Atom loss from the ${}^{85}$Rb Bose-Einstein condensate by a Feshbach resonance

Loss of atoms from a ${}^{85}$Rb condensate on passage through a Feshbach resonance is analyzed using the generalized parametric approximation that takes into account quantum many-body effects. These effects lead to a substantial increase of the losses. A better agreement with experiments is achieved, compared to predictions of mean-field theories. The method provides much insight into the quantum effects involved, and on the nature of entangled atom pairs produced by the loss.