Parametric resonance phenomena in Bose-Einstein condensates: Enhanced quantum tunneling of coherent matter pulses

We investigate the quantum tunneling of a Bose-Einstein condensate confined in an optical trap. We show that periodic pulses of coherent matter are emitted from the trap by using an oscillating energy barrier. Moreover, the emitted fraction of condensed atoms strongly increases if the period of oscillation of the height of the energy barrier is in parametric resonance with the period of oscillation of the center of mass of the condensate inside the potential well. Our model is analyzed by numerically solving the nonpolynomial Schrodinger equation (NPSE), an effective one-dimensional equation which describes the macroscopic wave function of Bose condensates under transverse harmonic confinement. The range of validity of the NPSE is discussed and compared with that of the Gross-Pitaevskii equation.