Stochastic dynamics of a trapped Bose-Einstein condensate

Abstract

We present a varional solution of the Langevin field equation describing the nonequilibrium dynamics of a harmonically trapped Bese-Einsten condensate. If the thermal cloud remains in equilibrium at all times, we find that the equation of motions for the parameters in our variational ansatz are equivalent to the Langevin equations describing the motion of a massive Brownain particle in an external potential. Moreover, these equations are coupled to a stochastic rate equation for the number of atoms in the condensate. As applications of our approach, we have calculated the collisional damping rates and frequencies of the low-lying collective excitations of a condensate with repulsive interactions, and have obtained a description of the growth and subsequent collapse of a condensate with the available experimental results in both cases.