Superfluid atom circuits

Persistent currents are a hallmark of both superfluidity and superconductivity. Just as a current in a superconducting circuit will flow forever, if a current is created in a superfluid Bose-Einstein condensate, the flow will not decay as long as the current is below a critical value. Using a ring-shaped Bose-Einstein Condensate we have created a superfluid “atom circuit” that supports long-lived persistent currents. A laser beam is used as a barrier across one side of the torus to create a tunable “weak link” in the condensate circuit and can be used to control the current around the loop. By rotating the weak link at low rotation rates, we have observed phase slips between well-defined, quantized, current states, and have demonstrated that the system exhibits hysteresis. This behavior is analogous to that of a weak link in a superconducting loop. Recently, we have also implemented a technique that allows us to directly measure the current-phase relationship of the weak-link. In electronic circuits, hysteresis plays in important role, particularly in applications like memory and digital noise filters, it's possible in future "atomtronic" circuits, our device could possibly play a similar role.