Non-equilibrium pre-thermal states in a two-dimensional photon fluid

Abstract

Thermalization is the dynamical process by which a many-body system evolves toward a thermal equilibrium state that maximizes its entropy. In certain cases, however, the establishment of thermal equilibrium is significantly slowed down and a phenomenon of pre-thermalization can emerge. It describes the initial relaxation toward a quasi-steady state after a perturbation. While having similar properties to their thermal counterparts, pre-thermal states exhibit a partial memory of initial conditions. Here, we observe the dynamical formation of a pre-thermal state in a non-equilibrium, two-dimensional (2D) fluid of light after an interaction quench. Direct measurements of the fluid's first-order correlation function reveal the spontaneous emergence of long-range algebraic correlations spreading within a light-cone, providing a clear signature of a quasi steady-state strongly similar to a 2D thermal superfluid. Detailed experimental characterization of the algebraic order is presented and a partial memory of the initial conditions is demonstrated, in agreement with recent theoretical predictions. Furthermore, by a controlled increase of the fluid fluctuations, we unveil a cross-over from algebraic to short-range (exponential) correlations, analogous to the celebrated Kosterlitz-Thouless transition observed at thermal equilibrium. These results suggest the existence of non-equilibrium precursors for thermodynamic phase transitions.

References in corpus (5)

• Quantum fluids of light
• Experimental Observation of a Generalized Gibbs Ensemble
• Extension of Bogoliubov theory to quasi-condensates
• Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas
• First-order spatial coherence measurements in a thermalized two-dimensional photonic quantum gas

Cited by in corpus (15)

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• Quantum Simulations with Bilayer 2D Bose Gases in Multiple-RF-dressed Potentials
• Dynamical emergence of a Kosterlitz-Thouless transition in a disordered Bose gas following a quench
• Paraxial fluids of light
• Key Observable for Linear Thermalization
• Low-energy prethermal phase and crossover to thermalization in nonlinear kicked rotors
• Dynamical phase transition of light in time-varying nonlinear dispersive media
• From inverse-cascade to sub-diffusive dynamic scaling in driven disordered Bose fluids
• Anomalous Landau damping and algebraic thermalization in two-dimensional superfluids far from equilibrium
• Coarsening of binary Bose superfluids: an effective theory
• Critical speed of a binary superfluid of light
• Spatio-temporal equilibrium thermodynamics of guided optical waves at positive and negative temperatures