Quantum phase transition of Bose-Einstein condensates on a ring   nonlinear lattice
  We study the phase transitions in a one dimensional Bose-Einstein condensate on a ring whose atomic scattering length is modulated periodically along the ring. By using a modified Bogoliubov method to treat such a nonlinear lattice in the mean field approximation, we find that the phase transitions are of different orders when the modulation period is 2 and greater than 2. We further perform a full quantum mechanical treatment based on the time-evolving block decimation algorithm which confirms the mean field results and reveals interesting quantum behavior of the system. Our studies yield important knowledge of competing mechanisms behind the phase transitions and the quantum nature of this system. 
Zheng-Wei Zhou, Shao-Liang Zhang, Xiang-Fa Zhou, Guang-Can Guo,   Xingxiang Zhou, Han Pu
cond-mat.quant-gas