Decay of rotational flow of a Bose-Einstein condensate in an optical toroidal potential

An interacting Bose-Einstein Condensate (BEC) is expected to exhibit superfluidity, and persistent currents in a magnetically trapped, toroidal shaped BEC have been seen lasting up to 10 seconds [1]. We have recently performed experiments in a ring-shaped optical dipole trap, formed by the combination of a Laguerre-Gaussian beam intersecting a light sheet at normal incidence. We use evaporative cooling to create a quasi-2D, ring-shaped BEC. We induce rotational flow by transferring orbital angular momentum of light to the atoms [1]. The flow was observed to decay very rapidly, in less than a rotation period. We are concurrently investigating if the rapid decay is due to inhomogeneities in the optical potential or due to the quasi-2D character of the BEC. [1] C. Ryu, M. F. Andersen, P. Clad\'{e}, Vasant Natarajan, K. Helmerson, and W. D. Phillips, Physical Review Letters, 99 260401 (2007).