbide substrate. From
the analysis of the experimental data, the graphene conductance G can be deduced independently of the substrate
and, thus, the number of layers NG can be directly quantified.
For a proper interpretation of the experimental results, a general theory of CPA in linear two-port systems is
constructed, without any symmetry requirements except for reciprocity; it demonstrates that optical absorption
describes an ellipse as function of the difference between the intensities of the incident beams. The model is
interpreted in the polariton case within a standard coupled-mode theory, and allows casting the graphene results
in the more general landscape of optically conductive surfaces.
References
[1] Baldacci, L., Zanotto, S., Biasiol, G., Sorba, L., and Tredicucci, A., “Interferometric control of absorption in
thin plasmonic metamaterials: general two port theory and broadband operation,” Opt. Express, Vol. 23, No. 17,
9202–9210, 2014.
[2] Zanotto, S., Mezzapesa, F. P., Bianco, F., Biasiol, G., Baldacci, L., Vitiello, M. S., Sorba, L., Colombelli, R.,
and Tredicucci, A., “Perfect energy-feeding into strongly coupled systems and interferometric control of
polariton absorption,” Nature Phys., Vol. 10, No. 11, 830–834, 2014.
[3] Zanotto, S., Bianco, F., Miseikis, V., Convertino, D., Coletti, C., and Tredicucci, A., “Coherent absorption of
light by graphene and other optically conducting surfaces in realistic on-substrate configurations,” APL
Photonics, Vol. 2, No. 1, 016101, 2017.
THz photonic and nanoelectronics deviced exploiting 2D materials
Miriam Serena Vitiello
NEST, CNR-NANO, Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy
Bi-dimensional nano-materials and related heterostructures are establishing themselves as new
photonic and electronic materials with huge potential in a variety of applications ranging from
saturable absorbers to optical modulators, from optical communication components when placed on
chip with flat integrated optical circuits to spintronics, from near field components to highresolution sensing and fast tomography. Their peculiar band-structure and electron transport
characteristics, which can be easily manipulated via layer thickness control, suggest they could also
form the basis for a new generation of high-performance devices operating in the Terahertz
frequency range (1-10 THz) of the electromagnetic spectrum. This paper will review our latest
achievements in THz photonic and nano electronic devices based on 2D nano-materials and discuss
future perspectives of this rapidly developing research field. Room temperature, sensitive, high-speed bolometers using doubly clamped
microelectromechanical resonators
Ya Zhanga*, Suguru Hosonoa, Naomi Nagaia and Kazuhiko Hirakawaa,b
a
Center for Photonics Electronics Convergence, Institute of Industrial Science, University of Tokyo, 4-6-1
Komaba, Meguro-ku, Tokyo 153-8505, Japan
b
Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo
153-8505, Japan
* Corresponding author: [email protected]
Microelectromechanical system (MEMS)-based resonators are very attractive for sensing applications owing
to their high sensitivities. High quality (Q)-factors of MEMS resonators lead to excellent sensitivities in
detecting changes in the resonance frequencies. Recently, we proposed an uncooled, sensitive bolometer by
using a MEMS resonator1. Fig. 1(a) shows the wafer structure2 and Fig. 1(b) shows a schematic illustration of a
MEMS resonator, which can be excited and detected both by piezoelectric effect.2 The device had an oscillation
frequency of ~380 kHz and a Q-factor of ~ 3000, measured in a vacuum level of 10-4 torr at 300 K. We deposited
a 10-nm NiCr layer on the MEMS beam surface as a THz absorber and also as a heater for the calibration of the
sensitivity of the detector. When a heating power is applied to the NiCr film, a thermal stress is generated in the
beam, which reduces the resonance frequency, as shown in Fig. 1(c). We have estimated the noise equivalent
power (NEP) of the resonator to be below 20 pW/Hz1/2, which is very promising for realizing high sensitivity
terahertz (THz) detection at room temperature.
Furthermore, we have performed frequency modulation (FM) detection for the fast operation of MEMS
bolometers. In a conventional “slope detection” scheme, the shift in the resonance frequency is determined by
the change in the oscillation amplitude, which limits the operation bandwidth to be ~f/Q (~100 Hz for the present
device). In contrast, in the FM detection scheme, the resonator works in a self-sustained mode with a constant
amplitude by using a feedback circuit. The FM detection scheme allows a heat detecting speed which is not
limited by the Q-factors, allowing a fast THz detection in the order of several kHz. Fig.1 (d) shows the
normalized thermal responses in two different schemes (slope detection and FM detection) as a function fo the
heat modulation frequency. As seen, the heat detecting bandwidth for the FM detection is ~50 times of that for
the slope detection scheme, demonstrating the fast THz bolometric detection by MEMS resonators.
Fig. 1 (a) Schematic cross section of the wafer structure. (b) Schematic sample structure of the MEMS resonator
(120L×30W×1.5H μm3). (b) Shift in the resonance frequency with increasing heating power. (c) Normalized
thermal responses for the slope and FM detection schemes as a function of the heat modulation frequency.
References
[1] Y. Zhang, et al., Appl. Phys. Lett. 108 (16), 163503 (2016).
[2] I. Mahboob and H. Yamaguchi, Nat. Nanotechno. 3, 275 (2008).