A rapidly expanding Bose-Einstein condensate: an expanding universe in the lab

TL;DR

This paper investigates the dynamics of a rapidly expanding ring-shaped Bose-Einstein condensate, revealing phenomena analogous to cosmological expansion, including excitation redshifting, topological defect formation, and stochastic persistent currents.

Contribution

It provides a combined experimental and theoretical analysis of BEC expansion, highlighting cosmological analogies and nonlinear excitation dynamics not previously explored.

Findings

Expansion redshifts long-wavelength excitations

Production of solitons, vortices, and azimuthal phonons

Observation of stochastic persistent currents

Abstract

We study the dynamics of a supersonically expanding ring-shaped Bose-Einstein condensate both experimentally and theoretically. The expansion redshifts long-wavelength excitations, as in an expanding universe. After expansion, energy in the radial mode leads to the production of bulk topological excitations -- solitons and vortices -- driving the production of a large number of azimuthal phonons and, at late times, causing stochastic persistent currents. These complex nonlinear dynamics, fueled by the energy stored coherently in one mode, are reminiscent of a type of "preheating" that may have taken place at the end of inflation.