Nonlinear enhancement of the fractal structure in the escape dynamics of Bose-Einstein condensates

We consider the escape dynamics of an ensemble of Bose-Einstein-condensed atoms from an optical-dipole trap consisting of two overlapping Gaussian wells. Earlier theoretical studies (based on a model of quantum evolution using ensembles of classical trajectories) predicted that self-similar fractal features could be visible in this system by measuring the escaping flux as a function of time for varying initial conditions. Here, direct numerical quantum simulations show the clear influence of quantum interference on the escape data. Fractal features are still evident in the data, albeit with interference fringes superposed. Furthermore, the nonlinear influence of atom-atom interactions is also considered, in the context of the (2+1)-dimensional Gross-Pitaevskii equation. Of particular note is that an attractive nonlinear interaction enhances the resolution of fractal structures in the escape data. Thus, the interplay between nonlinear focusing and dispersion results in dynamics that resolve the underlying classical fractal more faithfully than the noninteracting quantum (or classical) dynamics.