The atomic Hanbury Brown and Twiss expriment: 
fluctuations in cold quantum gases
 Chris Westbrook, 
Institut d’Optique Theorique et Appliquee, Orsay, France

In one of his famous papers describing the statistics of Bosons in 1924,

Einstein pointed out number fluctuations in a Bose gas should be much

greater than in one governed by Maxwell-Boltzmann statistics. He also

recognized an interference effect was at the origin of the fluctuations. In

the 1950's Hanbury Brown and Twiss performed a very clear experimental

demonstration when they discovered the bunching of photons from a thermal

source of light, but the experiment raised many questions. What was actually

quantum mechanically interfering? The many fascinating theoretical

discussions of photon bunching include the Nobel prize winning work of R.

Glauber. I will discuss recent experiments to study the analogous effect

with ultra-cold atoms. In addition to showing the atom optical analog of the

Hanbury Brown and Twiss effect, it is possible to create and observe

situations unknown in optics, where interactions between particles play an

important role.