Beyond standard two-mode dynamics in bosonic Josephson junctions

We examine the dynamics of a Bose-Einstein condensate in a symmetric double-well potential for a broad range of nonlinear couplings. We demonstrate the existence of a region, beyond those of Josephson oscillations and self-trapping, which involves the dynamical excitation of the third mode of the double-well potential. We develop a simple semiclassical model for the coupling between the second and third modes that describes very satisfactorily the full time-dependent dynamics. Experimental conditions are proposed to probe this phenomenon.