Detection of vorticity in Bose-Einstein condensed gases by matter-wave   interference
  A phase-slip in the fringes of an interference pattern is an unmistakable characteristic of vorticity. We show dramatic two-dimensional simulations of interference between expanding condensate clouds with and without vorticity. In this way, vortices may be detected even when the core itself cannot be resolved. 
Eric L. Bolda and Dan F. Walls