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Optimal minimal measurements of mixed states

G. Vidal·J. I. Latorre·P. Pascual·R. Tarrach
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Abstract

The optimal and minimal measuring strategy is obtained for a two-state system prepared in a mixed state with a probability given by any isotropic a priori distribution. We explicitly construct the specific optimal and minimal generalized measurements, which turn out to be independent of the a priori probability distribution, obtaining the best guesses for the unknown state as well as a closed expression for the maximal mean averaged fidelity. We do this for up to three copies of the unknown state in a way which leads to the generalization to any number of copies, which we then present and prove.

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G. Vidal, J. I. Latorre, P. Pascual, R. Tarrach. 1998-12-24. Optimal minimal measurements of mixed states. https://doi.org/10.1103/physreva.60.126

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