The slides of the talks are available below, by clicking on the links “[pdf]” next to the corresponding abstract

Wednesday 6th, September

08:30 | Registration | |

09:00 | Conference opening | |

09:10 | Carlo Barenghi | Types of quantum turbulence |

09:50 | Lucas Madeira | Characterization and universal scaling properties of a turbulent atomic superfluid: a new point of view |

10:30 | Sergey Nazarenko | Direct and inverse cascades in BEC Wave Turbulence |

11:10 | Coffee break | |

11:40 | Jere Mäkinen | Rotating quantum wave turbulence and onset of the Kelvin wave cascade |

12:20 | Matthew Davis | Nonequilibrium Transport in a Superfluid Josephson Junction Chain |

13:00 | Lunch | |

15:00 | Giacomo Roati | Engineering vortex matter in strongly-correlated superfluids |

15:40 | Natalia Berloff | Minimising Ising and XY Hamiltonians with Bose-Einstein condensates |

16:20 | Coffee break | |

16:40 | Tobias Holder | Vortices and para-hydrodynamics in ultraclean WTe2 flakes |

17:20 | Núria Ferrer | Greetings from Societat Catalana de Física |

17:30 | Alberto Antonio Gómez | Access to HPC resources for research acceleration |

17:50 | Posters & Drinks |

Thursday 7th, September

09:10 | Julian Léonard | Quantum simulations with optical lattices: quantum avalanches and fractional quantum Hall states |

09:50 | Päivi Törmä | Quantum Geometry in flat-band superconductivity, Bose-Einstein condensation, and light-matter interactions |

10:30 | Georg Bruun | Excitons as probes for moiré spin correlations: polarons and strings |

11:10 | Coffee break and group photo | |

11:40 | Thierry Giamarchi | Quantum Transport and Cold Atomic Gases |

12:20 | Jesper Levinsen | Exciton-polariton interactions and quasi-equilibrium condensates |

13:00 | Lunch | |

15:00 | Lauriane Chomaz | Quantum many-body states in magnetic atomic Bose gases and their dynamics |

15:40 | Selim Jochim | Rotating traps, a Laughlin wave function, and the emergence of fluid behavior |

16:20 | Coffee break | |

16:40 | Julian Schmitt | Compressibility and fluctuations of an optical quantum gas |

17:20 | Giacomo Lamporesi | Magnetism and bubble formation in coupled superfluid spin mixtures |

— | — | |

20:00 | Conference dinner |

Friday 8th, September

09:50 | Jean-Philippe Brantut | Phases and dynamics of a unitary Fermi gas in a high-finesse cavity |

10:30 | Anna Minguzzi | Emergent KPZ universality in one- and two-dimensional exciton-polariton condensates |

11:10 | Coffee break | |

11:40 | Thomas Gasenzer | Universal dynamics of rogue waves and instantons in a quenched spinor Bose condensate |

12:20 | Bruno Julià-Diaz | One dimensional lattice quantum droplets |

13:00 | Conference Conclusions |

## Abstracts

**1 – Carlo Barenghi**

Newcastle University

Types of quantum turbulence [pdf]

In the last years, experimental and theoretical studies have compared turbulence in ordinary viscous fluids (classical turbulence) and turbulence in quantum fluids (quantum turbulence). Remarkable similarities and differences have been found when comparing classical turbulence with turbulence in superfluid helium (bosonic He4 and fermionic He3). Recent progress in the study of quantum turbulence in atomic Bose-Einstein condensates has revealed that, when turbulent, these systems are unlike superfluid helium in many respects. The aim of this lecture is to summarize the evidence and to identify the different types of quantum turbulence which have been observed.

**2 – Vanderlei Bagnato**

**Lucas Madeira**

IFSC- University of São Paulo – Brazil and BME- Texas A&M University – USA

Characterization and universal scaling properties of a turbulent atomic superfluid: a new point of view [pdf]

In this presentation we will combine many of the experiments performed in Brazil relating to the production and characterization of a Bose Condensate of Rb atoms, driven far from equilibrium. Simulations demonstrated generation of solitons, vortices and waves in the sample. Using time of flight techniques, we measure the moment distribution, n(k, t) and from it we obtain the energy spectrum E (k, t), Scale length and the regions in -space characterized by constant flux. Most of the presentation will rely on a new vision to analyze the temporal evolution of the moment distribution related to the presence of a class of universality in the phenomenon. The problem is investigated on the basis of the theory of the existence of non-thermal fixed points in the system, introducing a few new features to it. A discussion around these aspects is offered. This work received support from FAPESP- program CEPID, CNPq and CAPES, all Brazilian agencies and had the participation of L. Madeira, A. Garcia-Orosco, P. Castilho, M. Moreno, L. Machado, G. Telles, H. A. J. Middleton-Spencer (visiting student) and P.E.S. Tavares. We appreciate collaboration with G. Roati, C. Barenghi and discussions with T. Gasenzer.

**3 – Sergey Nazarenko**

Institute de Physique de Nice, CNRS

Direct and inverse cascades in BEC Wave Turbulence [pdf]

When a BEC is driven out of equilibrium, density waves interact nonlinearly and trigger turbulent cascades. In a turbulent BEC, energy is transferred toward small scales by a direct cascade, whereas the number of particles displays an inverse cascade toward large scales. In this work, we study analytically and numerically the direct and inverse cascades in wave-turbulent BECs. We analytically derive the Kolmogorov-Zakharov spectra, including the log correction to the direct cascade scaling and the universal prefactor constants for both cascades. We test and corroborate our predictions using high-resolution numerical simulations of the forced-dissipated Gross-Pitaevskii model in a periodic box and the corresponding wave-kinetic equation. Theoretical predictions and data are in excellent agreement, without adjustable parameters.

**4 – Jere Mäkinen**

Aalto University

Rotating quantum wave turbulence and onset of the Kelvin wave cascade [pdf]

Rotating turbulence in classical ﬂuids can often be described as an ensemble of interacting inertial waves across a wide range of length scales. In contrast, in superfluids the spectrum of waves extends to microscopic scales as Kelvin waves on quantized vortices. I will discuss our experiments with rotating superﬂuid 3He-B, where inertial waves are excited at the largest scale by periodic modulation of the angular velocity. The main results include observation of dissipation-independent energy transfer to smaller scales via so-called quantum boundary layer, unique to superfluids, and the eventual onset of the Kelvin-wave cascade at the lowest temperatures.

**5 – Matthew Davis**

The University of Queensland [pdf]

Nonequilibrium Transport in a Superfluid Josephson Junction Chain

Recent experiments have studied nonequilibrium transport in a superfluid Josephson junction chain formed by loading a three-dimensional Bose-Einstein condensate into one-dimensional optical lattice [1,2]. We develop a beyond-mean-field multimode model for this system based on c-field theory that incorporates the effects of fluctuations and dissipation. We study the refilling dynamics following the deletion of population at a single site, and examine the experimental observation of negative differential conductivity [1]. We also analyse the bistable behaviour of the nonequilibrium steady states that emerge when dissipation is applied to a single site [2]. Our results are in quantitative agreement with observations [3,4], and illustrate the role of fluctuations in many-body systems that are far from equilibrium.

[1] R. Labouvie et al., Phys. Rev. Lett. 115, 050601 (2015)

[2] R. Labouvie et al., Phys. Rev. Lett. 116, 235302 (2016)

[3] M. T. Reeves and M. J. Davis, SciPost Phys. 15, 068 (2023)

[4] S. E. Begg et al., arXiv:2307.14590 (2023)

**6 – Giacomo Roati**

CNR-INO and LENS, Sesto Fiorentino Italy

Engineering vortex matter in strongly-correlated superfluids

We realize a novel programmable vortex platform in planar and homogeneous atomic Fermi superfluids [1]. We engineer on-demand vortex configurations and we track vortex trajectories. Our ultimate control on the vortex dynamics makes our platform the ideal “quantum laboratory” where to elucidate the intimate nature of vortex-driven instabilities, opening important prospects towards the understanding of out-of-equilibrium dynamics and of exotic vortex-matter phase transitions in strongly-correlated superfluids [2].

[1] W. J. Kwon et al., Nature, 600 (2021)

[2] D. Hernandez-Rajkov et al., arXiv:2303.12631 (2023)

**7 – Natalia Berloff**

University of Cambridge

Minimising Ising and XY Hamiltonians with Bose-Einstein condensates [pdf]

Unconventional computing architectures were proposed for numerous optical systems, including parametric oscillators, memristors, lasers and nanolasers, optoelectronic systems, photonic simulators, trapped ions, polariton and photon condensates. A promising approach to achieve computational supremacy over the classical von Neumann architecture explores classical and quantum hardware as Ising and XY machines. Gain-dissipative platforms such as the networks of optical parametric oscillators, coupled lasers and non-equilibrium Bose-Einstein condensates such as exciton-polariton or photon condensates use an approach to finding the global minimum of spin Hamiltonians which is different from quantum annealers or quantum computers. In my talk, I will discuss the principles of the operation of the devices based on such systems, the challenges they present, the role of vortices and the question of comparing different platforms’ performance.

**8 – Tobias Holder**

Weizmann Institute of Science

Vortices and para-hydrodynamics in ultraclean WTe2 flakes

Electron hydrodynamics has become a valuable tool in characterizing quantum materials. However, the formation of a whirlpool – arguably the most striking hydrodynamic phenomenon – has so far been elusive.I discuss recent results on ultrapure WTe2 flakes in which hydrodynamic vortices can be imaged using spatially resolved techniques. From the ab-initio perspective this observation is surprising, as one would rather expect ballistic transport. I show how this discrepancy can be resolved in a kinetic theory that incorporates weak surface scattering from the top and bottom surfaces, thereby leading to a novel para-hydrodynamic regime where ballistic and hydrodynamic mechanisms coexist.

**9 – Alberto Antonio Gómez**

Spanish Supercomputing Network (RES)

The Spanish Supercomputing Network (RES, from Red Española de Supercomputación), established in 2007 by the Spanish Ministry of Science and Education, is a Unique Scientific and Technical Infrastructure (ICTS) distributed throughout Spain, composed of 14 nodes interconnected with high-speed networks. The RES mission is to offer computing, data management and artificial intelligence services and resources to support the development of top-quality, cutting-edge and highly-innovative research projects, made available to the scientific community through competitive calls based on the scientific excellence of the proposals received.

**10 – Julian Léonard**

TU Wien

Quantum simulations with optical lattices: quantum avalanches and fractional quantum Hall states [pdf]

Quantum simulations with optical lattices offer the unique opportunity to experimentally address outstanding problems in many-body quantum physics. Quantum gas microscopy brings this effort to the ultimate level of single particle control. I will talk about our recent work on two topics: First, I will report on the observation of quantum avalanches, which challenge the notion of a stable many-body localized phase. Second, I will present our results on the realization of a fractional quantum Hall state, which we prepare through adiabatic quantum state engineering within the interacting Harper Hofstadter model. Our work gives new insights to non-equilibrium dynamics in disordered systems, and it provides a starting point for exploring entangled topological matter with ultracold atoms.

**11 – Päivi Törmä**

Aalto University

Quantum Geometry in flat-band superconductivity, Bose-Einstein condensation, and light-matter interactions [pdf]

We have found that superconductivity and superfluidity have a connection to quantum geometry. Using this theory, we have shown that superconductivity is possible also in a flat band where individual electrons would not move. Recently, we have shown that these results may be essential in explaining the observation of superconductivity in twisted bilayer graphene. We have also explored the effect of quantum geometry on Bose-Einstein condensation and shown that the quantum distance and quantum metric determine the stability of the condensate, and quantum fluctuations dominate over mean-field effects. Light-matter interactions become strongly enhanced by quantum geometry in flat bands.

**12 – Georg Bruun**

Aarhus University

Excitons as probes for moiré spin correlations: polarons and strings [pdf]

We show that excitons are sensitive probes for spin correlations of holes and electrons in a moiré lattice. Using a microscopic model for the moiré lattice combined with diagrammatic perturbation theory, charge and out-of-plane magnetic order are demonstrated to show up as umklapp scattering in the exciton spectrum, whereas the coupling spin correlations appear to second order in the exciton-electron scattering. Considering as examples ferro- and antiferromagnetic order and using a self-consistent Born approximation, this coupling is shown to lead to characteristic polaron and string peaks in the exciton spectrum.

**13 – Thierry Giamarchi**

Université de Genève

Quantum Transport and Cold Atomic Gases [pdf]

Quantum transport of a system which is between two reservoirs, at e.g. different chemical potentials, is one of the most common but also most important ways to put a quantum system out of equilibrium. Such a situation is relevant not only for charge transport but also for other transport properties such as spin transport or Hall transport for systems which are put under a (synthetic) magnetic field. I will discuss in this talk various realization of such quantum transport, and their theoretical solutions or challenges. These situations can be directly relevant for experimental situations encountered in cold atomic gases and I will discuss the contact with experimental realizations.

**14 – Jesper Levinsen**

Monash University

Exciton-polariton interactions and quasi-equilibrium condensates [pdf]

The Bogoliubov theory of weakly interacting Bose gases rests upon the assumption that nearly all bosons condense into the lowest quantum state. Here, we develop a generalized Bogoliubov theory for a driven-dissipative exciton-polariton condensate with an incoherent excitonic reservoir. We predict that interconversion between dark and bright excitons can lead to dynamical equilibrium, and that the non-Galilean-invariant nature of polaritons fundamentally modifies the energy and amplitudes of quasiparticle excitations. Our theory is supported by experiment, which directly detects the excitations of a polariton condensate. From the measurements, we extract the Bogoliubov amplitudes and show that they agree with our theory.

**15 – Lauriane Chomaz**

Heidelberg University

Quantum many-body states in magnetic atomic Bose gases and their dynamics

Quantum degenerate gases of highly magnetic atoms have opened new research avenues in which long-range anisotropic dipole-dipole interactions play a crucial role. In Bose gases, these interactions compete with the conventional short-range contact interactions. Fine control of this interaction competition through Feshbach resonances and of the gas geometry has led to the discovery of novel many-body quantum states and exotic dynamical behavior. In my talk I will present recent experimental results highlighting the specificity of quantum dynamics in gases of magnetic atoms and discuss future research directions that we plan to explore in my new group in Heidelberg.

**16 – Selim Jochim**

Heidelberg University

Rotating traps, a Laughlin wave function, and the emergence of fluid behavior [pdf]

In our quest to construct many body systems atom by atom, we are controlling the motional degree of atoms quantum by quantum in a close to harmonic trapping potential. Our newest addition to our toolbox is the ability to rotate a slightly elliptic potential in order to introduce angular momentum into the system. In this way we can prepare single atoms or molecules in a state with discrete angular momentum. Attempting to realize a many-body system we make the first step by introducing angular momentum to the relative motion of two atoms, effectively creating a Laughlin state, where the atoms minimize interaction. While so far we have no ability to realize a manipulate the atoms in a spin selective way, we use a coupling between center-of-mass and relative motion to create the Laughlin state. While we are still looking for ideas on how to create such states with larger numbers of atoms, we have already studied how collective modes in emerge as the system size is increased. We clearly observe a quadrupole mode with about 20 atoms, indicating fluid behavior. Another observable for fluid behavior is elliptic flow that has been employed heavily in heavy-ion physics. In a 2-dimensional configuration we observe elliptic flow for as few as 10 atoms.

**17- Julian Schmitt**

Institute of Applied Physics, University of Bonn

Compressibility and fluctuations of an optical quantum gas [pdf]

Quantum gases provide a test bed to explore phases of matter, for example, by probing their susceptibilities or fluctuations. For gases of material particles, studies of the mechanical response are well established, but for optical quantum gases, they have so far remained elusive. In my talk, I will discuss measurements of the compressibility of a uniform two-dimensional quantum gas of photons inside a dye-filled microcavity, from which the equation of state for the optical medium is obtained. Finally, I will also report on more recent work verifying a fluctuation-dissipation relation and a non-Hermitian transition in photon Bose-Einstein condensates.

**18 – Giacomo Lamporesi**

Pitaevskii Center for Bose-Einstein Condensation, Trento, Italy

Magnetism and bubble formation in coupled superfluid spin mixtures

In the presence of coherent coupling, superfluid spin mixtures can exhibit magnetic properties.

We show that a particular combination of spin states of sodium allows to observe the transition from para- to ferromagnetic behavior of the superfluid, characterized by ground state bifurcation, by hysteresis and divergence of susceptibility and magnetic fluctuations [1].

The same system is also used to study how a macroscopic system, prepared in a metastable magnetic state, naturally decays to the absolute ground state via bubble formation through macroscopic tunneling, in analogy with false vacuum decay mechanism, predicted in field theory [2].

[1] R. Cominotti et al., PRX 13, 021037 (2023)

[2] A. Zenesini et al., arXiv:2305.05225 (2023)

**19 – Jean Philippe Brantut**

EPFL – École Polytechnique Fédérale de Lausanne

Phases and dynamics of a unitary Fermi gas in a high-finesse cavity [pdf]

I will present a set of experiments in which a unitary Fermi gas is placed in a high-finesse optical cavity. Upon driving the system from the side, we engineer a photon-mediated long-range interaction on top of the resonant contact interaction and observe the formation of a density-wave ordered state. We then explore the dynamics of the transition by quenching across the boundary instantaneously or using a finite speed ramp. In both cases the onset of density-wave obeys a universal law throughout the BEC-BCS crossover. Our work shows light on the interplay of charge order with superfluidity in strongly correlated matter.

**20 – Anna Minguzzi**

CNRS, Grenoble

Emergent KPZ universality in one- and two-dimensional exciton-polariton condensates

In driven-dissipative systems displaying macroscopic quantum coherence, as exciton polariton condensates under incoherent pumping, under specific conditions, the condensate phase dynamics can be mapped to the stochastic Kardar-Parisi-Zhang (KPZ) equation describing the growth and roughness of classical interfaces.

For one-dimensional excitons polaritons, I will report on our common theory-experimental work demonstrating the emergence of KPZ universality from the measurement of KPZ space-time scaling laws, combined with a theoretical analysis that reveals other key signatures of this universality class as the probability distribution. I will then provide the full phase diagram of 1D excitons polaritons, identifying three other regimes emerging respectively at large interactions, noise or pump: soliton patterned, phase-slips dominated and reservoir textured one.

In the two-dimensional case, where KPZ universality competes with the emergence of vortices, I will report on our study revealing the emergenze of KPZ universality on a lattice. Our studies highlight the rich phase diagram of non-equilibrium polariton condensates and the fundamental differences with their equilibrium counterparts.

References

[1] Q. Fontaine et al, Nature 608, 687–691 (2022)

[2] K. Deligiannis et al, Phys. Rev. Research 4, 043207 (2022)

[3] F. Vercesi et al, arXiv:2307.15664

**21 – Thomas Gasenzer**

Heidelberg University

Universal dynamics of rogue waves and instantons in a quenched spinor Bose condensate [pdf]

Isolated systems far from equilibrium may exhibit universal scaling dynamics near a non-thermal fixed point. We find universal dynamics connected with the occurrence of extreme wave excitations in a spinor Bose gas, which propagate in an effectively random potential [1]. As a result of these rogue waves forming caustics, real-time instanton defects appear in the Larmor phase of the spin-1 system as quantum vortices in space and time. Our results have a strong relevance for understanding pattern coarsening from first principles and potential implications for far-from-equilibrium dynamics ranging from the early universe to geophysical dynamics and micro physics.

[1] I. Siovitz et al., arXiv:2304.09293

**22 – Bruno Julià-Diaz**

Universitat de Barcelona

One dimensional lattice quantum droplets

Bosonic mixtures loaded in one dimensional optical lattices feature a number of interesting quantum phases which have been recently described [1] and explained with a dimerized model [2]. In particular we demonstrated the existence of liquid and gaseous phases of both atoms and dimers, providing a system where dimerization and liquefaction of an exotic quantum liquid can be studied in great detail. In a recent work, we have extended the study to imbalanced situations, showing that the quantum droplets manage to sustain a small particle imbalance, resulting in an effective magnetization [3].

[1] I Morera, GE Astrakharchik, A Polls, B Juliá-Díaz, Physical Review Research 2 (2), 022008 (2020)

[2] I Morera, GE Astrakharchik, A Polls, B Juliá-Díaz, Physical Review Letters 126 (2), 023001 (2021)

[3] Jofre Vallès-Muns, Ivan Morera, Grigori E Astrakharchik, Bruno Juliá-Díaz, arXiv:2306.12283 (2023)

**23 – Nuria Ferrer**

Societat Catalana de Física [pptx]