Coupled mode theory for Bose-Einstein condensates

Summary form only given. A system of interacting bosons confined within an external potential at zero temperature can be described by a macroscopic wave function having the meaning of an order parameter and satisfying the nonlinear Gross-Pitaevskii (GP) equation. In such a system, single-particle states form a set of nonlinear collective modes corresponding to the ground and higher-order (excited) macroscopic states of the Bose-Einstein condensate (BEC) in a trap. We analyse the mode coupling and intermodal population exchange in trapped BECs. We consider the BEC dynamics in a harmonic double-well potential, and derive the dynamical coupled-mode equations, valid for any value of the well separation. Our model can describe both the Josephson tunneling between weakly interacting condensates and effective Rabi oscillations in two component BECs.