Collapse of a Bose condensate with attractive interactions

We examine the Gross-Pitaevskii (GP) model for Bose-Einstein condensates in parabolic traps with attractive interactions. The decay of metastable condensates is investigated by applying the instanton formalism to the GP field theory. Employing various dynamical trial states, we derive within a coherent state path integral approach a collective coordinate description in terms of the condensate radius, in agreement with (and extending) earlier results. We then solve numerically for the complete instanton field configuration and compare with the collective coordinate approach. Adjusting only the effective mass of the collective coordinate, the two schemes are then in good agreement. [S1050-2947(99)05701-7].