Persistent current decay in an atomic ring trap

The motion of quantized vortices is of fundamental importance in different phenomena in condensed matter physics such as the resistive behaviour of superconductors or many other dissipative collective phenomena in superfluids. In particular, here we investigate theoretically their role on the decay of persistent current in ring-shaped atomic superfluids and in the presence of a small defect. In our studies, we model a recent experiment of ⁶Li at LENS in the limit of Bose-Einstein condensate of molecules. The numerical simulations are performed at T=0 by solving the Gross-Pitaevskii equation. A finite circulation state is excited by imprinting a phase in the equilibrium condensate wavefunction. In the absence of the defect, the current is persistent and the superflow is dissipatonless up to a maximum circulation. When a small defect instead is introduced, there is a critical velocity, i.e. a critical circulation, at which the vortices are emitted into the superfluid causing phase slips and thus a transition of the quantized initial circulation states to lower values (i.e. a decay of the current in time). We then give a microscopic description of such mechanism and its dependence on defect parameters and circulation state.