CM - AMO SEMINAR | Studying Superfluidity Using 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.  Both the strength of the perturbation and the temperature of the condensate affect the locations of these transitions, which can exhibit ferromagnetic-like hysteresis in certain regimes.  The combination of the ring and rotating perturbation form a circuit, which is analogous to an rf superconducting quantum interference device (SQIUD).  The rf-SQUID is 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, which allow us to study critical velocities and resistive flow in superfluids.  These experiments shed new light onto the details of quantum transport and superfluidity and may pave the way for new ‘atomtronic’ devices.