Nucleation in finite topological systems during continuous metastable   quantum phase transitions
  Finite topological quantum systems can undergo continuous metastable quantum phase transitions to change their topological nature. Here we show how to nucleate the transition between ring currents and dark soliton states in a toroidally trapped Bose-Einstein condensate. An adiabatic passage to wind and unwind its phase is achieved by explicit global breaking of the rotational symmetry. This could be realized with current experimental technology. 
Oleksandr Fialko, Marie-Coralie Delattre, Joachim Brand and Andrey R.   Kolovsky
cond-mat.quant-gas