Fractionalized Phase in an XY-Z_2 Gauge Model

We study a model with fractional quantum numbers using Monte Carlo techniques. The model is composed of bosons interacting though a $Z_2$ gauge field. We find that the system has three phases: a phase in which the bosons are confined, a fractionalized phase in which the bosons are deconfined, and a phase in which the bosons are condensed. The deconfined phase has a ``topological’’ order due to the degeneracy in the ground state of the gauge field. We discuss an experimental test proposed by Senthil and Fisher that uses the topological order to determine the existence of a deconfined, fractionalized phase.