Experimental study of sub-Poissonian statistics in the transfer of momentum from light to atoms

We have studied the statistics of the absorption of photons by atoms by measuring the momentum distribution of an atomic beam that is deflected by a laser beam. We observe the transition from a Poissonian to a sub-Poissonian distribution, as we vary the detuning of the laser. The largest observed fractional deviation of the variance from Poissonian statistics is Q=-0.51±0.05, in agreement with theoretical predictions for our experimental conditions.