Noise Correlations of Hard-core Bosons: Quantum Coherence and Symmetry   Breaking
  Noise correlations, such as those observable in the time of flight images of a released cloud, are calculated for hard-core bosonic (HCB) atoms. We find that the standard mapping of HCB systems onto spin-1/2 XY models fails in application to computation of noise correlations due to the contribution of multiply occupied virtual states in HCB systems. Such states do not exist in spin models. An interesting manifestation of such states is the breaking of particle-hole symmetry in HCB. We use noise correlations to explore quantum coherence of strongly correlated bosons in the fermionized regime with and without external parabolic confinement. Our analysis points to distinctive new experimental signatures of the Mott phase. 
Ana Maria Rey, Indubala I Satija and Charles W Clark