Fast rotation of an ultra-cold Bose gas

TL;DR

This paper investigates the behavior of a Bose-Einstein condensate under rapid rotation, revealing unexpected vortex dynamics and surface density changes at high rotation frequencies.

Contribution

It demonstrates the ability to increase the rotation of a Bose gas beyond the trap frequency using a combined quadratic and quartic potential, and observes novel vortex phenomena.

Findings

Vortices become less visible at high rotation speeds.

Surface vortex density is lower than expected.

Rapid rotation induces dramatic changes in quantum gas appearance.

Abstract

We study the rotation of a $^{87}$Rb Bose-Einstein condensate confined in a magnetic trap to which a focused, off resonant gaussian laser beam is superimposed. The confining potential is well approximated by the sum of a quadratic and a quartic term which allows to increase the rotation frequency of the gas above the trap frequency. In this fast rotation regime we observe a dramatic change in the appearance of the quantum gas. The vortices which were easily detectable for a slower rotation become much less visible, and their surface density is well below the value expected for this rotation frequency domain. We discuss some possible tracks to account for this effect.