  Atom interferometers using Bose-Einstein condensate that is confined in a
waveguide and manipulated by optical pulses have been limited by their short
coherence times. We present a theoretical model that offers a physically simple
explanation for the loss of contrast and propose the method for increasing the
fringe contrast by recombining the atoms at a different time. A simple,
quantitatively accurate, analytical expression for the optimized recombination
time is presented and used to place limits on the physical parameters for which
the contrast may be recovered.
