Phys. Rev. A 60, 126–135 (1999)Optimal minimal measurements of mixed statesReceived 23 December 1998; published in the issue dated July 1999 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-average fidelity. We do this for up to three copies of the unknown state in a way that leads to the generalization to any number of copies, which we then present and prove. © 1999 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.60.126
DOI:
10.1103/PhysRevA.60.126
PACS:
03.67.-a
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