BEC is like laser, with perfect coherence: from an experimental point of view

In this work, BEC has been shown possessing the same kind of coherence properties of laser, as expected. The researchers measure directly the third order correlation functions regarding atom bunching (for bosons), g(0,t1,t2), which shows the likelihood of having three particles detected at moments 0, t1 and t2, respectively. For thermal bosons, this function features a broad peak, while for BEC it is rather uniform. This was just observed [Science, 331:3046(2011)] !

A major advance in understanding the behavior of light was to describe the coherence of a light source by using correlation functions that define the spatio-temporal relationship between pairs and larger groups of photons. Correlations are also a fundamental property of matter. We performed simultaneous measurement of the second- and third-order correlation functions for atoms. Atom bunching in the arrival time for pairs and triplets of thermal atoms just above the Bose-Einstein condensation (BEC) temperature was observed. At lower temperatures, we demonstrated conclusively the long-range coherence of the BEC for correlation functions to third order, which supports the prediction that like coherent light, a BEC possesses long-range coherence to all orders.