Superflow in a Toroidal Bose-Einstein Condensate: An Atom Circuit with a Tunable Weak Link

TLDR

A repulsive optical barrier across one side of the toroidal condensate creates a tunable weak link that modulates the circulating superflow. The experiment demonstrates a long‑lived (~40 s) persistent current that abruptly ceases when the barrier induces a local flow velocity exceeding a critical value, with the critical velocity matching vortex–antivortex pair dissipation, marking the first closed‑loop atom circuit.

Abstract

We have created a long-lived ($\ensuremath{\approx}40\text{ }\text{ }\mathrm{s}$) persistent current in a toroidal Bose-Einstein condensate held in an all-optical trap. A repulsive optical barrier across one side of the torus creates a tunable weak link in the condensate circuit, which can affect the current around the loop. Superflow stops abruptly at a barrier strength such that the local flow velocity at the barrier exceeds a critical velocity. The measured critical velocity is consistent with dissipation due to the creation of vortex-antivortex pairs. This system is the first realization of an elementary closed-loop atom circuit.