Quantum effects on the dynamics of a two-mode atom-molecule Bose-Einstein condensate - art. no. 063611

We study the system of coupled atomic and molecular condensates within the two-mode model and beyond mean-field theory. Large-amplitude atom-molecule coherent oscillations are shown to be damped by the rapid growth of fluctua tions near the dynamically unstable molecular mode. This result contradicts earlier predictions about the recovery of atom-molecule oscillations in th e two-mode limit. The frequency of the damped oscillation is also shown to scale as rootN/1nN with the total number of atoms N, rather than the expect ed pure N scaling. Using a linearized model, we obtain analytical expressio ns for the initial depletion of the molecular condensate in the vicinity of the instability, and show that the important effect neglected by mean-fiel d theory is an initially nonexponential "spontaneous" dissociation into the atomic vacuum. Starting with a small population in the atomic mode, the in itial dissociation rate is sensitive to the exact atomic amplitudes, with t he fastest (superexponential) rate observed for the entangled state formed by spontaneous dissociation.