Experiments with a superfluid BEC ring

Abstract

This dissertation presents multiple results of our experiments with ring-shaped 23Na Bose-Einstein condensates. First, we measure the effect of temperature on the lifetime of quantized, persistent currents. We find that the persistent current lifetime decreases when the temperature is increased. We also extract the critical velocity by measuring the size of hysteresis loops. The critical velocity is found to be a strong function of temperature. Second, we implement a new technique of measuring the circulation state of a persistent current in-situ, which is minimally-destructive. This technique uses the Doppler effect. We then measure the current-phase relation of a weak link inserted in the ring-shaped superfluid and measure the excitation spectrum of the ring-shaped superfluid. Finally, we study the dynamics of rapidly expanding rings, and explore the analogy between our experimental system and the expansion of the universe.