Decoherence due to three-body loss and its effect on the state of a Bose-Einstein condensate.

A Born-Markov master equation is used to investigate the decoherence of the state of a macroscopically occupied mode of a cold atom trap due to three-body loss. In the large-number limit only coherent states remain pure for times longer than the decoherence time: the time it takes for just three atoms to be lost from the trap. For large numbers of atoms (N>10(4)) the decoherence time is found to be much faster than the phase-collapse time caused by intratrap atomic collisions.