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Separability Criterion for Density Matrices

Asher Peres

quant-pharXiv:quant-ph/9604005

Abstract

A quantum system consisting of two subsystems is separable if its density matrix can be written as ρ=ΣA wA\,ρA'ρA'', where ρA' and ρA'' are density matrices for the two subsytems. In this Letter, it is shown that a necessary condition for separability is that a matrix, obtained by partial transposition of ρ, has only non-negative eigenvalues. This criterion is stronger than Bell's inequality.

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