Parametric resonant phenomena in Bose-Einstein condensates: Breaking of macroscopic quantum self-trapping

We analyze the periodic tunneling of a Bose-Einstein condensate in a double-well potential which has an oscillating energy barrier. We show that the dynamics of the Bose condensate critically depends on the frequency omega of the oscillating energy barrier. In the regime of periodic macroscopic quantum tunneling (PMQT) with frequency omega(J), the population imbalance of the condensate in the two wells can be enhanced under the condition of parametric resonance omega = 2omega(J). Instead, in the regime of macroscopic quantum self-trapping (MQST), we find that MQST can be reduced or suppressed under the condition of parametric resonance between the frequency omega of the energy barrier and the frequency omega(ST) of oscillation through the barrier of the very small fraction of particles which remain untrapped during MQST.