QUANTUM-NONDEMOLITION MEASUREMENTS USING A CROSSED KERR-EFFECT BETWEEN ATOMIC AND LIGHT FIELDS

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