Condensation dynamics in a quantum-quenched Bose gas

TL;DR

This paper investigates how a quantum quench affects the condensation process in a Bose gas, revealing non-equilibrium dynamics, a two-step growth process, and a crossover to classical relaxation, supported by a simple equation of state.

Contribution

It provides experimental evidence of non-equilibrium condensation dynamics and demonstrates the transition from quantum to classical relaxation in a quenched Bose gas.

Findings

Observation of isoenergetic evolution after quenching

Clear separation between temperature and condensate growth dynamics

Crossover from quantum to classical relaxation regimes

Abstract

By quenching the strength of interactions in a partially condensed Bose gas we create a "super-saturated" vapor which has more thermal atoms than it can contain in equilibrium. Subsequently, the number of condensed atoms ($N_0$) grows even though the temperature ($T$) rises and the total atom number decays. We show that the non-equilibrium evolution of the system is isoenergetic and for small initial $N_0$ observe a clear separation between $T$ and $N_0$ dynamics, thus explicitly demonstrating the theoretically expected "two-step" picture of condensate growth. For increasing initial $N_0$ values we observe a crossover to classical relaxation dynamics. The size of the observed quench-induced effects can be explained using a simple equation of state for an interacting harmonically-trapped atomic gas.