Studying superfluidity in cold-atom circuits

Superfluidity, or flow without resistance, is a macroscopic quantum effect that is present in a multitude of systems, including liquid helium, superconductors, and ultra-cold atomic gases.  Here, I will present our work studying superfluid flow in a Bose-Einstein condensate (BEC) of sodium atoms.  By manipulating optical potentials, we are able to form BECs into any shape, including rings and targets.  Ring condensates are unique in that they can support quantized, persistent currents.  We drive transitions between persistent current states using a rotating perturbation, or weak link.  This ring and rotating potential form a circuit, which is analogous to an rf superconducting quantum interference device (SQIUD).  Our circuit shows the essential features of an rf-SQUID, including tunable transitions between quantized persistent current states and hysteresis.  Such features make an rf-SQUID a sensitive magnetometer; by analogy, our device could act as a rotation sensor.  In addition to these experiments, we have also realized other geometries such as a dumbbell and a dc-SQUID, that allow us to study critical velocities and resistive flow in superfluids.  These, and similar experiments with tunable geometries, shed new light onto the details of quantum transport and superfluidity, and may pave the way for new ‘atomtronic’ devices.