Thermalization of a weakly interacting Bose gas in a disordered trap

TL;DR

This study demonstrates that a weakly interacting Bose gas in a disordered trap can undergo thermalization through disorder-induced relaxation, even in the regime where Anderson localization dominates, with evidence from entropy maximization and recurrence phenomena.

Contribution

It reveals that disorder can induce thermalization in a Bose gas in the Anderson localization regime, extending previous findings to a new parameter space.

Findings

Bose gas exhibits relaxation to equilibrium in the Anderson localization regime.

Entropy maximization occurs at thermodynamic equilibrium.

Fermi-Pasta-Ulam-Tsingou recurrence observed in the system.

Abstract

Previously we numerically showed that thermalization can occur in an oscillating Bose-Einstein condensate (BEC) with a disordered harmonic trap when healing length $\xi$ of the condensate is shorter than the correlation length $\sigma_{D}$ of the disorder [see, for example, the experiment reported in Phys. Rev. A \textbf{82}, 033603 (2010)]. In this work, we investigate the weakly interacting or Anderson localization regime $\xi>\sigma_{D}$ and show that the oscillating BEC can also exhibit a relaxation process from nonequilibrium to equilibrium. In such an isolated quantum system, energy and particle number are conserved and the irreversible evolution towards thermodynamic equilibrium is induced by the disorder. The thermodynamic equilibrium is evidenced by the maximized entropy $S\left[n_{k}\right]$ in which the waveaction spectrum $n_{k}$ follows the Rayleigh-Jeans distribution. Besides, unlike a monotonic irreversible process of thermalization to equilibrium, the Fermi-Pasta-Ulam-Tsingou recurrence arises in this system, manifested by the oscillation of the non-equilibrium entropy.