Abstract

The Kibble-Zurek mechanism (KZM) describes the spontaneous formation of defects in systems that cross a second-order phase transition at a finite rate.  The mechanism, first proposed in the context of cosmology, is ubiquitous in nature and regards both classical and quantum phase transitions.  We will report on the observation of the KZM on ultracold atoms which are rapidly cooled across the BEC phase transitions.  The defects of the order parameter, imprinted via the KZM, evolve into solitonic vortices.  Clear signatures of the nature of such excitations are the twisted planar density depletion around the vortex line, observed after ballistic expansion, and the double dislocation in the interference pattern obtained through homodyne techniques.  Both methods allow us to determine the sign of the quantized circulation.  Experimental observations agree with numerical simulations.  These solitonic vortices show a very long lifetime.