Content
======================================================================================
======================================================================================
Sunday April 19, 2015
======================================================================================
======================================================================================
Sun 12:00 - 14:30 Arrival and Registration
======================================================================================
======================================================================================
Sun 14:30 - 15:25 Welcome Reception
======================================================================================
======================================================================================
Sun 15:25 -15:40
======================================================================================
Regine Frank
Institute of Theoretical Physics, Optics and Photonics, Eberhard-Karls University of Tübingen, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Welcome
======================================================================================
======================================================================================
Sun 15:40 - 16:00
======================================================================================
Ernst Dreisigacker
Wilhelm and Else Heraeus Foundation, Hanau, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Welcome
======================================================================================
======================================================================================
Sun 16:00 - 17:30
======================================================================================
Dan T. Kulp
American Physical Society, 1 Research Road, Ridge, NY USA
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Physical Review and You
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The Physical Review family of journals has a long and rich history. Since its establishment in 1893, and under the guidance of the American Physical Society, it has grown and expanded into a broad, international family of journals covering all fields of physics. We will briefly discuss the history and growth of the journals before jumping into the current state of publishing, including the peer-review process and the roles played by authors, referees, and editors; and the business of publishing, including the expenses and the effect of open access.
======================================================================================
======================================================================================
Sun 17:30 - 19:00
======================================================================================
Poster-Introduction: Show and Tell
======================================================================================
======================================================================================
Sun 19:00 Dinner and informal get-together
======================================================================================
======================================================================================
Monday April 20, 2015
======================================================================================
======================================================================================
Mo 8:30 - 9:25
======================================================================================
Sven Höfling
Technische Physik and Wilhelm-Conrad-Röntgen Research Center for Complex Material Systems, Universität Würzburg, D-97074
Würzburg, Am Hubland, Germany
SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS,UK
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Polariton condensation in deep traps and lattices
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Exciton polaritons are an ideal system to study collective behavior of macroscopic coherent quantum states in a solid state environment as they fulfill a range of important prerequisites. The possibility to engineer polariton trapping potentials has triggered the interest in using polaritonic systems to simulate complex many-body phenomena, such as the physics of high-temperature superconductors, graphene, or frustrated spin lattices. We employ a technology that enables deep (several meV), potentially tunable trapping in any 2D geometry without a
ecting the favorable polariton characteristics. The traps are based on a locally elongated microcavity which can be formed by standard lithography [1, 2] We observe polariton condensation under non-resonant pumping in single traps and photonic crystal lattice arrays. In the latter structures, we observe pronounced energy bands, complete band gaps, and the spontaneous condensation at the M-point of the Brillouin zone.
[1] O. El Daif et al., Appl. Phys. Lett. 88, 061105 (2006).
[2] K. Winkler et al., New J. Phys 17, 023001 (2015).
======================================================================================
======================================================================================
Mon 9:25 - 10:20
======================================================================================
Andreas Lubatsch
Electrical Engineering, Precision Engineering, Information Technology,
Georg-Simon-Ohm University of Applied Sciences,
90489 Nürnberg, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Optical Excitations in Materials with Strong Electronic Correlations -
A Non-Equilibrium Many Body Approach
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
A dynamical mean field theory (DMFT) is presented which is generalized to situations where the considered system is out of thermodynamical equilibrium. The nonequilibrium DMFT derives properties such as electronic density of states (LDOS) and occupation numbers of the optically driven system. It fully characterizes the system in its time dependent state. Results for the metallic pseudogap phase display a strongly increased quantum coherence at intersections of photoinduced sidebands. This leads to a revival of the manyparticle resonance at the Fermi energy. Large U results demonstrate that the system exhibits an insulatormetal transition as the frequency of the external field is increased and exceeds the gap. Also it is demonstrated, how such a setup may be employed in order to realize alloptical switching processes in various materials.
Furthermore, such externally pumped interacting electronic systems are coupled to quantized photonic modes as observed in wave guides or stacked composite systems.
Extraordinary effects on the electronic lifetime are discussed with regard to potential applications.
A. Lubatsch, R. Frank, arxiv.org/abs/1504.00949
======================================================================================
======================================================================================
Mon 10:20 -10:40 Coffee
======================================================================================
======================================================================================
Mon 10:40 - 11:35
======================================================================================
Bart v. Tiggelen
Laboratoire de Physique et Modélisation des Milieux Condensés (LPMMC), CNRS, Université Joseph Fourier, Grenoble, France
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Casimir Momentum in Complex Media
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Casimir energy refers to the electromagnetic energy that quantum mechanics imposes to exist even
in a fully empty space at temperature zero. In the presence of polarizable matter it gives rise to
many fundamental phenomena in physics such as Lamb shift and Van de Waals forces, and maybe
even the cosmological constant. In the conventional picture- either with or without matter - the
expectation value of the electromagnetic momentum, < E x B > , called Casimir momentum
vanishes. This may be physically obvious in “simple media”, when < E x B > is directly
proportional to the energy flow < E x H > which arguably vanishes unconditionally in
thermodynamic equilibrium, but as soon as symmetries are broken (P, and T in particular) the
question whether Casimir momentum can exist appears and turns out nontrivial.
The momentum of classical electromagnetic waves has been the subject of a longstanding
controversy. In the presence of both an external electric E0 and magnetic field B0 the so-called
Nelson version (our favorite) predicts a momentum α(0) E0 x B0 which results in the “Abraham
force” F= α(0) d/dt( E0 x B0). We have measured this very tiny force in atomic gases and also
searched – in vain - for possible deviations from the (Nelson version of) classical theory. In the
QED picture in fact three momenta appear that are all different: kinetic momentum (related to force
and thus observable), canonical momentum (conjugate to position operator and subject to gauge
fields), and pseudo-momentum (which commutes with Hamiltonian and is thus conserved). We
have developed a nonrelativistic QED theory for the electromagnetic momentum for simple objects
coupled to the quantum vacuum. It produces the Abraham force with a QED correction. For the
hydrogen atom the relative correction is equal to -0.12 α2
, nonzero, yet very small. We speculate
that for other (hydrogen-type) atoms the correction scales as (Zα)2
. Important to note is that the
classical theory diverges in the infrared, and with some cut-off much higher QED corrections are
proposed, that would have been within our experimental reach. In the fully QED theory, this
divergence disappears after mass renormalization.
Does Casimir momentum exist with only a magnetic field? If the matter is optically active, with
β(0) the static rotatory factor, a momentum β(0)/α(0) eB0 could exist in view of its correct PCT
symmetry and its correct dimension. However, such a momentum does not emerge from classical
electrodynamics. We have developed a QED theory for a chiral, anisotropic, harmonic oscillator
subject to a magnetic field. This theory, free of divergence, predicts a Casimir momentum
proportional to -(α/4π) β(0)/α(0) eB0 . Observation of this momentum is a next challenge. For a
typical chiral compound C8H18O we predict velocities P/M = 0. 5 nm/sec at 10 Teslas.
======================================================================================
======================================================================================
Mon 11:35 - 12:30
======================================================================================
Klaus Richter
Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Many-Particle Interference Phenomena
in Fock Space
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Wave interference effects in quantum transport through disordered or complex chaotic systems have mainly been treated on the level of single-particle dynamics.
The generalization to interacting many-body systems remains to be one of the major challenges in this field. I will consider many-body quantum interference from the perspective of interfering quantum paths in Fock space and review a novel semiclassical approach to the many-body Feynman propagator for bosons[1] and fermions[2]. This allows us to address a variety of quantum effects such as coherent backscattering [1] and spin echo [3] in Fock space of interacting particles, as well as phenomena arising from indistinguishability of bosons in complex scattering systems, such as boson sampling [4,5].
[1] T. Engl, J. Dujardin, A. Argüelles, P. Schlagheck, K. Richter, J.-D. Urbina, Phys. Rev. Lett. 112, 140403 (2014)
[2] T. Engl, P. Plößl, J. Urbina, K. Richter, Theoretical Chemistry Accounts 133, 1563 (2014)
[3] T. Engl, J.-D. Urbina, K. Richter, arXiv:1409.5684 [cond-mat] (2014)
[4] J.-D. Urbina, J. Kuipers, Q. Hummel, K. Richter, arXiv:1409.1558 [quant-ph] (2014)
[5] M. Walschaers, J. Kuipers, J.-D. Urbina, K. Mayer, M. Tichy, K. Richter, A. Buchleitner, arXiv:1410.8547 [quant-phys] (2014)
======================================================================================
======================================================================================
Mon 12:30 - 13:00
======================================================================================
Alex Edelman
University of Chicago, USA
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Quantum Melting in a Polariton Lattice
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
We study a generalized Dicke model of lattice polaritons, with a pair-potential interaction between excited states of the spin component, in the functional integral formalism. Even considering only zero-temperature equilibrium effects with a uniform photon field, there is a rich phase diagram as a function of light-matter coupling, which includes spatially ordered and superfluid phases. Depending sensitively on the form of the potential, the interaction may induce an instability in the sound mode of the polariton condensate, or destroy the condensate altogether. Zero-temperature fluctuations may likewise melt the spatially ordered phases. We consider implications for cold-atom experiments with tunable interactions, as well as interacting exciton-polaritons accessible in the solid state.
======================================================================================
======================================================================================
Mon 13:00 -14:30 Lunch
======================================================================================
======================================================================================
Mon 14:30 - 15:25
======================================================================================
Peter B. Littlewood
University of Chicago, Chicago and Argonne National Laboratory, Argonne IL USA
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Polaritons with localized atomic states
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Cavity polaritons in semiconductors have become an interesting laboratory to study the development of coherence in light-matter systems. Much of the work to date has focused on III-V and II-VI systems where the interaction between light and electron-hole pairs can be strong, but the excitons are weakly interacting both with each other and with other excitations in the system. We consider two systems where this condition is relaxed. In molecular solids, Frenkel excitons can have strong interactions with local phonon modes, and this dressing by vibrational modes can change the phase diagram and spectrum of excitations[1]. In atomic systems where the excited state is a highly excited Rydberg atom, there are now long-range repulsive interactions between excitons, in addition to the photon-mediated hopping. In this system, it has been proposed that there is a phase transition from polariton solid to polariton superfluid, so far treated only at the mean field level [2].
[1] Justyna A. Cwik, Sahinur Reja, Peter B. Littlewood, Jonathan Keeling, EPL 105 47009 (2014)
[2] Xue-Feng Zhang, Qing Sun, Yu-Chuan Wen, Wu-Ming Liu, Sebastian Eggert, and An-Chun Ji, Phys. Rev. Lett. 110, 090402 (2013)
======================================================================================
======================================================================================
Mon 15:25 - 16:20
======================================================================================
Mordechai (Moti) Segev
Technion – Israel Institute of Technology, Haifa, Israel
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Exquisite Disorder
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
I will review the recent progress on the propagation of waves in disordered photonic systems, with an emphasis on new concepts such as photonic Floquet topological insulators [1] and hyper-transport in systems with evolving disorder [2].
[1] M.C. Rechtsman et al., Nature 496, 196 (2013)
[2] L. Levi et al., Nature Physics 8, 912 (2012)
======================================================================================
======================================================================================
Mon 16:20 - 16:40 Coffee
======================================================================================
======================================================================================
Mon 16:40 - 19:00
======================================================================================
Poster-Session
======================================================================================
======================================================================================
Mon 19:00 - 24:00 WE-Heraeus Buffet
======================================================================================
======================================================================================
Tuesday April 21, 2015
======================================================================================
======================================================================================
Tue 8:30 - 9:25
======================================================================================
Shmuel Fishman
Physics Department, Israel Institute of Technology, Technion Haifa, Israel
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Dynamics in potentials which are random both in
space and time
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
In presence of potentials that are random both in space and time, hyper-transport,
Namely spreading that is faster than ballistic, was found for some systems.
Classification into universality classes of transport in such systems will be presented.
Novel numerical methods to test predictions for such and similar problems will be
presented as well. These may be useful for other systems modeled by differential
equations with time dependent coefficients, including the situation when the
coefficients oscillate rapidly. The work was motivated by experiments in optics
performed by the group of Professor Moti Segev at the Technion.
======================================================================================
======================================================================================
Tue 9:25 - 10:20
======================================================================================
Allard P. Mosk
Complex Photonic Systems (COPS), Dept. TNW and MESA+ Institute for Nanotechnology, University of Twente
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Shaped wavefronts and speckle correlations –
A digital window through opaque media
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Random scattering of light, which takes place in paper, paint and biological tissue is an obstacle to imaging and focusing of light and thus hampers many applications. At the same time scattering is a phenomenon of basic physical interest as it allows the study of interference effects such as Anderson localization, open transport channels and speckle correlations [1].
Propagation of laser light in scattering media can be controlled by shaping the incident wavefront using the massive number of degrees of freedom offered by digital spatial light modulators. Wavefront shaping methods in scattering media have given rise to a new wave of fundamental studies of light propagation as well as new modalities of imaging and focusing of scattered light. The resolution of this focusing can exceed that of conventional focusing optics.
Recently we demonstrated that speckle correlations enable non-invasive fluorescence imaging through strongly scattering layers, without the need of prior calibration. The same principles allow for high-resolution imaging through scattering lenses made of high-index materials, allowing wide-field speckle-illumination microscopy with a resolution approaching 110 nm [2].
Finally, non-imaging applications of wavefront-shaped scattered light are emerging in the context of lighting, cryptography and security [3].
[1] A. P. Mosk, A. Lagendijk, G. Lerosey, and M. Fink, Controlling waves in space and time for imaging and focusing in complex media, Nat. Photon., 6, 283-292, 2012.
[2] H. Yilmaz, E. G. van Putten, J. Bertolotti, A. Lagendijk, W. L. Vos, and A. P. Mosk, Exploiting speckle correlations to improve the resolution of wide-field fluorescence microscopy, ArXiv preprint 1410.2079 (2014).
[3] S. A. Goorden, M. Horstmann, A. P. Mosk, B. Skoric, and P. W. H. Pinkse, Quantum-secure authentication of a physical unclonable key, Optica 1, 421-424 (2014).
======================================================================================
======================================================================================
Tue 10:20 - 10:40 Coffee
======================================================================================
======================================================================================
Tue 10:40 - 11:35
======================================================================================
Willem L. Vos
Complex Photonic Systems (COPS), University of Twente, The Netherlands
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Finite-size scaling of the density of states in a 3D photonic band gap
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The central concept of a bandgap – both electronic or photonic - pertains to infinite systems (L ) only. In contrast, experiments and applications are obviously made with real and finite crystals [1,2], which begs the question: How fast does the density of states (DOS) in the band gap of a finite-crystal approach the infinite-crystal limit? In other words: what is the scaling behavior of the DOS?
Scheme of how to probe the DOS in the band gap of a finite crystal by local probes. Quantum light emitters (yellow spheres) embedded in a finite photonic band gap crystal (square) experience the local density of states (LDOS) as the density of vacuum fluctuations (red wavelets). By averaging over many emitters throughout the crystal, we probe an average LDOS that represents the DOS of the finite crystal.
We exploit a well-known effect in cavity quantum electrodynamics (QED): the density of photonic states plays an essential role
in spontaneous emission of a quantum emitter. We study the scaling behavior of the photonic density of states for a sample that has a full 3D bandgap. We probe a position averaged local density of states that represents the DOS of the finite crystal and converges to the infinite-crystal limit of the DOS. We support our observations by a new theory that introduces finite-size effects into the DOS of an infinite system. Our study provides a first ever design rule for the usage of vanishing density of states, notably to cavity QED, quantum information processing, and Anderson localization.
While the (L)DOS is usually associated with cavity QED and quantum emitters, we note that the LDOS also plays a surprising role in non-linear optics [3]. Finally, we recently found a curious inversion effect of a photonic gap on atomic dispersion [4].
[1] M.D. Leistikow, A.P. Mosk, E. Yeganegi, S.R. Huisman, A. Lagendijk & W.L. Vos, PRL 107, 193903 (2011).
[2] E. Yeganegi, A. Lagendijk, A.P. Mosk & W.L. Vos, PRB 89, 045123 (2014)
[3] E. Yüce, G. Ctistis, J. Claudon, J.-M. Gérard & W.L. Vos, arXiv:1406.3586 (2014)
[4] P.J. Harding, P.W.H. Pinkse, A.P. Mosk & W.L. Vos, PRB 91, 045123 (2015)
======================================================================================
======================================================================================
Tue 11:35 - 12:30
======================================================================================
Kathy Lüdge
Fachbereich Physik, Freie Universität Berlin, Germany
Institut für Theoretische Physik, Technische Universität Berlin, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Nonlinear performance of integrated devices with quantum-dot semiconductor amplifiers and lasers
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Regarding the still growing demands for fast and efficient photonic devices within the telecommunication area, we theoretically investigate semiconductor quantum-dot laser and amplifier structures. The aim is to use semi-classical models that are sophisticated enough to yield reliable quantitative results, while they are still easy enough for analytic treatment to enable prediction of optimized devices.
At first, amplifiers, which are essential devices for compensating losses and extending the reach in fiber-optic networks, will be discussed. Since quantum-dots offer a variety of confined levels and a broad gain spectrum, we show their ability for dual-band operation, i.e. simultaneous amplification of counter-propagating up- and down-stream data signals. Using an optimized delay-differential-equation model, we efficiently simulate the signal propagation and analyze the device performance and the interplay of noise and patterning effects due to coherent light interaction. The signal quality factor of ground and excited state amplification is determined in dependence of pump current and signal power [1]. Simultaneous cross-talk free amplification of two 40 Gbit/s bit streams is possible at an optimum pump current.
Further, the amplitude-phase coupling [2] and two-mode emission of quantum-dot laser structures is investigated in detail. By using our microscopically motivated rate equation model, we focus on the internal charge-carrier scattering processes and predict regions of two-state lasing and ground-state quenching as a function of device temperature, gain, and energy structure [3].
At last, passively mode-locked lasers, i.e. integrated structures of absorber and laser sections, are discussed. The broad gain spectrum of inhomogeneously distributed quantum-dots leads to pulse streams with short pulses. Using an additional optical feedback section, the unwanted fluctuations in the pulse arrival time can be reduced, if the delay time is chosen to be an integer multiple of the internal round trip time. Using two feedback sections even allows for a repetition rate tuning [4].
[1] B. Lingnau, E. Schöll, and K. Lüdge, IEEE Proc. of the 14th international conference on Numerical Simulation of Optoelectronic Devices (2014).
[2] B. Lingnau, W. W. Chow, and K. Lüdge, Opt. Express 22, 4867 (2014)
[3] A. Röhm, B. Lingnau, and K. Lüdge, IEEE J. Quantum Electron. 5, (2015)
[4] C. Otto, L. Jaurigue, E. Schöll, and K. Lüdge, IEEE Photonics Journal 6, 1501814 (2014)
======================================================================================
======================================================================================
Tue 12:30 - 13:00
======================================================================================
Georgios Ctistis
University of Twente,Complex Photonic Systems (COPS),
Saxion University of Applied Sciences, Twente, The Netherlands
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Dynamics of light and matter in ultrafast-switched semiconductor microcavities
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
We present time dependent differential reflectivity measurements of a GaAs/AlAs planar microcavity over a broad frequency range, switched by free carrier excitation. We observe that the switching dynamics shows a spectral dependence. To accurately describe and understand this behavior we propose a model beyond the existing single population model.
======================================================================================
======================================================================================
Tue 13:00 -14:30 Lunch
======================================================================================
======================================================================================
Tue 14:30 - 15:25
======================================================================================
Sergej Flach
New Zealand Institute for Advanced Study, Massey University, Auckland, New Zealand
Center for Theoretical Physics of Complex Systems, Institute for Basic Science, Daejeon, Korea
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Quantum chaotic subdiffusion in random potentials
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Two interacting particles (TIP) in a disordered chain propagate beyond the single particle localization length ξ1 up to a scale ξ2 > ξ1. An initially strongly localized TIP state expands almost ballistically up to ξ1. The expansion of the TIP wave function beyond the distance ξ1 ≫ 1 is governed by highly connected Fock states in the space of noninteracting eigenfunctions. The resulting dynamics is subdiffusive, and the second moment grows as m2 ∼ t1/2 [1], precisely as in the strong chaos regime for corresponding nonlinear wave equations [2–7]. This surprising outcome stems from the huge Fock connectivity and resulting quantum chaos. The TIP expansion finally slows down towards a complete halt – in contrast to the nonlinear case.
[1] M. V. Ivanchenko, T. V. Laptyeva and S. Flach, Phys. Rev. B Rapid Comm. 89, 060301 (2014)
[2] S. Flach, D. O. Krimer and Ch. Skokos, Phys. Rev. Lett. 102, 024101 (2009)
[3] S. Flach, Chem. Phys. 375, 548 (2010)
[4] T.V. Laptyeva et al, EPL 91, 30001 (2010)
[5] J.D. Bodyfelt et al, Phys. Rev. E 84, 016205 (2011)
[6] S. Flach, arXiv:1405.1122 (2014)
[7] T. V. Laptyeva, M. V. Ivanchenko and S. Flach, Topical Review, J. Phys. A: Math. Theor. 47, 493001 (2014)
======================================================================================
======================================================================================
Tue 15:25 - 16:20
======================================================================================
Cornelia Denz
AG Nichtlineare Photonik, Istitut für Angewandte Physik, Universität Münster, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Biomimetic flower lattices - light in complex, spiral, and disordered photonic refractive index structures
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Photon transport can be effectively controlled by tailoring the wave vector spectrum of artificial structured photonic refractive index media. Whereas ordered photonic lattices with discrete k-vector spectra as photonic graphene, quasicrystals, or com-plex elliptical or hyperbolical lattices have proven to create functional band gap ma-terials that effectively mold the flow of light, disordered lattices with a random k-vector distributions are known to create diffusive transport. Weak interaction may lead to coherent backscattering, and strong interaction to Anderson localization. However, ubiquitous methods to control randomness are still lacking.
In our contribution, we will deliberately tailor disorder in photonic lattices by introduc-ing signatures of order, thereby adapting the underlying transport mechanisms. Ex-amples are disordered lattices with defined surfaces, interfaces, or islands of regu-larity, lattices with random band gaps, and deterministic aperiodic lattices with local or cluster-like spectra. The latter are omnipresent in nature. The Fibonacci sequence, associated with the golden ratio, and its emergent patterns include flower petals, seed heads, shells, and DNA molecules. 2d vortices, spirals or 3d helices are the basis of these structures. We present techniques to realize such structures in photo-refractive media, e.g. based on a spatially resolved scanning induction with non-diffracting Bessel beams as the fundamental entities. We demonstrate the potential of this approach to realize spatially extended Vogel spirals [1], Fibonacci lattices [2], and clusters of coupled waveguides [3], and discuss light propagation scenarios.
Besides scalar singularities in the form of optical phase vortices, vectorial singulari-ties can be created in the transverse plane of light containing a spatially inhomoge-neous distribution of polarization. We present the potential of our holographic ap-proach [4] to generate classical radially and azimuthally polarized beams, higher order vectorial singularities, and complex singularity lattices forming “flower gar-dens” and “spider webs”.
[1] F. Diebel, P. Rose, M. Boguslawski, C. Denz, Appl. Phys. Lett. 104, 191101 (2014)
[2] M. Boguslawski, N. M. Lucić, D. V. Timotijević, C. Denz, D. M. Jović- Savić, arXiv:1501.04479 (2015).
[3] F. Diebel, D. Leykam, M. Boguslawski, P. Rose, C. Denz, A. Desyatnikov, Appl. Phys. Lett. 104, 261111 (2014).
[4] C. Alpmann, C. Schlickriede, E. Otte, C. Denz, submitted (2015).
======================================================================================
======================================================================================
Tue 16:20 - 16:40 Coffee
======================================================================================
======================================================================================
Tue 16:40 - 17:30
======================================================================================
Thierry Giamarchi
DPMC, University of Geneva 24, Quai Ernest Ansermet, 1211 Geneva, Switzerland
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Transport in low dimensional quantum systems
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Low dimensional quantum systems, in particular in zero or one dimension present properties markedly different than their higher dimensional counterparts. In one dimensional quantum fluids, generically described by the concept of Tomonaga-Luttinger liquids (TLL), the absence of individual quasiparticles affects drastically the transport properties. I will discuss results on transport in such systems both for the case of quantum point contacts, for which a full non-equilibrium solution can be found and for TLL in particular in the case of disorder. I will discuss these results in the light of recent experiments both in condensed matter systems and cold atomic gases. In particular in cold atomic gases both one dimensional disordered structures and quantum point contacts could be recently realized providing controlled experimental situations corresponding to the above-mentioned theoretical situations.
======================================================================================
======================================================================================
Tue 17:35 - 18:30
======================================================================================
Giovanni Modugno
LENS, University of Florence, Italy
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Measurement of the mobility edge for 3D Anderson localization with ultracold atoms
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Anderson localization is a universal phenomenon affecting quantum particles in a disordered environment. In three spatial dimensions, theory predicts a quantum phase transition from localization to diffusion at a critical energy, the mobility edge, which depends on the disorder strength. Although it has been recognized already long ago as a prominent feature of disordered systems, so far the mobility edge could not be measured in any physical system.
I will report on the measurement of the mobility edge for ultracold atoms in a disordered potential created by laser speckles. We are able to measure the mobility edge in a range of disorder strengths sufficiently large to explore both regimes where the spatial correlations of the disorder are relevant or not relevant. The precise control over the atomic system allows now a close experiment-theory comparison, and is a prerequisite to study the even more challenging problem of disorder and interactions.
G. Semeghini, M. Landini, P. Castilho, S. Roy, G. Spagnolli, A. Trenkwalder, M. Fattori, M. Inguscio and G. Modugno, arXiv:1404.3528.
======================================================================================
======================================================================================
Tue 18:30 - 19:00
======================================================================================
Lorenzo Cortese
Lens - European Laboratory for Non-Linear Spectroscopy, Florence, Italy
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Lessons from nature: how white beetles optimise light scattering
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
A bright white colour usually arises from light scattering through thick, high-refractive-index, random systems. The extremely bright whiteness shown by the Cyphochilus beetles is instead generated by multiple scattering of light inside the ultra-thin low-refractive-index scales that cover its body. The intra scale structure is characterized by a dense, nanostructured anisotropic network of chitin filaments, which is optimised (during million of years of evolution) to increase the total reflectance, and thus the bright appearance of the beetle, employing as less material as possible.
======================================================================================
======================================================================================
Tue 19:00 Dinner and informal get-together
======================================================================================
======================================================================================
Wednesday April 22, 2015
======================================================================================
======================================================================================
Wed 8:30 - 9:25
======================================================================================
Boris Shapiro
Technion - Israel Institute of Technology, Haifa, Israel
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
PT-symmetric Magnetic Structures
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
We investigate PT–symmetric magnetic nanostructures and show that their magnetic moments can exhibit a new type of dynamics. Using the simplest possible set-up, consisting of two coupled ferromagnetic films, one with loss and the other with a balanced amount of gain, we demonstrate the existence of PT-symmetry breaking when both the eigenfrequencies and the eigenvectors become degenerate. Below the critical point the frequency spectrum is real, indicating stable dynamics, while above this point it becomes complex, signaling unstable dynamics which is only stabilized by nonlinear effects.
======================================================================================
======================================================================================
Wed 9:25 - 10:25
======================================================================================
Georg v. Freymann
Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Fraunhofer Institute for Physical Measurement Techniques, 67663 Kaiserslautern, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Transverse mode localization in 3D deterministic aperiodic structures
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Introducing tailored disorder into three-dimensional photonic structures allows for studying the disorder-related change of the underlying transport mechanisms. Here, we introduce deterministic aperiodic disorder in periodic photonic crystals. Deterministic aperiodic structures offer the possibility to reproducibly create specific potential landscapes whose Fourier components are determined by the underlying aperiodic sequence. In accordance with Lebesgue’s spectral theorem the Fibonacci, Thue-Morse and Rudin-Shapiro sequences are examples of the three basic spectral measures, namely pure-point, singularly-continuous and absolutely-continuous, respectively. Especially, the Rudin-Shapiro series is found to be indiscernible from randomly disordered samples concerning their diffraction patterns/properties [1]. Varying the structural parameters, e.g., the lattice spacing, according to the aperiodic sequences allows us to introduce deterministic aperiodic disorder into the photonic crystals [2,3].
Samples are fabricated via direct laser writing in negative-tone photoresist. Using a dip-in lithography approach, samples of considerable height (> 70 unit cells) are prepared with constant high quality throughout the volume. We measure reflectance and transmittance spectra as well as time-resolved photonic transport and correlate the results with mode patterns to deduce the underlying transport mechanism [2]. The different types of aperiodic disorder show characteristic transport properties well reproduced in numerical calculations.
[1] M. Baake and U. Grimm, J. Phys. Conf. Ser. 226, 012023 (2010)
[2] Michael Renner and Georg von Freymann, Advanced Optical Materials 2, 226 (2014)
[3] 3D Photonic Quasicrystals and Deterministic Aperiodic Structures, A. Ledermann, M. Renner, and G. von Freymann, in “Light Localization and Lasing”, Mher Ghulinyan, and Lorenzo Pavesi, editors, Cambridge University Press (2015)
======================================================================================
======================================================================================
Wed 10:20 -10:40 Coffee
======================================================================================
======================================================================================
Wed 10:40 - 11:35
======================================================================================
Georg Maret
Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Nonlinear signatures of Anderson localization of light
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Breakdown of wave transport due to strong disorder is a universal phenomenon
known as Anderson localization. It occurs because of the macroscopic population of
reciprocal multiple scattering paths, which in three dimensional systems happens at a
critical scattering strength given by kl* ~ 1, with k denoting the wave vector and l* the
transport mean free path. A clear experimental signature of the localization transition
is the slowing down of light diffusion revealed by a long time tail of the time resolved
total transmission [1] and a saturation of the spatial intensity profile at the backside of
samples [2]. Both of these signatures consistently show a critical behavior as a
function of kl* with a transition near kl* = 4.
Intensities on the random localized loops are expected to be highly increased relative
to those of a diffusive sample. In order to highlight localized modes of light
experimentally, we exploit the optical nonlinearities of titania (TiO2). Power
dependent and spectrally resolved time of flight distribution measurements in
transmission through slabs of TiO2 powders at various kl* reveal that mostly long
loops are affected by nonlinearities and that the deviations from diffusive transport
observed at long times are due to these localized modes. Our data are a first step in
the experimental investigation of the interplay between non-linear effects and
Anderson localization in 3D.
[1] M. Störzer, P. Gross, C.M. Aegerter and G.Maret
Phys.Rev.Lett. 96, 063904 (2006)
[2] T. Sperling, W. Bührer, C.M. Aegerter and G. Maret,
Nature Photonics 7, 48, (2013)
[3] T. Sperling, W. Bührer, M. Ackermann, C.M. Aegerter and G. Maret,
New Journal of Physics 16, 112001 (2014)
======================================================================================
======================================================================================
Wed 11:35 - 12:30
======================================================================================
Jacopo Bertolotti
Physics and Astronomy Department, University of Exeter, UK
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Non-invasive imaging through opaque scattering layers
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Non-invasive imaging requires the ability to form sharp pictures even when a strongly
scattering material acts as a screen between the object and the detector. Light
scattering scrambles the optical signal, blurring the picture and making direct imaging
impossible [1]. Several approaches, each with their own range of applicability,
advantages and limitations, were proposed and demonstrated in the past. Ranging
from adaptive optics [2], to optical coherence tomography [3], to diffuse tomography
[4], to wavefront-shaping techniques [5].
We have recently demonstrated a novel reference-free imaging method that can
retrieve
the image of a fluorescent object behind a thin layer that scatters all incident
light [6]. The incident laser light is scrambled by a diffuser which transmits negligible
ballistic light. The speckles that hit the object excite fluorescence, that
appear as a diffused blob on the front side of the diffuser. However the optical
memory effect allows deterministic scanning of this overlap when the scattering
layer has a physical thickness that is small compared to the distance to the
object. By varying the incident angle, an angle-dependent intensity is measured
from which the autocorrelation of the object can be extracted. Subsequently
the shape of the object can be retrieved from the autocorrelation.
[1] V. Ntziachristos, Nat. Methods 7, 603 (2010).
[2] J. A. Kubby, “Adaptive Optics for Biological Imaging” (CRC Press 2013).
[3] N. Abramson, Opt. Lett. 3, 121 (1978).
[4] P. den Outer, T, Nieuwenhuizen, and A. Lagendijk, J. Opt. Soc. Am. A 10, 1209
(1993).
[5] I. M. Vellekoop and A. P. Mosk, Opt. Lett. 32, 2309 (2007).
[6] J. Bertolotti, E. G. van Putten, C. Blum,A. Lagendijk, W. L. Vos, and A. P.
Mosk, Nature 491, 232 (2012).
======================================================================================
======================================================================================
Wed 12:30 - 13:00
======================================================================================
Fabrice Mortessagne
Laboratoire de Physique de la Matière Condensée, Université Nice Sophia Antipolis, CNRS Nice, France
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Selective enhancement of topologically induced interface states in a dielectric resonator chain
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The recent realization of topological phases in insulators and superconductors has advanced the search for robust quantum technologies. The prospect to implement the underlying topological features controllably has given incentive to explore optical platforms for analogous realizations. Here we realize a topologically induced defect state in a chain of dielectric microwave resonators and show that the functionality of the system can be enhanced by supplementing topological protection with non-hermitian symmetries that do not have an electronic counterpart. We draw on a characteristic topological feature of the defect state, namely, that it breaks a sublattice symmetry. This isolates the state from losses that respect parity-time symmetry, which enhances its visibility relative to all other states both in the frequency and in the time domain. This mode selection mechanism naturally carries over to a wide range of topological and parity-time symmetric optical platforms, including couplers, rectifiers and lasers.
C. Poli et al., Nat. Commun. 6:6710 doi: 10.1038/ncomms7710 (2015)
======================================================================================
======================================================================================
Wed 13:00 - 14:00 Lunch
======================================================================================
======================================================================================
Wed 14:00 - 24:00 Outing
======================================================================================
======================================================================================
Thursday April 23, 2015
======================================================================================
======================================================================================
Thu 8:30 - 9:25
======================================================================================
Alexander Altland
Institute for Theoretical Physics, University of Cologne, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Topological Kondo Effect
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
In this talk, we will briefly review recent progress in realizing Majorana fermion bound states in condensed matter devices. We will motivate a structure comprising semiconductor quantum wires coupled to a superconductor, and to external leads as the most generic device architecture realizing Majorana fermion transport by current date technology. In the main part of the talk we will discuss how a conspiracy of topological correlations and electrostatic interaction drive such 'Majorana quantum dots' to a fixed point fundamentally different from an ordinary Fermi liquid fixed point. At strong coupling, the system exhibits unconventional transport behavior and non-Fermi liquid correlations which make it distinct from any conventional quantum electronic device. We will close by discussing possible extensions of the elementary Kondo cell to more complex architectures.
======================================================================================
======================================================================================
Thu 9:25 - 10:30
======================================================================================
Laurent Sanchez-Palencia
CNRS and Univ Paris-Saclay, Palaiseau (Paris), France
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Anderson Localization in Disordered and
Quasiperiodic Bose Superfluids
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The dynamics of many-body quantum systems is attracting a growing attention,
motivated by the development of novel devices where parameters can be controlled.
In a disordered environment, the interplay of interactions and localization still poses
challenging questions. Here we discuss collective Anderson localization in disordered
and quasiperiodic Bose superfluids. We show that, although the density background
is extended owing to strong-enough repulsive interactions, the many-body excitations
can be exponentially localized. We develop an analytical approach, which allows us
to derive quantitative predictions, and draw a clear physical picture. We also report
numerical calculations, which support our analysis. The truly disordered and
quasiperiodic cases are discussed and compared.
[1] P. Lugan et al., Phys. Rev. Lett. 99, 180402 (2007).
[2] P. Lugan and L. Sanchez-Palencia, Phys. Rev. A 84, 013612 (2011).
[3] S. Lellouch and L. Sanchez-Palencia, Phys. Rev. A 90, 061602(R) (2014).
======================================================================================
======================================================================================
Thu 10:20 -10:35 Coffee
======================================================================================
======================================================================================
Thu 10:40 - 11:35
======================================================================================
Klaus Ziegler
Institut für Physik, Universität Augsburg, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Anderson localization near spectral degeneracies:
beyond the nonlinear sigma model
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Photonic transport is studied for systems with a degenerate band structure in the presence of strong random scattering [1]. Averaging with respect to the latter leads to a graphical representation of the transition probability in a disordered photonic lattice with entangled random walks and vertices which connect three different types of propagators [2]. The corresponding convergent expansion in terms of the inverse scattering rate indicates that photons can escape from conventional Anderson localization by forming uni-directionally propagating modes. This phenomenon is reminiscent of Haldane's uni-directional edge modes in gapped photonic crystals. In contrast to the latter, though, it does not require a gap but only sufficiently strong scattering and can be described by a Fokker-Planck equation. General conditions for the creation of these modes and some applications for photonic systems are discussed.
[1] K. Ziegler, J. Phys. A: Math. Theor. 45, 033501 (2012)
[2] K. Ziegler, J. Phys. A: Math. Theor. 48, 055102 (2015)
======================================================================================
======================================================================================
Thu 11:05 - 11:35
======================================================================================
Jeremie Richard
Laboratoire Charles Fabry UMR 8501, Institut d'Optique, CNRS, Univ Paris Sud, France
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Ultracold Atoms in Disorder. Momentum Space Investigations.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Ultracold atomic systems in presence of disorder have attracted a lot of interest over the past decade, in particular to study the physics of Anderson localization (AL) in a renewed perspective. AL has been demonstrated in landmark experiments, in 1D [1,2] and 3D [3,4,5,6] configurations. However many challenges remain and new ideas have emerged, as for instance the search for original signatures of Anderson localization in momentum space [7].
Here I will present our progresses along that line where a weak localization effect has been directly observed, i.e. the Coherent Backscattering (CBS) of ultracold atoms [8]. In particular I will report on the recent observation of suppression and revival of CBS when a controlled dephasing kick is applied to the system [9]. This observation demonstrates a novel and general method, introduced by T. Micklitz and coworkers [10], to study probe phase coherence in disordered systems by manipulating time reversal symmetry of the experimental time sequence.
Finally, I will present our newest results concerning the measurement of the elastic scattering time also done in momentum space. This energy and disorder strength resolved measurement has been realized in a red and blue detuned anisotropic speckle disorder configuration. This study of an elementary parameter of diffusion in disorder allows quantitative comparison with some diffusion models, such as Born approximation and classical diffusion regimes [11].
[1] J. Billy et al., Nature 453, 891 (2008).
[2] G. Roati et al., Nature 453, 895 (2008).
[3] S. Kondov et al., Science 334, 66 (2011).
[4] F. Jendrzejewki et al., Nat. Phys. 8, 398 (2012).
[5] S. Semeghini et al., arXiv.1404.3528 (2014).
[6] C. A. Müller and B. Shapiro, Phys. Rev. Lett. 113, 099601 (2014).
[7] T. Karpiuk et al., Phys. Rev. Lett. 109, 190601 (2012).
[8] F. Jendrzejewski et al., Phys. Rev. Lett. 109, 195302 (2012).
[9] K. Müller et al., arXiv.1411.1671 (2014).
[10] T. Micklitz et al., Phys. Rev. B 91, 064203 (2015).
[11] B. Shapiro, J. Phys. A: Math. Theor. 45 (2012).
======================================================================================
======================================================================================
Thu 11:35 - 12:30
======================================================================================
Thomas Wellens
Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Scattering laser light on cold atoms:
Multiple
scattering signals from single-atom responses
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The theory of multiple scattering in dilute media that consist of a disordered collection
of discrete scatterers relies on the division of the total scattering process into single
scattering events. In standard multiple scattering theory, these are assumed to be
linear (scattered field proportional to incident field). For atomic scatterers with
transition frequency close to the laser frequency, however, nonlinear multi-photon
scattering processes are induced at high laser intensities. To account for the impact
of these processes on the multiple scattering signal, we present an approach which
combines tools of diagrammatic multiple scattering theory (ladder and crossed
diagrams) with quantum-optical methods (optical Bloch equations) [1,2]. This
approach allows us to evaluate how quantum-mechanical scattering processes
influence, both, diffusive propagation of the average light intensity through a dilute
cloud of cold atoms (with distances between the atoms much larger than the laser
wavelength), as well as effects of coherent light propagation such as coherent
backscattering.
[1] T. Wellens and B. Grémaud, Phys. Rev. Lett. 100, 033902 (2008).
[2] T. Wellens, T. Geiger, V. Shatokhin, and A. Buchleitner, Phys. Rev. A 82,
013832 (2010).
======================================================================================
======================================================================================
Thu 12:30 - 13:00
======================================================================================
Philipp Strack
Institute for Theoretical Physics, Cologne University, Germany
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Quantum statistics with fat tails of ultracold atoms coupled to an optical resonator
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
We study the far-from-equilibrium statistical mechanics of periodically driven fermionic atoms in a lossy optical resonator.
Adapting the Keldysh approach, we set up and solve a quantum kinetic Boltzmann equation in a systematic 1/N expansion with N the number of atoms. We show that the interplay of the Fermi surface with cavity losses leads to subnatural cavity linewidth narrowing, squeezed light, and a nonthermal quantum statistics of the atoms exhibiting "fat tails".
======================================================================================
======================================================================================
Thu 13:00 - 14:30 Lunch
======================================================================================
======================================================================================
Thu 14:30 - 15:25
======================================================================================
Patrick Sebbah
Institut Langevin, ESPCI ParisTech, CNRS, Paris, France
Department of Physics, The Jack and Pearl Resnick Institute for Advanced Technology, Bar-Ilan University, Ramat-Gan, Israel
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Coalescence of Anderson-localized modes and exceptional points in 2D random media
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
In non-hermitian systems, interaction between pairs of eigenstates when a set of external parameters is varied is essentially driven by the existence of exceptional points (EP). In the vicinity of an EP, eigenvalues display a singular topology: The eigenstates become indistinguishable [1] and encircling the EP in the parameter space leads to a residual geometrical phase [2, 3]. Open random media are a particular class of non-hermitian systems. There, the modal confinement may be solely driven by the degree of scattering.
For sufficiently strong scattering, the spatial extension of the modes becomes smaller than the system size, resulting in transport inhibition and Anderson-localized states [4]. We present a theoretical and numerical investigation of exceptional points in Anderson-localized random media. Coalescence at an EP between two Anderson-localized optical modes is demonstrated in a two dimensional (2D) dielectric random system. To bring the system in the vicinity of an EP, the dielectric permittivity is varied at two different locations in the random system. Our theoretical approach describes the evolution of Anderson localized modes when permittivity distribution is modified and allows to predict the position in the parameter space of the exceptional point between two localized eigenstates. We show that the accuracy of the theoretical prediction depends on the number of localized states accounted for [5].
[1] W. D. Heiss and A. L. Sannino, “Avoided level crossing and exceptional points," J. Phys. A. Math. Gen., vol. 23, pp. 1167-1178 (1990).
[2] R. Whitney and Y. Gefen, “Berry Phase in a Non-isolated System," Phys. Rev. Lett., vol. 90, p. 190402 (2003).
[3] A. Carollo, I. Fuentes-Guridi, M. Santos, and V. Vedral, “Geometric Phase in Open Systems," Phys. Rev. Lett., vol. 90, p. 160402 (2003).
[4] T. Kato, Perturbation Theory for Linear Operators (1966).
[5] N. Bachelard, J. Arlandis, C. Garay, R. Touzani, and P. Sebbah, “Coalescence of Anderson-localized modes at exceptional points in 2D random media,” arXiv:1407.8220.
======================================================================================
======================================================================================
Thu 15:25 -16:20
======================================================================================
Sergey Skipetrov
Université Grenoble Alpes, LPMMC, F-38000 Grenoble, CNRS, LPMMC, F-38000 Grenoble, France
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Localization of light in a cold-atom gas
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
An ensemble of immobile, identical two-level atoms is the simplest physical system in
which multiple scattering of light can be studied. On the one hand, the interaction of
an isolated atom with the electromagnetic field is well understood and any nontrivial
effects may be of collective origin only. On the other hand, cold-atoms systems can
be controlled and probed with great precision, thus allowing for design of high-quality
experiments [1]. One may thus hope that ensembles of cold atoms may serve as
models of more complex photonic systems for which theoretical descriptions are
difficult to develop and in which optical experiments may allow for multiple
interpretations [2].
We have recently established that Anderson localization of light cannot be realized in
a random three-dimensional ensemble of two-level atoms [3]. Localization effects are
counteracted by resonant dipole-dipole interactions between nearby atoms. These
interactions open a new, nonradiative channel for energy transport that dominates at
high atomic densities. This qualitative picture suggests that suppression of dipoledipole
interactions may be a way towards Anderson localization of light in a cloud of
cold atoms. Because such a suppression is known to occur in a magnetic field, we
now study multiple scattering of light by atoms subject to a strong external field and
show that a transition between extended and localized states indeed takes place [4].
The work in progress concerns precise characterization of the discovered localization
transition and its classification as an Anderson transition or as a transition of a
different type. Indeed, collective atomic phenomena (Dicke sub- and superradiance)
as well as dipole-dipole interactions between atoms play important roles at the
transition point and may deprive the discovered transition of the universality known
for disorder-induced localization-delocalization transitions in simpler systems.
[1] C. Cohen-Tannoudji and D. Guéry-Odelin, Advances in Atomic Physics. An
Overview (World Scientific, Singapore, 2011)
[2] T. Sperling, W. Bührer, C.M. Aegerter and G. Maret,
Nature Photonics 7, 48, (2013)
F. Scheffold and D. Wiersma, ibid. 7, 934 (2013)
[3] S.E. Skipetrov and I.M. Sokolov, Phys. Rev. Lett. 112, 023905 (2014)
[4] S.E. Skipetrov and I.M. Sokolov, arXiv:1410.3634, to appear in Phys. Rev.
Lett. (2015)
======================================================================================