Cavity-aided nondemolition measurements for atom counting and spin squeezing

摘要

Probing the collective spin state of an ensemble of atoms may provide a meansto reduce heating via the photon recoil associated with the measurement andprovide a robust, scalable route for preparing highly entangled states withspectroscopic sensitivity below the standard quantum limit for coherent spinstates. The collective probing relies on obtaining a very large optical depththat can be effectively increased by placing the ensemble within an opticalcavity such that the probe light passes many times through the ensemble. Herewe provide expressions for measurement resolution and spectroscopic enhancementin such cavity-aided non-demolition measurements as a function of cavitydetuning. In particular, fundamental limits on spectroscopic enhancements in$^{87}$Rb are considered.