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We investigate the quantum-mechanical noise in spectroscopic experiments on ensembles of N two-level (or spin-1/2) systems where transitions are detected by measuring changes in state population. By preparing correlated states, here called squeezed spin states, we can increase the signal-to-noise ratio in spectroscopy (by approximately N^1/2 in certain cases) over that found in experiments using uncorrelated states. Possible experimental demonstrations of this enhancement are discussed.
Wineland et al. (1992) studied this question.