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 doublewell potential which has an oscillating energy barrier. We show that the dynamics of the Bose condensate critically depends on the frequency ω of the oscillating energy barrier. In the regime of periodic macroscopic quantum tunneling (PMQT) with frequency ωJ , the population imbalance of the condensate in the two wells can be enhanced under the condition of parametric resonance ω = 2ωJ . Instead, in the regime of macroscopic quantum selftrapping (MQST), we find that MQST can be reduced or suppressed under the condition of parametric resonance between the frequency ω of the energy barrier and the frequency ωST of oscillation through the barrier of the very small fraction of particles which remain untrapped during MQST.