Formation of granular structures in trapped Bose-Einstein condensates under oscillatory excitations

TL;DR

This paper investigates the formation of granular, fog-like spatial structures in trapped Bose-Einstein condensates under oscillatory excitations, revealing a new metastable state distinct from quantum turbulence.

Contribution

It provides experimental and numerical evidence of a novel granular structure in Bose-Einstein condensates, expanding understanding of nonequilibrium quantum states.

Findings

Observation of granular fog-like structures in BECs

Identification of long-lived, metastable droplets within the condensate

Distinction between granular structures and wave turbulence states

Abstract

We present experimental observations and numerical simulations of nonequilibrium spatial structures in a trapped Bose-Einstein condensate subject to oscillatory perturbations. In experiment, first, there appear collective excitations, followed by quantum vortices. Increasing the amount of the injected energy leads to the formation of vortex tangles representing quantum turbulence. We study what happens after the regime of quantum turbulence, with increasing further the amount of injected energy. In such a strongly nonequilibrium Bose-condensed system of trapped atoms, vortices become destroyed and there develops a new kind of spatial structure exhibiting essentially heterogeneous spatial density. The structure reminds fog consisting of high-density droplets, or grains, surrounded by the regions of low density. The grains are randomly distributed in space, where they move. They live sufficiently long time to be treated as a type of metastable objects. Such structures have been observed in nonequilibrium trapped Bose gases of $^{87}$Rb, subject to the action of alternating fields. Here we present experimental results and support them by numerical simulations. The granular, or fog structure is essentially different from the state of wave turbulence that develops after increasing further the amount of injected energy.