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Structural physical approximations of unphysical maps and generalized quantum measurements

Jaromir Fiurasek
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Abstract

We investigate properties of the structural physical approximation (SPA) of the partial transposition map recently introduced by Horodecki and Ekert [quant-ph/0111064]. We focus on the case of two-qubit states and show that in this case the map has the structure of a generalized quantum measurement followed by preparation of a suitable output state. We also introduce SPA for map that transforms two copies of density matrix of a single qubit onto a square of that matrix. We prove that also this map is essentially a generalized quantum measurement.

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Jaromir Fiurasek. 2001-11-20. Structural physical approximations of unphysical maps and generalized quantum measurements. https://doi.org/10.1103/physreva.66.052315

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