Improved variational approach to the two-site Bose-Hubbard model
  An improved variational ansatz is proposed to capture the most striking properties of the ground state of a slightly biased attractive two-site Bose-Hubbard Hamiltonian. Our ansatz, albeit its simplicity, is found to capture well the exact properties of the ground state for a wide variety of model parameters, in particular the fragmentation occurring before the formation of cat-like states and also the formation of strongly correlated cat-like states. 
Marina Mel\'e-Messeguer, Bruno Juli\'a-D\'iaz and Artur Polls
cond-mat.quant-gas