The Hanbury Brown Twiss Effect for Atoms

We have observed two-particle correlations in a cloud of metastable helium atoms released from a magnetic trap. We use a microchannel plate detector to achieve single atom detection. For clouds above the Bose-Einstein condensation transition temperature, we observe the Hanbury Brown Twiss effect, an enhanced pair detection probability for separations smaller than the atomic coherence length. Below the BEC transition the enhancement vanishes. We observe the effect in three-dimensions and study its variation with the cloud size.