Spin-driven spatial symmetry breaking of spinor condensates in a   double-well
  The properties of an F=1 spinor Bose-Einstein condensate trapped in a double-well potential are discussed using both a mean-field two-mode approach and a simplified two-site Bose-Hubbard Hamiltonian. We focus in the region of phase space in which spin effects lead to a symmetry breaking of the system, favoring the spatial localization of the condensate in one well. To model this transition we derive, using perturbation theory, an effective Hamiltonian that describes N/2 spin singlets confined in a double-well potential. 
Marina Mel\'e-Messeguer, Simone Paganelli, Bruno Juli\'a-D\'iaz, Anna   Sanpera and Artur Polls
cond-mat.quant-gas