
Chair: Peter Domokos

09:00  10:30

Andrew Daley
(University of Strathclyde)
Numerical methods for opensystem dynamics I

10:30  11:00

Coffee break

11:00  11:30

Cecilia Cormick
(CONICET and Universidad Nacional de Córdoba)
Ion chains in pumped optical resonators
The equilibrium configuration of a chain of trapped ions subjected to an optical potential depends, in general, on the competition between the forces resulting from the trap, the Coulomb repulsion, and the optical field. We theoretically explore new possibilities that come into play when the optical potential is provided by a laserpumped highquality resonator: photons leaking out of the cavity can be used to nondestructively monitor the system, and the optomechanical coupling of fluctuations allows one to implement cavity cooling of the chain motion, to the ground state in appropriate regimes. Furthermore, when the backaction of the particles on the field intensity is relevant, it leads to an infinitely ranged effective interaction between ions, introducing drastic changes in the critical properties of the chain across structural transitions. In particular, we study the transitions between linear and zigzag configurations, and between sliding and pinned phases, and observe the appearance of hysteresis and bistability in otherwise continuous transitions. Finally, we show that this kind of setup can also be used to study the transition between commensurate and incommensurate configurations, namely, a regime where the interparticle distance is pinned at a multiple of the potential periodicity, and another one in which particle density can vary due to the formation of defects.

11:30  12:30

Jonathan Keeling
(University of St Andrews)
Introduction to cavity QED, including new topics in manybody cavity QED I

12:30  13:30

Lunch break

13:30  14:00

Discussion


Chair: Emanuele G. Dalla Torre

14:00  15:00

Jonathan Keeling
(University of St Andrews)
Introduction to cavity QED, including new topics in manybody cavity QED II

15:00  15:30

Tobias Donner
(ETH Zurich)
Drivendissipative crystals of matter and light
The coupling of a quantum gas to the field of an optical highfinesse cavity can be employed to induce globalrange atomic interactions. If these are sufficiently strong, such a drivendissipative manybody system undergoes a structural phase transition.
Introducing a 3D optical lattice to this system, the collisional shortrange interactions can be brought to competition with these globalrange interactions and – at the same time – with the zeropoint motion of the particles. The resulting phase diagram hosts four distinct phases – a superfluid, a lattice supersolid, a Mott insulator and a charge density wave. We study the metastable dynamics when driving the system from the Mott insulator to the charge density wave phase.
In a different set of experiments, we couple a superfluid cloud of atoms simultaneously to two intersecting optical cavities. This arrangement leads to a symmetry enhancement and the resulting system exhibits a continuous spatial U(1)symmetry. The combination of two continuous symmetries – the gauge symmetry of the superfluid and the spatial symmetry – is a prerequisite for a supersolid state of matter, which we investigate in our experiments.

15:30  15:50

Coffee break

15:50  16:00

Leonie Mück
(PLOS ONE)
PLOS ONE  physical sciences division call

16:00  16:30

André Eckardt
(MPIPKS Dresden)
Nonstandard Bose Condensation in Nonequilibrium Steady States
I will speak about Bose condensation in nonequilibrium steady states of drivendissipative Bose gases, considering three basic scenarios: periodically forced (Floquet) systems coupled to a heat bath [1], systems coupled to two heat baths of different temperature [2], and pumped lossy photonic systems interacting with a heat bath [3]. Unlike equilibrium states, which are determined completely by a few thermodynamic variables like the bath temperature only, nonequilibrium steady states obey less restrictions and depend sensitively on the very details of the environment. This offers great freedom to tailor the properties of a quantum system by engineering its environment. Among others, we show that this freedom can be used for the robust preparation of excitedstate and fragmented Bose condensates. We also demonstrate that Bose condensation can be induced by coupling a system to two competing baths, both of which have temperatures well above the equilibrium critical temperature [2]. Moreover, for a broad class of models describing a variety of complex photonic systems, we predict a cascade of transitions when the pump power is ramped up [3]: First, above a threshold, the mode with the largest effective gain becomes macroscopically occupied (corresponding to simple lasing). Ramping up the pump further, further transitions can occur where single modes acquire or loose macroscopic occupation, eventually leading to a macroscopic occupation of the ground state alone (resembling equilibrium Bose condensation). Our theory describes experimental data for a twomode microcavity and excitonpolaritons in a double well [Galbiati et al. PRL 108, 126403 (2012)].
Based on references:
[1] D. Vorberg et al., PRL 111, 240405 (2013) & PRE 92, 062119 (2015)
[2] A. Schnell et al., PRL 119, 140602 (2017)
[3] A. Leymann et al., PRX 7, 021045 (2017); D. Vorberg, R. Ketzmerick, A. Eckardt, in preparation

16:30  17:00

Achilleas Lazarides
(MPIPKS Dresden)
Floquet manybody physics
I report on recent work on periodicallydriven (Floquet) manybody systems, focussing on the case where nontrivial phases (including a pispin glass or "discrete time crystal") are found.

17:00  17:30

Angelo Russomanno
(Scuola Normale Superiore Pisa and International Centre for Theroetical Physics Trieste)
Boundary time crystals
In this presentation I introduce {\it boundary timecrystals}. Here {\it continuous} timetranslation symmetry breaking occurs at the boundary (or generically in a macroscopic portion) of a manybody quantum system. I describe definition and properties, and then analyse in details a solvable model. I provide examples of other systems where boundary time crystalline phases can occur and underline the intimate connection to the emergence of a timeperiodic steady state in the thermodynamic limit.

17:30  18:00

Igor Mekhov
(University ParisSaclay (SPEC CEA), University of Oxford, St. Petersburg State University)
Open systems beyond dissipation: weak measurements and feedback control in manybody systems
Open dissipative systems have provided a mean to study manybody phenomena well beyond isolated systems obeying unitary evolution. The next step enriching physical picture is to exploit the quantum nature of the measurement process for preparing nontrivial manybody states, which can be then controlled using feedback. Such a setting includes the description of dissipation as a special case (by the ignorance of measurement results), but enables to achieve manybody states and phenomena, which are typical to neither closed systems described by Hamiltonians, nor open systems described by e.g. Lindblad master equation [1,2].
Considering ultracold bosons and fermions in optical lattices, we show that it is not only density variables that are accessible by quantum measurements of scattered light, but the matterphase variables (intersite bonds or links) as well [1]. We prove that the quantum backaction of weak global measurement constitutes a novel source of competitions in manybody systems [3], leading to novel effects: multimode oscillations of macroscopic superposition states, protection and breakup of fermion pairs [3], as well as generation of antiferromagnetic states [4]. Novel processes beyond the standard Hubbard models can be designed by the measurement, entering the field of nonHermitian (while being nondissipative) manybody physics: longrange correlated pair tunnelling and Ramanlike secondorder transitions beyond the typical quantum Zeno dynamics [1,5]. We show that the feedback control can drive the system to stable manybody strongly correlated phases [2].
[1] W. Kozlowski, S. F. CaballeroBenitez, and I. B. Mekhov, Scientific Rep. 7, 42597 (2017);
[2] G. Mazzucchi, S. F. CaballeroBenitez, D. A. Ivanov, and I. B. Mekhov, Optica (OSA) 3, 1213 (2016);
[3] G. Mazzucchi, W. Kozlowski, S. F. CaballeroBenitez, T. J. Elliott, and I. B. Mekhov, Phys. Rev. A 93, 023632 (2016);
[4] G. Mazzucchi, S. F. CaballeroBenitez, and I. B. Mekhov, Scientific Rep. 6, 31196 (2016);
[5] W. Kozlowski and I. B. Mekhov, Phys. Rev. A 94, 012123 (2016).

19:00  20:00

Dinner

20:00  21:30

Poster session (focus on odd numbers)
