Coupled-mode theory for Bose-Einstein condensates - art. no. 031601

We apply the concepts of nonlinear guided-wave optics to a Bose-Einstein co ndensate (BEC) trapped in an external potential. As an example, we consider a parabolic double-well potential and derive coupled-mode equations for th e complex amplitudes of the BEC macroscopic collective modes. Our equations describe different regimes of the condensate dynamics, including the nonli near Josephson effect for any separation between the wells. We demonstrate macroscopic self-trapping for both repulsive and attractive interactions, a nd confirm our results by direct numerical solution of the Gross-Pitaevskii -equation.