Cyril Vaneph, Tommaso Tufarelli, Marco G. Genoni
We study the estimation of a two-phase rotation in a finite dimensional spin system. We consider two-mode spin squeezed probe states and discuss the role of two-mode spin squeezing in this kind of estimation. After deriving the ultimate bounds posed by quantum mechanics for such probe states, we present a measurement scheme able to exploit two-mode spin squeezing in order to improve the measurement sensitivity. We discuss the case where, even in the presence of two-mode spin squeezing, the coherent state strategy yields a better performance and thus the standard quantum limit is not overcome. Then, by considering optimized two-mode squeezed probe states, we show that our measurement scheme always beats the standard quantum limit, and approaches the ultimate bounds for large values of the spin dimension.
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http://arxiv.org/abs/1211.7224
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