Transport of the repulsive Bose–Einstein condensate in a double-well trap: interaction impact and relation to the Josephson effect

Abstract

Two aspects of the transport of a repulsive Bose–Einstein condensate (BEC) in a double-well trap are inspected: The impact of the interatomic interaction and the analogy with the Josephson effect. The analysis employs a numerical solution of a 3D time-dependent Gross–Pitaevskii equation for a total order parameter covering the whole trap. The population transfer is driven by a time-dependent shift of a barrier separating the left and right wells. The sharp and soft profiles of the barrier velocity are tested. The evolution of the relevant characteristics, involving phase differences and currents, is inspected. It is shown that the repulsive interaction substantially supports the transfer making it possible (i) in a wide velocity interval and (ii) three orders of magnitude faster than in the ideal BEC. The transport can be approximately treated as the dc Josephson effect. The dual origin of the critical barrier velocity (break of the adiabatic following and dc/ac transition) is discussed. Following the calculations, the robustness of the transport (dc) crucially depends on the interaction and barrier velocity profile. Only soft profiles which minimize undesirable dipole oscillations are acceptable.