Quantum-nondemolition measurements using cold trapped atoms: Comparison between theory and experiment

In this paper we present a detailed theoretical analysis of a recent quantum-nondemolition experiment in optics using cold atoms in a magneto-optical trap as a nonlinear medium. A signal beam and a meter beam from two independent lasers are coupled within a h-type three-level scheme in the D1 line of Rb-87 atoms. The experimental results for the relevant quantum correlations of the fields, that represent up to now the best achievements for a single back-action evading measurement, are found in a remarkably good agreement with the theoretical predictions from a fully quantum model for three-level atoms in a doubly resonant cavity.