Abstract

In a Bose-Einstein condensate due to the very low temperature the s-wave scattering length can be used as a measure for the strength of the atomatom interaction. Under typical experimental conditions this interaction is weak and, hence, can be treated in terms of a mean field. However, when the scattering length is large or the density is high, the mean field approximation breaks down. In this collisional (hydrodynamic) regime, effects of the interactions such as quantum depletion¹ or shifts in the frequencies of the elementary excitations² become large. It is therefore of great interest to study condensates close to or in the collisional regime. It has been demonstrated in recent experiments that the scattering length and thus the interactions among the atoms can be tuned by means of a Feshbach resonance.^3-6 In the vicinity of Feshbach resonances, however, the increase of the cross-section for elastic collisions is accompanied by a dramatic increase of particle losses.^7,8

© 2001 Optical Society of America