  Coherence properties of Bose-Einstein condensates offer the potential for
improved interferometric phase contrast. However, decoherence effects due to
the mean-field interaction shorten the coherence time, thus limiting potential
sensitivity. In this work, we demonstrate increased coherence times with number
squeezed states in an optical lattice using the decay of Bloch oscillations to
probe the coherence time. We extend coherence times by a factor of 2 over those
expected with coherent state BEC interferometry. We observe quantitative
agreement with theory both for the degree of initial number squeezing as well
as for prolonged coherence times.
