Dynamics of a Bose-Einstein-condensate bright soliton in an expulsive potential

We theoretically investigate the dynamics of a matter-wave soliton created in a harmonic potential, which is attractive in the transverse direction but expulsive in the longitudinal direction. This Bose-Einstein-condensate (BEC) bright soliton made of 7Li atoms has been observed in a recent experiment [ Khaykovich et al. Science 296 1290 (2002)]. We show that the nonpolynomial Schrödinger equation, an effective one-dimensional equation we derived from the three-dimensional Gross-Pitaevskii equation, is able to reproduce the main experimental features of this BEC soliton in an expulsive potential.