  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.
