Quantum Chaos in the Bose-Hubbard model
  We present a numerical study of the spectral properties of the 1D Bose-Hubbard model. Unlike the 1D Hubbard model for fermions, this system is found to be non-integrable, and exhibits Wigner-Dyson spectral statistics under suitable conditions. 
Andrey R. Kolovsky and Andreas Buchleitner