Superflow in a toroidal Bose-Einstein condensate: an atom circuit with a   tunable weak link
  We have created a long-lived (~ 40 s) persistent current in a toroidal Bose-Einstein condensate held in an all-optical trap. A repulsive optical barrier creates a tunable weak link in the condensate circuit, which can affect the current around the loop. Superflow stops abruptly at a barrier strength such that the local flow velocity exceeds a critical velocity. The measured critical velocity is consistent with dissipation due to the creation of vortex-antivortex pairs. This system is the first realization of an elementary closed-loop atom circuit. 
A. Ramanathan, K. C. Wright, S. R. Muniz, M. Zelan, W. T. Hill III, C.   J. Lobb, K. Helmerson, W. D. Phillips, and G. K. Ca...
cond-mat.quant-gas