Non-equilibrium classical and quantum fluids

NEQfluids24 : Non-equilibrium classical and quantum fluids

Grenoble (France)

Titles and abstracts

Mathias Albert

Title: Interaction effects in quantum kicked rotors

Abstract: The quantum kicked rotor is a Floquet system with a very rich phenomenology, from quantum chaos [1] to topological effects [2,3]. In particular, it displays a phenomenon called dynamical localisation, which is analogous to Anderson localisation but in momentum space [4]. In this talk, I will present non-trivial results induced by interactions in variants of this model. I will discuss first the breakdown of thermalisation in a non-linear version of this model due to superfluidity in momentum space [5]. Then, I will discuss the possibility to observe an Anderson transition in a kicked Lieb-Liniger model using exact solutions for three particles.

[1] F. Haake, Quantum signatures of chaos (1991).
[2] J. P. Dahlhaus et al., Phys. Rev. B 84, 115133 (2011).
[3] R. W. Bomantara et al., Phys. Rev. E 93, 022209 (2016).
[4] D. R. Grempel et al., Phys. Rev. A 29, 1639 (1984).
[5] S. Mu et al., EPL 140 50001 (2022).

Hugues Chaté

Title: TBA

Abstract: TBA

Rodolfo Cuerno

Title: Nonequilibrium critical dynamics: some upturns from surface kinetic roughening

Abstract: The collective properties that characterize dynamical complex systems often emerge from the interplay at comparable time scales between external driving and dissipation, in such a way that criticality holds without parameter tuning. An example is surface kinetic roughening, ubiquitous across system nature and physical scales to the extent that some of its main instances ---like the celebrated 1D Kardar-Parisi-Zhang (KPZ) universality class [1]--- are becoming relevant even to non-interfacial systems.

With a view on the rich structure recently unveiled by this universality class, we will address issues that may enhance our understanding of critical dynamics far from equilibrium. For instance, the extent to which critical exponent values identify the universality class and the roles at this that can be played by the statistics of fluctuations (including their symmetries and physical nature) and by the (type of) dynamic scaling ansatz that ensues. Examples will be drawn from recent work on KPZ-related systems, including Burgers [2,3] and Kuramoto-Sivashinsky models [4], or the KPZ equation without surface tension [5] or with columnar disorder [6].

[1] K. A. Takeuchi, Physica A 504, 77 (2018).
[2] E. Rodríguez-Fernández & R. Cuerno, Phys. Rev. E 99, 042108 (2019); ibid. 101, 052126 (2020).
[3] E. Rodríguez-Fernández & R. Cuerno, Phys. Rev. Res. 3, L012020 (2021).
[4] E. Rodríguez-Fernandez, S. N. Santalla, M. Castro, & R. Cuerno, Phys. Rev. E 106, 024802 (2022); arXiv:2208.00914v2.
[5] R. Gutiérrez & R. Cuerno, Phys. Rev. Res. 5, 023047 (2023); ibid. 6, 033324 (2024); Phys. Rev. E 110, L052201 (2024).

Félix Helluin

Title: Phase diagram and universal scaling regimes of two-dimensional exciton--polariton Bose--Einstein condensate.

Abstract: Exciton-polariton condensates offer a promising platform for observing non-equilibrium universal features within quantum fluids. By conducting extensive numerical simulations, we show that the effective nonlinearity of the condensate phase dynamics can be finely adjusted across a broad range. This allows one to probe three main universal regimes with parameters accessible in current experiments: the weakly nonlinear Edwards-Wilkinson (EW) regime, where the phase profile does not become rough ; the strongly non-linear Kardar-Parisi-Zhang regime, where the condensate phase fluctuations grow in a superdiffusive manner leading to roughening of the phase ; and a vortex-dominated phase emerging at stronger interactions, where both density and phase dynamics play significant roles.

Ref.: F. Helluin, D. Pinto-Dias, Q. Fontaine, S. Ravets, J. Bloch, A. Minguzzi, L. Canet, arXiv:2411.04311

Vivien Lecomte

Title: Hidden scaling regime at short lenghtscales in a model of random interface : a numerical approach

Abstract: Elastic interfaces display scale-invariant geometrical fluctuations at sufficiently large lengthscales. Their asymptotic static roughness then follows a powerlaw behavior, whose associated exponent provides a robust signature of the universality class to which they belong. Here we compute numerically the roughness of a one-dimensional elastic interface subject to both thermal fluctuations and a quenched disorder with a finite correlation length. We evidence the existence of a power-law regime at short lengthscales, hidden under thermal fluctuations. We determine the corresponding exponent ζ_dis and find numerical evidence supporting a value ζdis < 1. We discuss the implications of our findings for other systems, such as the Kardar–Parisi–Zhang equation and Burgers turbulence.

Joint work with Elisabeth Agoritsas, Nirvana Caballero and Thierry Giamarchi

Sébastien Lucas

Title: Dimensional crossover in localization of light

Abstract: In a dense and large ensemble of atoms, the atoms couple via the electromagnetic field and their individual atomic states hybridize into collective atomic states. These collective resonances can be largely de-tuned from the atomic resonance frequency and exhibit enhanced decay-rates (super-radiant states), lifetimes several orders of magnitude greater than the one of single atoms (sub-radiant states) and even Anderson localization. We study numerically the collective modes of ensemble of atoms randomly placed on a plane in the middle of a Fabry-Pérot cavity whose boundary conditions allow only for one TM propagative mode. Such geometry decouples the in-plane excitations (TM) from the out-of-plane excitations (TE), allowing to study the impact of the scalar or vectorial nature of the light on Anderson localization. Due to the cavity, the coupling between atoms via the TM modes resembles the one of a 2D scalar problem, with a near field dipole-dipole interaction inherited from the 3D nature of the problem. This allows to tune the effective dimensionality of the problem with the density of scatterers, giving rise to a localization transition. Additionally, although not able to support transport in an empty cavity, TE modes allow short range interaction between atoms that can restore transport at high enough densities, giving rise to a different localization transition.

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