Towards a Landau-Zener formula for an interacting Bose-Einstein   condensate
  We consider the Landau-Zener problem for a Bose-Einstein condensate in a linearly varying two-level system, for the full many-particle system as well and in the mean-field approximation. The many-particle problem can be solved approximately within an independent crossings approximation, which yields an explicit Landau-Zener formula. 
D. Witthaut, E. M. Graefe, and H. J. Korsch