Strongly nonequilibrium Bose-condensed atomic systems

TL;DR

This paper explores the complex spatial structures and turbulence phenomena in strongly perturbed Bose-Einstein condensates, including vortices, vortex tangles, droplets, and wave turbulence, supported by experimental and numerical evidence.

Contribution

It provides a detailed analysis of nonequilibrium spatial structures in Bose condensates under strong perturbations, highlighting the formation of droplets and wave turbulence as new phenomena.

Findings

Observation of quantum vortices and vortex tangles.

Identification of high-density droplets as metastable structures.

Transition to wave turbulence destroying the condensate.

Abstract

A trapped Bose-Einstein condensate, being strongly perturbed, exhibits several spatial structures. First, there appear quantum vortices. Increasing the amount of the injected energy leads to the formation of vortex tangles representing quantum vortex turbulence. Continuing energy injection makes the system so strongly perturbed that vortices become destroyed and there develops another kind of spatial structures with essentially heterogeneous spatial density. These structures consist of high-density droplets, or grains, surrounded by the regions of low density. The droplets are randomly distributed in space, where they can move; however they live sufficiently long time to be treated as a type of metastable creatures. Such structures have been observed in nonequilibrium trapped Bose gases of $^{87}$Rb subject to the action of an oscillatory perturbation modulating the trapping potential. Perturbing the system even stronger transforms the droplet structure into wave turbulence, where Bose condensate is destroyed. Numerical simulations are in good agreement with experimental observations.