Observation of persistent flow of a Bose-Einstein condensate in a toroidal trap

TL;DR

This paper reports the first observation of long-lasting, quantized persistent flow in a Bose-Einstein condensate confined in a toroidal trap, demonstrating superfluidity and vortex dynamics.

Contribution

It presents experimental evidence of persistent superfluid flow in a toroidal BEC, including creation of flow with multiple angular momentum units and vortex splitting phenomena.

Findings

Flow persists up to 10 seconds without decay.

Stable flow requires a multiply-connected trap geometry.

Flow with two units of angular momentum splits into vortices when geometry changes.

Abstract

We have observed the persistent flow of Bose-condensed atoms in a toroidal trap. The flow persists without decay for up to 10 s, limited only by experimental factors such as drift and trap lifetime. The quantized rotation was initiated by transferring one unit, $\hbar$, of the orbital angular momentum from Laguerre-Gaussian photons to each atom. Stable flow was only possible when the trap was multiply-connected, and was observed with a BEC fraction as small as 15%. We also created flow with two units of angular momentum, and observed its splitting into two singly-charged vortices when the trap geometry was changed from multiply- to simply-connected.