Quantum nondemolition measurements using a crossed Kerr effect between atomic and light fields.

Abstract

We analyze the coupling between the fluctuations of an atomic beam incident on an evanescent wave mirror and the fluctuations of the laser beam producing the evanescent potential barrier. We show that this coupling is equivalent to a crossed Kerr effect between an atomic field and a light field, and that the consistency of the theory requires that both fields be subject to symmetrical commutation relations and quantum fluctuations. We show in particular that the phase shift undergone by the light field during the atomic reflection process permits a quantum nondemolition measurement of the incident atomic intensity.