Quantum nondemolition measurements of photon number by atomic beam deflection

We present a new quantum nondemolition measurement scheme in which a measure of the photon statistics of a cavity field can be achieved by monitoring the deflection of atoms interacting with the field. Repeated measurements result in the collapse of the photon distribution in the field to a number state. Quantum jumps in the photon number are observed when the cavity field is coupled to an external reservoir.