Dynamical instabilities of Bose-Einstein condensates at the band-edge in one-dimensional optical lattices

TL;DR

This paper investigates the dynamical instability of Bose-Einstein condensates at the band-edge in one-dimensional optical lattices, combining experiments with advanced numerical modeling to understand condensate depletion and thermalization.

Contribution

It demonstrates the limitations of the Gross-Pitaevskii equation and applies the truncated Wigner method for accurate modeling of instability phenomena.

Findings

Experimental observation of rapid condensate depletion

Gross-Pitaevskii equation fails to describe the instability

Truncated Wigner method accurately predicts thermalization processes

Abstract

We report on experiments that demonstrate dynamical instability in a Bose-Einstein condensate at the band-edge of a one-dimensional optical lattice. The instability manifests as rapid depletion of the condensate and conversion to a thermal cloud. We consider the collisional processes that can occur in such a system, and perform numerical modeling of the experiments using both a mean-field and beyond mean-field approach. We compare our numerical results to the experimental data, and find that the Gross-Pitaevskii equation is not able to describe this experiment. Our beyond mean-field approach, known as the truncated Wigner method, allows us to make quantitative predictions for the processes of parametric growth and thermalization that are observed in the laboratory, and we find good agreement with the experimental results.