booklet of abstracts

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International Workshop on Analog Quantum Simulators for many-body dynamics AQuS 2016 Internationales Wissenschaftsforum Universität Heidelberg September 05-08, 2016 Topics Quantum simulaton, certfcaton, robustness, and complexity Quantum simulaton of contnuous and latce atomic gases Exciton-Polariton condensates and their dynamics Quantum fuids of light Universality out of equilibrium Analog gravity Informaton htps://www.kip.uni-heidelberg.de/aqus/aqus2016/ Horizon 2020 FET-Proactve Consortum AQuS – Partners: Universität Heidelberg (Coordinator), LPN-CNRS Marcoussis, FU Berlin, INO-CNR Trento, LMU München, U Cambridge & TU Wien Funded by the Horizon 2020 Framework Programme of the European Union Programme & Abstracts Scientfc Board Alberto Amo (Marcoussis) Jürgen Berges (Heidelberg) Jacqueline Bloch (Marcoussis) Iacopo Carusoto (Trento) Jens Eisert (Berlin) Thomas Gasenzer (Heidelberg) Markus Oberthaler (Heidelberg) Jörg Schmiedmayer (Wien) Ulrich Schneider (Cambridge/LMU) Coordinaton Thomas Gasenzer

Transcript of booklet of abstracts

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International Workshop on

Analog Quantum Simulatorsfor many-body dynamics

AQuS 2016

Internationales WissenschaftsforumUniversität Heidelberg

September 05-08, 2016

Topics

Quantum simulaton, certfcaton, robustness, and complexityQuantum simulaton of contnuous and latce atomic gasesExciton-Polariton condensates and their dynamicsQuantum fuids of lightUniversality out of equilibriumAnalog gravity

Informatonhtps://www.kip.uni-heidelberg.de/aqus/aqus2016/Horizon 2020 FET-Proactve Consortum AQuS – Partners: Universität Heidelberg (Coordinator), LPN-CNRS Marcoussis, FU Berlin, INO-CNR Trento, LMU München, U Cambridge & TU Wien

Funded by the Horizon 2020 Framework Programme of

the European Union

Programme

& Abstracts

Scientfc Board

Alberto Amo (Marcoussis)Jürgen Berges (Heidelberg)

Jacqueline Bloch (Marcoussis)Iacopo Carusoto (Trento)

Jens Eisert (Berlin)Thomas Gasenzer (Heidelberg)

Markus Oberthaler (Heidelberg)Jörg Schmiedmayer (Wien)

Ulrich Schneider (Cambridge/LMU)

Coordinaton

Thomas Gasenzer

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Programme

Monday, 5 September 2016

11:10 OpeningChair: Markus Oberthaler

11:30 Martin Weitz (Bonn) Bose-Einstein Condensation ofPhotons and Periodic Potentialsfor Light

12:10 Philipp Hauke (Innsbruck) Quantum Fisher information asefficient entanglement witness inmany-body systems

12:50 LunchChair: Tomaž Prosen

14:30 Fabian Essler (Oxford) Thermalization and light cones ina model with weak integrabilitybreaking

15:10 Jean-Sébastien Caux (Amsterdam) Dynamics and relaxation inintegrable quantum systems

15:50 Coffee/TeaChair: Martin Weitz

16:30 Petar Jurcevic (Innsbruck) Quantum simulations with trappedions

17:10 Evening at free disposition

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Tuesday, 6 September

Chair: Alberto Amo09:00 Andrew Daley (Strathclyde) Dissipative dynamics and quantum

state engineering with ultracoldatoms

09:40 Leticia Cugliandolo (Paris) Thermal quenches in thestochastic Gross-Pitaevskiiequation: morphology of thevortex network

10:20 Coffee/TeaChair: Leticia Cugliandolo

11:10 Cristiano Ciuti (Paris) Quantum critical phenomena inopen lattice systems

11:50 Michiel Wouters (Antwerpen) Correlations in nonequilibriumpolariton quantum fluids

12:30 LunchChair: Fabian Essler

14:30 Tomaž Prosen (Ljubljana) Exactly solvable open many-bodysystems

15:10 Tomoki Ozawa (Trento) Synthetic dimensions in ultracoldatoms and photonics

15:50 Coffee/TeaChair: Michiel Wouters

16:30 Alberto Amo (Marcoussis) Out of equilibrium condensation inpolariton lattices

18:00 Dinner buffet and Posters

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Wednesday, 7 September

Chair: Andrew Daley09:00 Silvain Nascimbène (Paris) Ultracold Dysprosium gases: a

complex system from radiativetrapping to many-body physics

09:40 Jens Eisert (Berlin) Out of equilibrium dynamics ofergodic and disordered systemsand the quest for quantumsupremacy for quantum simulators

10:20 Coffee/TeaChair: Jens Eisert

11:10 Austen Lamacraft (Cambridge) Weak Many Body Localization inthe Quantum Random EnergyModel

11:50 Henrik Lüschen (Cambridge) Experimental Results onMany-Body Localization

12:30 LunchChair: Silvain Nascimbène

14:30 Nir Navon (Cambridge) From collectives excitations toturbulence in a uniform Bose gas

15:10 Markus Karl (Heidelberg) From Quenches to CriticalDynamics and Non-Thermal FixedPoints in Ultracold Bose Gases

15:50 Coffee/TeaChair: Ulrich Schneider

16:30 Thomas Schweigler (Wien) Investigating ultracold atomsystems with higher ordercorrelation functions in and out ofequilibrium

17:10 Adrien Signoles (Heidelberg) Non-equilibrium dynamics oflong-range interacting Rydbergsystems

17:50 Evening at free disposition

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Thursday, 8 September

Chair: Jörg Schmiedmayer09:00 Eugene Demler (Harvard) Bose and Fermi polarons in

ultracold atoms09:40 Tobias Osborne (Hannover) Simulating quantum fields10:20 Coffee/Tea

Chair: Eugene Demler11:10 Iacopo Carusotto (Trento) Analog Hawking physics in atomic

and optical systems12:30 Closing and Departure

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Practical Information

The local participants will wear a green sticker on their name tag. They will answerany practical questions you may have.

Location

The conference hall is in the Internationales Wissenschaftsforum Heidelberg (IWH),situated in the old town of Heidelberg at the foot of the castle hill. The address is thefollowing:

Internationales Wissenschaftsforum HeidelbergHauptstrasse 242D-69117 Heidelberg

The public transport station that is closest is “S-Bahnhof Altstadt”. It can be reachedwith the S-Bahn (lines S1 and S2) or the bus (line 33). Then it’s a 3 minutes walk indirection of the city centre to reach the IWH.The nearest parking opportunities are "Parkhaus 13" at the "Karlsplatz" (17.50 € perday) and "Parkhaus 12" at the "Kornmarkt" (13.50 € per day). It is a 3-minute walkfrom there to the IWH.For more information, please look up the local public transportation and German railwayInternet pages:http://www.vrn.de http://www.bahn.comTransportation to and from Frankfurt airport can be found at:http://frankfurt-airport-shuttles.de/en/home-2/ https://www.tls-heidelberg.de/en/There is also map with many useful annotations at:http://g.co/maps/jt46sA small map can be found at the end of this booklet.

Internet

There is a wifi Internet access in the conference hall. Connect to WLAN ’UNI-WEBACCESS’ and open your browser. It will automatically redirect to the login page.login and password: see note on whiteboard in the lecture roomThe web-page of the conference is: https://www.kip.uni-heidelberg.de/aqus/aqus2016/

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TalksBose-Einstein Condensation of Photons and Periodic

Potentials for Light

Martin Weitz

Institut für Angewandte Physik, Universität Bonn, D-53115 Bonn

Bose-Einstein condensation has been observed with cold atomic gases, quasiparticlesin solid state systems as polaritons, and more recently also with photons in a dye-filledoptical microcavity. I will here describe measurements of our Bonn group determiningthe coherence of a photon Bose-Einstein condensate and realizing periodic potentialsfor the optical quantum gas. The optical condensate is generated in a wavelength-sizedoptical cavity, where the small mirror spacing imprints a low-frequency cutoff with aspectrum of photon energies restricted to well above the thermal energy. The cavitymirrors provide a trapping potential and a non-vanishing effective photon mass, makingthe system formally equivalent to a two-dimensional gas of trapped massive bosons.Thermalization of the photon gas is reached in a number conserving way by repeatedabsorption re-emission cycles in the dye molecules. Recent experiments realizing pe-riodic lattice potentials for the photon gas will be reported, as well as measurementsinvestigating the competition of tunneling and effective photon interactions in double-well potentials.

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Quantum Fisher information as efficiententanglement witness in many-body systems

Philipp Hauke

Institute for Theoretical Physics, University of Innsbruck, Austria

Entanglement is considered a resource for quantum simulation, but it is difficult toquantify experimentally in a many-body setting. Here, we discuss scenarios wheremany-body entanglement becomes accessible via the quantum Fisher information, aknown witness for genuinely multipartite entanglement. First, we introduce a directrelation of the QFI in thermal states with linear response functions, which makes theQFI measurable with standard methods. Using this relationship, we show that close tocontinuous quantum phase transitions the QFI, and thus multipartite entanglement, isstrongly divergent. Second, we demonstrate that the quantum Fisher information canwitness many-body localized phases, showing a characteristic growth of entanglementat long times after a quantum quench. These results illustrate that the quantum Fisherinformation represents a useful and efficiently measurable witness for entanglement inquantum many-body settings.

Thermalization and light cones in a model with weakintegrability breaking

Fabian Essler

The Rudolf Peierls Centre for Theoretical Physics, University of Oxford, UnitedKingdom

I discuss the application of equation of motion techniques to study the non-equilibriumdynamics in a class of lattice models of weakly interacting spinless fermions. Ourmodel provides a simple setting for analyzing the effects of weak integrability breakingperturbations on the time evolution after a quantum quench.

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Dynamics and relaxation in integrable quantumsystems

Jean-Sébastien Caux

Institute of Physics, University of Amsterdam, The Netherlands

This talk will outline integrability-based results on the out-of-equilibrium dynamics oflow-dimensional systems such as interacting atomic gases and quantum spin chains. Anumber of recent developments will be explained, including a new method for explicitlycalculating the relaxation of observables after a quantum quench. Exact solutionsto the interaction turn-on quench in the Lieb-Liniger model and to the Néel-to-XXZquench in spin chains will be presented. Particular emphasis will be given to interestingopen issues, including the failure of the (local) Generalized Gibbs Ensemble to properlydescribe post-quench steady-state properties and the necessity to include quasilocalconserved charges to obtain correct answers.

Quantum simulations with trapped ions

Petar Jurcevic

Institut für Experimentalphysik, Universtität Innsbruck, Austria

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Dissipative dynamics and quantum state engineeringwith ultracold atoms

Andrew Daley

Department of Physics, University of Strathclyde, Glasgow, United Kingdom

The time-dependent microscopic control available over systems of ultracold atoms hasopened new opportunities to explore many-body dynamics, addressing fundamentalquestions both in and out of equilibrium. As always in such systems, a key experimentalchallenge is found in the need to cool systems to lower temperatures. However, thetime-dependent control available over these dynamics can provide a new tools forrealising low-entropy many-body states, and this is further enhanced by the possibilityto generate dissipative dynamics that are also well understood on a microscopic level.I will discuss recent developments in this area, illustrated with our recent theoreticalwork in two directions: (i) the generation of spin-entangled states of fermionic atoms inan optical lattice by combining Fermi statistics with dissipation induced by a reservoirgas not trapped by a lattice, and (ii) the application of bilayer lattice systems, togetherwith dynamical control of atoms in optical lattices, to dynamically disentangle twosubsystems and achieve sensitive many-body states via adiabatic cooling.

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Thermal quenches in the stochastic Gross-Pitaevskiiequation: morphology of the vortex network

Leticia Cugliandolo

Laboratoire de Physique Théorique et Hautes Energies, Sorbonne Universités -Université Pierre et Marie Curie

A system taken across a second order phase transition from its disordered into itssymmetry-broken phase undergoes a phase ordering process. Topological defects areleft in the system at finite times after the quench and, in open systems, they aregradually eliminated in the course of evolution towards equilibrium.I will discuss a recent detailed study of the evolution of 3d weakly interacting bosons atfinite chemical potential, taken across their phase transition, using the stochastic Gross-Pitaevskii equation. In short, I will explain the full characterisation of the vortex networkin and out of equilibrium. This is work in collaboration with Michikazu Kobayashi(Kyoto University).

Quantum critical phenomena in open lattice systems

Cristiano Ciuti

Univ. Paris Diderot, Paris, France

In this invited talk, I will present recent theoretical results of my group about non-equilibrium critical phenomena in open quantum systems. In particular, I will showpredictions for driven-dissipative photonic systems and also dissipative spin lattices.

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Correlations in nonequilibrium polariton quantumfluids

Michiel Wouters

Universiteit Antwerpen, Antwerpen (Wilrijk), Belgium

Microcavity polaritons interact much stronger than photons, but can still be safelydescribed by the Bogoliubov approximation. I will discuss the coherence propertiesof both resonant and nonresonantly excited polariton condensates. For the case ofpulsed resonant excitation, connections to the dynamical Casimir effect and quenchesin many-body systems can be made.

Exactly solvable open many-body systems

Tomaž Prosen

Faculty of Mathematics and Physics, University of Ljubljana, Slovenia

I will discuss several examples of one-dimensional interacting open quantum many-bodysystems for which one can write exact solution for the steady state, or even computethe full Liouvillian spectrum of decay modes. Among the most prominent ones are theboundary driven XXZ and fermi Hubbard chains, the former displaying a non-equilibriumquantum phase transition in the steady state, while the full spectrum of the XX chainwith de-phasing bulk noise and possible boundary driving can be shown to be equivalentto Bethe-ansatz spectrum of the Hubbard model with imaginary interaction U.

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Synthetic dimensions in ultracold atoms andphotonics

Tomoki Ozawa

Dipartimento di Fisica, INO-CNR BEC Center and University of Trento, Povo (TN),Italy

I discuss recent developments of the study of “synthetic dimensions” in ultracold gasesand photonics. The idea of synthetic dimensions is to identify internal states of anatom or a photonic cavity as extra dimensions, and to simulate higher dimensionallattice models using physically lower dimensional systems. The concept was originallyproposed and experimentally realized in ultracold gases. I first review the existingtheoretical and experimental studies of synthetic dimensions. After discussing somechallenges and limitations of the existing methods of synthetic dimensions, I explainour proposals of realizing synthetic dimensions both in ultracold gases and in photoniccavities, which overcome some of these limitations. Finally I discuss how the fourdimensional quantum Hall effect can be observed in ultracold gases and photonicsusing the synthetic dimensions.

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Out of equilibrium condensation in polariton lattices

F. Baboux1, D. De Bernardis2, C. Gomez1, E. Galopin1, A. Lemaître1, L.Le Gratiet1, I. Sagnes1, A. Amo1, M. Wouters1, J. Bloch1,3

1Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, UniversitéParis-Saclay, C2N Marcoussis, 91460 Marcoussis, France

2Theory of Quantum and Complex Systems, Universiteit Antwerpen, Universiteitsplein1, B-2610 Antwerpen, Belgium

3Physics Department, École Polytechnique, F-91128 Palaiseau Cedex, France

Exciton polaritons in semiconductor microcavities provide an excellent platform tostudy the out-of-equilibrium properties of interacting quantum fluids. An importantcharacteristic of polariton condensates is that they coexist with a bath of reservoirparticles at high energies in a far-from-thermal state [1]. The combination of bosonicstimulation with the interactions between condensed and non-condensed polaritonsresults in an effective attractive interaction [2]. This gives rise to strong instabilitiesthat destroy the polariton condensate when using large excitation spots []. Here wewill show evidence of this instability and how polariton condensates can become stablein a periodic lattice. The stabilisation of polariton condensates demonstrated in thiswork, opens a new paradigm in polariton physics, allowing the exploration of theKardar–Parisi–Zhang physics, and provide a route for the spatial engineering of thesign of the interactions.

[1] F. Baboux et al., Bosonic Condensation and Disorder-Induced Localization in a FlatBand. Phys. Rev. Lett. 116, 066402(2016).

[2] N. Bobrovska, E. A. Ostrovskaya, and M. Matuszewski, Stability and spatial co-herence of nonresonantly pumped exciton-polariton condensates. Phys. Rev. B 90,205304 (2014).

[3] K. S. Daskalakis, S. A. Maier, and S. Kéna-Cohen, Spatial Coherence and Stabilityin a Disordered Organic Polariton Condensate. Phys. Rev. Lett. 115, 035301 (2015).

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Ultracold Dysprosium gases: a complex system fromradiative trapping to many-body physics

Sylvain Nascimbène

LKB ENS Paris, Laboratoire Kastler Brossel, Collège de France, Paris, France

Atomic Dysprosium features a complex electronic structure, which leads to several in-teresting properties in the context of atomic physics: a large electronic angular momen-tum, a large magnetic moment, many narrow optical transitions. Those characteristicsimply specific physical behaviors, from the radiative cooling and trapping to the designof novel schemes for quantum many-body physics.We will first present a detailed study of the magneto-optical trapping (MOT) of ul-tracold Dysprosium. We will show that the MOT can be operated in several regimes,with either all or a single Zeeman components involved. Due to the weak radiativeforces obtained with a narrow optical transition, gravity plays an major role, and tendsto polarize the atomic sample. We will also discuss light-induced inelastic collisions.The second part of the talk will address the prospects of our experiment, which aimsat realizing topological superfluids with ultracold Dysprosium. We will show that thestructure of optical transitions is well suited for realizing light-induced gauge fields,the basic ingredient for realizing a topological superfluid. We will also present severalschemes to reveal the presence of Majorana fermions at the edges of the topologicalsuperfluid.

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Out of equilibrium dynamics of ergodic anddisordered systems and the quest for quantum

supremacy for quantum simulators

Jens Eisert

Dahlem Center for Complex Quantum Systems, Freie Universität Berlin,Berlin-Dahlem, Germany

Dynamical analogue quantum simulators allow to probe a plethora of physical phenom-ena related to the physics of quantum systems out of equilibrium. In this talk, wewill consider questions of equilibration, Gaussification, the dynamics of quantum phasetransitions and the absence of thermalisation - present in disordered interacting modelsthat show features of the multi-faceted phenomenon of many-body localisation. Wediscuss both new theoretical results, as well as tools employed in collaborations withexperimentalists working with cold atoms in optical lattices and on atom chips.In the last part of the talk, we will have a look at work in progress on conceptualquestions that seem to be key to the idea of a quantum simulator: This in on the onehand one of how to devise quantum simulators that have the potential of computation-ally outperforming classical devices, discussing variants of IQP circuits. On the otherhand, it the question of the certification of quantum simulators for which no classicalsimulation algorithm is known.

Weak Many Body Localization in the QuantumRandom Energy Model

Austen Lamacraft

Cavendish Laboratories, University of Cambridge, United Kingdom

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Experimental Results on Many-Body Localization

Henrik Lüschen

Fakultät für Physik, Max Planck Institute of Quantum Optics, München, Germany

The phenomenon of many-body localization (MBL) describes a generic non-thermalizing phase in which quantum information can persist locally up to infinitetimes. MBL is separated from a phase obeying the eigenstate-thermalization hypoth-esis via a disorder driven dynamical phase transition, which happens not only in theground state but over an extended range of energy densities. An effect similar to finitetemperatures smearing out ground state phase transitions into universal crossovers isexpected in the presence of a small coupling to an external heat bath.I will present recent experimental results on the MBL phase transition, as well as MBLin the presence of a weak photon bath, based on the relaxation of fast local observablesin a quasi-random optical lattice. We find slow powerlaw dynamics close to the MBLcritical point, which is potentially connected to Griffith type effects. Also, in thepresence of controllable weak photon scattering, we observe restoration of ergodicityon a timescale dependent on the microscopic parameters of the Hamiltonian.

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From collectives excitations to turbulence in auniform Bose gas.

Nir Navon

University of Cambridge, United Kingdom

The recent realisation of Bose-Einstein condensates in uniform traps has opened inter-esting possibilities to study far-from-equilibrium phenomena with textbook systems. Inthis talk, we will present a study where we drive a homogeneous Bose-Einstein con-densate (BEC) out of equilibrium with an oscillating force that pumps energy into thesystem at the largest lengthscale. In the limit of weak drives, the BEC’s response islinear, well captured by its lowest-lying excitations. For stronger drives, a nonlinearresponse is apparent and we observe a gradual development of a cascade characterisedby an isotropic power-law distribution in momentum space. We will report on our latestprogress on the detailed characterisation of the steady-state turbulent state, as well asa joint experimental/theoretical investigation into the finite-temperature behaviour ofthe BEC lowest-lying mode.

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From Quenches to Critical Dynamics andNon-Thermal Fixed Points in Ultracold Bose Gases

Markus Karl

Kirchhoff Institut für Physik, Universität Heidelberg, Deutschland

Ultracold quantum gases provide a vast playground for exploring dynamical critical phe-nomena, such as phase transitions and universal scaling far from equilibrium. Here, weconsider one- and multi-component (spin) systems of ultracold Bose gases, inducinghighly non-linear dynamical evolution via sudden parameter quenches and instabili-ties. We identify critical scaling and universal scaling forms in the post-quench timeevolution of the respective systems. For quenches within the symmetric phase of atwo-component Bose gas, we show that shorttime quench dynamics can be describedby a universal crossover function, where the quench-induced energy appears as the rel-evant energy scale. Scaling properties have been found which indicate the importanceof pre-thermalisation temperatures long before dephasing has occurred in the nearlygapless system. We discuss the theoretical results in the light of and illustrated byrecent experimental measurements. For the single-component gas, we find a new uni-versal phase of time evolution, characterised by an anomalously slow, glass-like, phaseordering process of vortex defects in the symmetry-broken phase. We discuss our re-sults, in particular, for dynamical universal scaling forms in the light of the concept ofnon-thermal fixed points.

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Investigating ultracold atom systems with higherorder correlation functions in and out of equilibrium

Thomas Schweigler

Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Austria

We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids,which realize the quantum sine-Gordon model relevant for a wide variety of disciplinesfrom particle to condensed-matter physics. From measured interference patterns weextract phase correlation functions and analyze if, and under which conditions, thehigher-order correlation functions factorize into lower ones. This allows us to charac-terize some essential features of the model solely from our experimental measurements.The method is also used to investigate the non-equilibrium dynamics following a quenchin the tunnel-coupling strength between the superfluids.

Non-equilibrium dynamics of long-range interactingRydberg systems

Adrien Signoles

Physical Institute, Heidelberg University, Germany

Rydberg atoms in ultracold gases constitute controllable systems to experimentallystudy non-equilibrium phenomena. Of specific interest is the possibility to introduceresonant dipolar exchange interactions. This provides new opportunities for investi-gating the dynamics of strongly correlated many-body quantum systems with beyond-nearest neighbour coupling.Here we present an experimental realization of such a system, by exciting nS and nPRydberg states and coupling them with microwave fields, which allow for studying dy-namics of correlated spin systems. We report the observation of interaction-inducedeffects in the dynamics of this ensemble of atoms and show that the system can beunderstood in terms of a dipolar XX model, providing a benchmark for spin systems. Iwill review recent theoretical and experimental progress in the study of Bose and Fermipolarons in ultracold atoms. The emphasis will be on understanding non-equilbriumaspects such as dynamics of polaron formation probed by Ramsey interferometry

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Bose and Fermi polarons in ultracold atoms

Eugene Demler

Harvard University, Cambridge, MA 02138, USA

I will review recent theoretical and experimental progress in the study of Bose and Fermipolarons in ultracold atoms. The emphasis will be on understanding non-equilbriumaspects such as dynamics of polaron formation probed by Ramsey interferometry

Simulating quantum fields

Tobias Osborne

Institut für Theoretische Physik, Leibniz Universität Hannover, Germany

During the past decades we have seen important hints coming from string theory andholography – particularly in the study of 4D SUSY gauge theories – that the parametri-sation of QFTs in terms of lagrangians via the path integral is not always the mostefficient representation. Thus, given the success of tensor networks in condensed mat-ter theory, it seems worthwhile to contemplate how to formulate QFT directly in termsof a state represented as a TNS. Doing this directly suggests new quantum simulationalgorithms for interacting quantum fields. In this talk I will describe the modern Wilso-nian approach to defining QFT and explain how to implement this approach directly interms of TNS and describe how to take the continuum limit of tensor networks rangingfrom matrix product states, projected entangled pair states, tree tensor networks, andthe multiscale entanglement renormalisation ansatz. These continuum limits then formthe basis for quantum simulation algorithms, both analog and discrete, which allow fora direct comparison between the simulation results coming from discretisations and thedesired continuum theory.

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Analog Hawking physics in atomic and opticalsystems

Iacopo Carusotto

BEC Trento, INO-CNR BEC Center, 38123 Povo (Trento), Italy

In this talk I will present the latest advances of the AQuS project in the study of analogmodels of black holes using condensed matter and optical systems.In the first part of the talk, I will focus on the stimulated and spontaneous Hawkingemission of phonons in a flowing fluid of polaritons in a semiconductor microcavityand I will outline the perspectives in view of an experimental observation. I will thenreview on-going theoretical studies of the consequences of the non-equilibrium conditionon the quantum properties of the Hawking emission polariton fluids, and of Hawkingemission in atomic gases with spin degrees of freedom or trapped in a elongated two-well potential. I will conclude with an outline of more speculative investigations inthe direction of highlighting the back-reaction effect of Hawking emission onto thecondensate motion.

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PostersExploring few-fermion systems in single- and

multi-well potentials

A. Bergschneider , V. M. Klinkhamer, J. H. W. Becher,M. Dehabe, G. Zürn, P. M. Preiss and S. Jochim

Physikalisches Institut der Universität Heidelberg, 69120 Heidelberg, Germany

We present several measurements that use ultracold fermionic atoms to investigate thecrossover from few to many-body physics in different kinds of quantum systems. Themeasurements follow a bottom-up approach: We first generate and control the smallestrealization that contains the relevant physics and then gradually increase the size ofthe system.With our setup, we can generate one or several cigar-shaped potentials to trap ultracoldatoms. We deterministically prepare few fermions in these potential wells with fullcontrol over the particle number and the quantum state of the system. Furthermore,we can tune the interparticle interactions between the fermions over a large range.In a first set of experiments we studied the transition from few- to many-body physicsin a one-dimensional system. We prepared a single impurity and an increasing numberof majority particles in a single well and studied the interaction energy as a function ofthe number of majority atoms [1]. We also realized few-particle antiferromagnetic spinchains by starting with noninteracting two-component systems in one well and rampingto strong repulsion [2].Recently, we prepared two fermions in the ground state of a double-well potential anddemonstrated full control and tunability of this system without increasing its entropy.This system can be considered as the fundamental building block of the Fermi-Hubbardmodel. Combining several double wells can allow to prepare low-entropy states in afew-site lattice [3].

[1] A. N. Wenz et al., Science 342, 457(2013).[2] S. Murmann et al., in preparation.[3] S. Murmann et al., PRL 114, 080402 (2015).

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Black-Hole lasing in spinorial condensates

Salvatore Butera

Heriot-Watt University, Edinburgh, United Kingdom

We study the analogue of the Hawking radiation physics in a coherently coupled twocomponent Bose-Einstein condensate. In practice, we consider a gas of two level atoms,whose internal states are coupled by an external laser field. Both for the homogeneousand the harmonically trapped (quasi-) one-dimensional system we show, by properlytuning the mean-field coupling constants and the Rabi frequency of the light-atomsinteraction, the occurrence of the black-hole lasing effect respectively in the densityand in the spin-density branches of the fluctuation field.The advantage of considering this set-up relies on the high controllability of the pa-rameters of the light-atoms interaction in state-of-the-art cold-atom experiments andon the fact that, coupling the internal states by a two-photons Raman interaction,the inhomogeneity of the laser-atom interaction do not locally modify the chemicalpotential of the system, which remain homogeneous over all the condensate withoutthe necessity of opportunely tailoring the external confining potential.

Topological Varma superfluid in optical lattices

Marco Fedele Di Liberto

INO-CNR BEC Center Trento, 38123 Povo (Trento), Italy

Topological states of matter are peculiar quantum phases showing different edge andbulk transport properties connected by the bulk-boundary correspondence. While non-interacting fermionic topological insulators are well established by now and have beenclassified according to a ten-fold scheme, the possible realisation of topological states forbosons has not been much explored yet. Furthermore, the role of interactions is far frombeing understood. Here, we show that a topological state of matter exclusively drivenby interactions may occur in the p-band of a Lieb optical lattice filled with ultracoldbosons. The single-particle spectrum of the system displays a remarkable parabolicband-touching point, with both bands exhibiting non-negative curvature. Although thesystem is neither topological at the single-particle level, nor for the interacting groundstate, on-site interactions induce an anomalous Hall effect for the excitations, carryinga non-zero Chern number. Our work introduces an experimentally realistic strategy forthe formation of interaction-driven topological states of bosons.

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Far from equilibrium integrable systems

Sebastian Erne

Institute for theoretical Physics, Heidelberg University, Germany

Relaxation of far-from equilibrium integrable systems is to date an open and interestingquestion. Recent progress in cold atom experiments in low dimensional systems, allowfor a detailed study of integrable field theories. Specifically we consider a system oflinearly coupled quasi one-dimensional condensates, realizing the quantum sine-Gordonand Lieb-Liniger theories. By studying quenches in the sine-Gordon model, we areable to explore fundamental questions of quantum physics. In particular we investi-gate prethermalization and the Generalized Gibbs Ensemble, higher order correlationsand their factorization properties in and out of equilibrium, dynamics and decay oftopological excitations and false vacua, quantum many body revivals, and tomogra-phy of quasiparticle. We compare the experiment to analytical and numerical results,for the latter using the (stochastic) Gross-Pitaevskii equations as well as Monte-Carlosimulations.

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Verify Many-Body Entanglement via StructureFactor Measurements

Oliver Marty

Institut für Theoretische Physik, Universität Ulm, Germany

A fascinating example of a genuine quantum effect is the concept of spin-squeezing thatdescribes a collective property of an aggregation of spins. Since its first considerationin the context of quantum metrology a central application of spin-squeezing parametersbecame the detection of multipartite quantum correlations, that is, quantitatively thedegree of spin-squeezing is a measure of multipartite entanglement. Entanglementcriteria based on spin-squeezing parameters benefit from the fact that these parametersusually depend on simple and global observables only, in particular, typically on low-order moments of collective spin operators. As a consequence, the approach providesan experimentally easily accessible and robust way for entanglement detection that isfree of any assumptions on the system and may therefore be suitable for many differentplatforms. Motivated by a criteria of Sorensen and Molmer [PRL 86, 4431 (2001)]for multipartite entanglement, our contribution is a general scheme, that allows forthe detection of many-body entanglement via a variety of observables. As an examplewe present entanglement criteria based on the structure factor, an observable whichcan be measured in neutron scattering experiments, but may also be accessible onother platforms such as trapped ions. To explicitly obtain the criteria we combine arecently introduced algorithm for eigenvalue optimization [Mengi, 35, 2 (2014)] withmatrix-product states and operator based techniques that theoretically allows for thedetection of multipartite entanglement of hundreds of spins. To support the practicalimportance of our scheme, we discuss states which are optimally detected and showhow they can be created in experiments with trapped ions. Generally, our approachprovides a scalable method to verify multipartite entanglement which may find a varietyof applications, e.g., as a benchmark of various experimental situations, ranging fromquantum simulators to adiabatic quantum optimization.

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Exact Bethe ansatz spectrum of a tight-bindingchain with dephasing noise

Mariya Medvedyeva

Faculty of Mathematics and Physics, University of Ljubljana, Slovenia

We construct an exact map between a tight-binding model on any bipartite lattice inpresence of dephasing noise and a Hubbard model with imaginary interaction strength.In one dimension, the exact many-body Liouvillian spectrum can be obtained by ap-plication of the Bethe ansatz method. We find that both the non-equilibrium steadystate and the leading decay modes describing the relaxation at late times are related tothe eta-pairing symmetry of the Hubbard model. We show that there is a remarkablerelation between the time-evolution of an arbitrary k-point correlation function in thedissipative system and k-particle states of the corresponding Hubbard model.

Probing the Dynamics of Superradiant QuantumPhase Transition in a Single Trapped-Ion

Ricardo Puebla

Institute of Theoretical Physics, Ulm University, Germany

The Rabi model can undergo a superradiant quantum phase transition (QPT) despiteconsisting of a single two-level system and a single bosonic mode [1]. Here wedemonstrate that the QPT and its critical dynamics near the QPT can be probedin the setup of a single trapped ion, making use of equilibrium and non-equilibriumuniversal functions of the Rabi model. We propose a scheme that can faithfully realizethe Rabi model in the extreme parameter regime to observe critical behavior: largeratio of the effective atomic transition frequency to the oscillator frequency. It isdemonstrated that the predicted universal functions can indeed be observed basedon our scheme. Finally, the effects of realistic noise sources on probing the universalfunctions in experiments are examined [2].

[1] M.-J. Hwang, R. Puebla, and M. B. Plenio, Phys. Ref. Lett. 115, 180404(2015).[2] R. Puebla, M.-J. Hwang, J. Casanova, and M. B. Plenio, arxiv:1607.03781.

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Topological Mechanics

Grazia Salerno

INO-CNR BEC Center, 38123 Povo (TN) Italy

We theoretically propose how to observe topological effects in a generic classical systemof coupled harmonic oscillators, whose oscillation frequency is modulated fast in time.Making use of Floquet theory in the high-frequency limit, we identify a regime in whichthe system is accurately described by a Harper-Hofstadter model where the syntheticmagnetic field can be externally tuned via the phase of the frequency modulation of thedifferent oscillators. We illustrate how the topologically protected chiral edge states, aswell as the Hofstadter butterfly of bulk bands, can be observed in the driven-dissipativesteady state under a monochromatic drive. In analogy with the integer quantum Halleffect, we show how the topological Chern numbers of the bands can be extractedfrom the mean transverse shift of the steady-state oscillation amplitude distribution.Finally, we discuss the regime where the analogy with the Harper-Hofstadter modelbreaks down.

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Probing Relaxation at the Many-Body Localization(MBL) Transition with Ultracold Fermions in Optical

Lattices

Sebastian Scherg

Quantum Optics Chair, Ludwig-Maximilians Universität München, Germany

The many-body localization transition is a dynamical phase transistion, which happensover an extended range of energy densities.The phase transistion seperates an ergodic, thermal phase, in which the eigenstate ther-malization hypothesis (ETH) holds, from a non-thermal, localized phase, which violatesthe ETH. We study this transistion using interacting Fermions in a one-dimensionalquasi-disordered optical lattice by monitoring the decay of an initially imprinted localdensity pattern.I will show recent experimental results on MBL focusing on the vicinity of the MBL criti-cal point, where we find slow powerlaw dynamics, which might potentially be connectedto Griffith type effects. Furthermore, I will present recent experiments on periodicaldriving of an MBL system, resulting in a localized phase at high drive frequencies andan ergodic phase at low ones. Finally, I will explain recent preliminary data about MBLin a 2D environment.

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Nonthermal Fixed Points and Superfluid Turbulencein Ultracold Bose Gases

Markus Karl, Christian-Marcel Schmied, Stefanie Czischek

Kirchhoff-Institute for Physics, Heidelberg University, Germany

Ultracold quantum gases provide various means to probe universal many-body dynamicsfar from equilibrium. Here, we focus on the non-linear dynamical evolution inducedin an ultra cold Bose gas by a sudden initial parameter quench. Considering one-or multi-component (spin) systems, various types of spatial and wavenumber- spacepatterns emerge, being characterized by universal scaling functions associated withnon-thermal fixed points. Such fixed points can be observed in existing experimentsand are closely related to quantum turbulence usually discussed in systems of morethan one spatial dimension. While these situations are associated with quenches toa symmetry-broken state, quenches within the symmetric phase offer a way to probethe properties of universal dynamics similar to those near a quantum critical point inequilibrium. Scaling properties have been found which indicate the importance of pre-thermalisation temperatures long before dephasing has occurred in the nearly gaplesssystem. We discuss the theoretical results in the light of and illustrated by recentexperimental measurements.

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Heteronuclear Efimov scenario in an ultracoldBose-Fermi mixture with large mass imbalance

Juris Ulmanis

Physics Institute, Heidelberg University, Germany

Universality in few-body systems is a prominent topic in fundamental quantum physics.One of its hallmarks is the Efimov effect, where pairwise resonantly interacting particlescan form an infinite geometric series of weakly-bound three-body states, the Efimovstates, following a discrete scaling law. Due to the large mass imbalance, an ultracoldBose-Fermi mixture of Cs and Li atoms features a drastically reduced scaling factor,making it a prototypical system for the thorough investigation of the heteronuclearEfimov effect. Here we present our recent measurements and analysis of three-bodyrecombination spectra of Li+Cs+Cs collisions close to two broad Li-Cs Feshbach res-onances. We observe how the heteronuclear Efimov scenario is critically modified bythe sign of the Cs-Cs intraspecies interaction and compare our results with universalzero-range and van der Waals theories. Our findings show that the three-body param-eter and the scaling factor between consecutive resonances are controlled not only bythe van der Waals forces, but also by the scattering length between the two bosons,independent of short-range physics.

New Geometries for Ultracold Atoms in OpticalLattices

Konrad Viebahn

Cavendish Laboratory, University of Cambridge, United Kingdom

We will present the latest developments on our new apparatus involving ultracold potas-sium and rubidium atoms in novel optical lattice geometries.

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Role of geometry in nonlocal superfluids

Kali Wilson

Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh,United Kingdom

In this work we perform numerical and experimental studies that demonstrate the keyrole of fluid geometry when the fluid is also nonlocal. We show that the Bogoliubovdispersion relation associated with elementary excitations in a nonlocal quantum fluidmay be modified by the system geometry, such that the system can be pushed intoa regime where superfluid behavior is observed despite a high degree of nonlocality.This interplay between geometry and nonlocality is a general feature of the nonlocalinteraction, with applications to dipolar BECs and nonlocal photon fluids. Tailoringthe system geometry thus provides external control of the effective nonlocal lengthcharacterizing the fluid, and sets a threshold wavevector below which a linear, sonicdispersion relation consistent with superfluidity may be observed. We discuss this in-terplay in the context of recent experimental observations of superfluid behavior in aroom-temperature, nonlocal photon fluid in a propagating geometry. We have exper-imentally observed signatures of superfluid behavior in the dispersion relation, and inthe nucleation of vortex cores as the photon fluid flows past an extended obstacle,despite working with a highly-nonlocal thermal nonlinearity expected to suppress suchsuperfluid behavior.

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Participants

• L. Angenoorth (Universität Heidelberg,Germany)

• A. Amo (Centre for Nanosciences andNanotechnologies (C2N), France)

• K. Baumann (Goethe UniversitätFrankfurt, Germany)

• A. Bergschneider (Universität Heidelberg,Germany)

• S. Butera (Heriot-Watt UniversityEdinburgh, United Kingdom)

• I. Carusotto (BEC Trento, Italy)

• J.-S. Caux (University of Amsterdam,The Netherlands)

• C. Ciuti (Univ. Paris Diderot, France)

• L. Cugliandolo (Université Pierre etMarie Curie, France)

• S. Czischek (Universität Heidelberg,Germany)

• A. Daley (University of Strathclyde,United Kingdom)

• E. Demler (Harvard University, USA)

• M. F. Di Liberto (INO-CNR BEC CenterTrento, Italy)

• J. Eisert (Freie Universität Berlin,Germany)

• T. Enss (Universität Heidelberg,Germany)

• S. Erne (Heidelberg University,Germany)

• F. Essler (University of Oxford, UnitedKingdom)

• T. Gasenzer (Universität Heidelberg,Germany)

• K. Geier (Universität Heidelberg,Germany)

• P. Hauke (University of Innsbruck,Austria)

• M. Holten (Universität Heidelberg,Germany)

• F. Jendrzejewski (Universität Heidelberg,Germany)

• P. Jurcevic (University of Innsbruck,Austria)

• M. Karl (Universität Heidelberg,Germany)

• M. Kastner (Stellenbosch University,South Africa)

• P. Kunkel (Universität Heidelberg,Germany)

• A. Lamacraft (University of Cambridge,United Kingdom)

• D. Linnemann (Universität Heidelberg,Germany)

• H. Lüschen (MPQ/LMU, Germany)

• O. Marty (Universität Ulm, Germany)

• M. Medvedyeva (University of Ljubljana,Slovenia)

• S. Nascimbène (LKB ENS Paris, France)

• N. Navon (University of Cambridge,United Kingdom)

• M. Oberthaler (Universität Heidelberg,Germany)

• T. Osborne (Leibniz UniversitätHannover, Germany)

• T. Ozawa (INO-CNR BEC Center andUniversity of Trento, Italy)

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• T. Prosen (University of Ljubljana,Slovenia)

• M. Prüfer (Universität Heidelberg,Germany)

• R. Puebla (Ulm University, Germany)

• M. Rabel (Universität Heidelberg,Germany)

• G. Salerno (INO-CNR BEC Center, Italy)

• A. Salzinger (Universität Heidelberg,Germany)

• S. Scherg (Ludwigs-MaximiliansUniversität München, Germany)

• C.-M. Schmied (Heidelberg University,Germany)

• J. Schmiedmayer (TU Wien, Austria)

• U. Schneider (University of Cambridge,United Kingdom / Ludwigs-MaximiliansUniversität München, Germany)

• T. Schweigler (TU Wien, Austria)

• A. Signoles (Universität Heidelberg,Germany)

• H. Strobel (Universität Heidelberg,Germany)

• A. Tarkhov (Skolkovo Institute of Scienceand Technology, Russia)

• L. Todorov (Durham University, UnitedKingdom)

• J. Ulmanis (Heidelberg University,Germany)

• K. Viebahn (University of Cambridge,United Kingdom)

• M. Weitz (Universität Bonn, Germany)

• K. Wilson (Heriot-Watt University,United Kingdom)

• M. Wouters (Universiteit Antwerpen,Belgium)

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Committees

Scientific board

• Alberto Amo (Marcoussis)• Jürgen Berges (Heidelberg)• Jacqueline Bloch (Marcoussis)• Iacopo Carusotto (Trento)• Jens Eisert (Berlin)• Thomas Gasenzer (Heidelberg)• Markus Oberthaler (Heidelberg)• Jörg Schmiedmayer (Vienna)• Ulrich Schneider (Cambridge/Munich)

Coordinator

• Thomas Gasenzer (Kirchhoff-Institut für Physik, Universität Heidel-berg)

Contact

Conference Assistant

Christiane JägerUniversität HeidelbergSynthetic Quantum Systems

Kirchhoff-Institut für PhysikIm Neuenheimer Feld 22769120 HeidelbergGermany

tel: +49 6221 54 5172fax: +49 6221 54 5179e-mail: [email protected]: http://www.kip.uni-heidelberg.de/matterwaveoptics/

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IndexProgramme 3

Practical Information 7Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Talks 9Martin Weitz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Philipp Hauke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Fabian Essler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Jean-Sébastien Caux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Petar Jurcevic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Andrew Daley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Leticia Cugliandolo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Cristiano Ciuti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Michiel Wouters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Tomaž Prosen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Tomoki Ozawa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Alberto Amo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Sylvain Nascimbène . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Jens Eisert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Austen Lamacraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Henrik Lüschen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Nir Navon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Markus Karl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Thomas Schweigler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Adrien Signoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Eugene Demler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Tobias Osborne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Iacopo Carusotto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Posters 25Andrea Bergschneider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Salvatore Butera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Marco Fedele Di Liberto . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Sebastian Erne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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Oliver Marty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Ricardo Puebla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Grazia Salerno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Sebastian Scherg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Christian-Marcel Schmied . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Juris Ulmanis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Konrad Viebahn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Kali Wilson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Participants 34

Committees 36

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Internet

There is a wifi Internet access in the conference hall. Connect to WLAN ’UNI-WEBACCESS’ and open your browser. It will automatically redirect to the loginpage.login: iq3password: 8x7du

The web-page of the conference is:

http://www.thphys.uni-heidelberg.de/ smp/RETUNE2012/index.php

It contains additional information about the conference. We will try to assemblethe material of the conference and make it available on the web-page as well.

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