Quantum kinetics of quenched two-dimensional Bose superfluids

TL;DR

This paper develops a quantum kinetic framework to analyze the non-equilibrium dynamics of 2D Bose superfluids after a quench, revealing limitations of quasi-particle descriptions in such scenarios.

Contribution

It introduces a quantum hydrodynamic and Keldysh formalism to derive kinetic equations for phonons in 2D Bose gases, connecting theory with recent experimental observations.

Findings

Quasi-particle descriptions become inaccurate in 2D non-equilibrium dynamics.

Derived kinetic equations describe phonon distributions post-quench.

Results highlight the importance of collective effects over independent quasi-particles.

Abstract

We study theoretically the non-equilibrium dynamics of a two-dimensional (2D) uniform Bose superfluid following a quantum quench, from its short-time (prethermal) coherent dynamics to its long-time thermalization. Using a quantum hydrodynamic description combined with a Keldysh field formalism, we derive quantum kinetic equations for the low-energy phononic excitations of the system and characterize both their normal and anomalous momentum distributions. We apply this formalism to the interaction quench of a 2D Bose gas and study the ensuing dynamics of its quantum structure factor and coherence function, both recently measured experimentally. Our results indicate that in two dimensions, a description in terms of independent quasi-particles becomes quickly inaccurate and should be systematically questioned when dealing with non-equilibrium scenarios.