We investigate the phase diagram of a two-species Bose-Hubbard model including a conversion term, by which two particles from the first species can be converted into one particle of the second species, and vice versa. The model can be related to ultracold atom experiments in which a Feshbach resonance produces long-lived bound states viewed as diatomic molecules. The model is solved exactly by means of quantum Monte Carlo simulations. We show that an “inversion of population” occurs, depending on the parameters, where the second species becomes more numerous than the first species. The model also exhibits an exotic incompressible “super-Mott” phase where the particles from both species can flow with signs of superfluidity, but without global supercurrent. We present two phase diagrams, one in the chemical potential, conversion plane, the other in the chemical potential, detuning plane.

• Received 18 October 2007

DOI:https://doi.org/10.1103/PhysRevA.77.013609