Output coupling of Bose condensates from atomic tunnel arrays: a numericalstudy

We present an extensive numerical study of the transport properties of an i nteracting Bose-Einstein condensate subject to the forces induced by a peri odic potential and by gravity. This system models a mode-locked, pulsed las er of matter waves, which was recently realized by Anderson and Kasevich [S cience 781 (1998) 1686] with a condensate of Rb-87 atoms confined in an opt ical lattice. We solve the time-dependent Gross-Pitaevskii equation for thi s model by a novel fast algorithm and examine in detail the role of the ato mic interactions in determining the existence, the shape, the period of for mation and the size of the pulses. The transport behaviour of the system as a function of its governing parameters is summarized in a simple two-dimen sional diagram, (C) 1999 Published by Elsevier Science B.V. All rights rese rved.