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Analogy between optimal spin estimation and interferometry

Z. Hradil·M. Dusek
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Abstract

Scheme for optimal spin state estimation is considered in analogy with phase detection in interferometry. Recently reported coherent measurements yielding the average fidelity (N+1)/(N+2) for N particle system corresponds to the standard limit of phase resolution 1/\sqrt{N}. It provides the bound for incoherent measurements when each particle is detected separately and information is used optimally. For specific states, improvement up to the value 1/N is possible in quantum theory. The best results are obtained combining sequentially coherent measurements on fractional groups of particles.

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Z. Hradil, M. Dusek. 1999-11-16. Analogy between optimal spin estimation and interferometry. https://doi.org/10.1016/s0030-4018(00)00809-9

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