  The ground state of Bose-Einstein condensates with attractive particle
interaction is metastable. One of the decay mechanisms of the condensate is a
collapse by macroscopic quantum tunneling, which can be described by the bounce
trajectory as solution of the time-dependent Gross-Pitaevskii equation in
imaginary time. For condensates with an electromagnetically induced
gravity-like interaction the bounce trajectory is computed with an extended
variational approach using coupled Gaussian functions and simulated numerically
exact within the mean-field approach on a space-time lattice. It is shown that
the variational computations converge very rapidly to the numerically exact
result with increasing number of Gaussians. The tunneling rate of the
condensate is obtained from the classical action and additional parameters of
the bounce trajectory. The converged variational and numerically exact results
drastically improve by several orders of magnitude the decay rates obtained
previously with a simple variational approach using a single Gaussian-type
orbital for the condensate wave function.
