Phys. Rev. Lett. 77, 1413–1415 (1996)Separability Criterion for Density MatricesReceived 8 April 1996; published in the issue dated 19 August 1996 A quantum system consisting of two subsystems is separable if its density matrix can be written as ρ = ΣAwAρA′⊗ρA′′, where ρA′ and ρA′′ are density matrices for the two subsystems, and the positive weights wA satisfy ΣwA = 1. In this Letter, it is proved that a necessary condition for separability is that a matrix, obtained by partial transposition of ρ, has only non-negative eigenvalues. Some examples show that this criterion is more sensitive than Bell's inequality for detecting quantum inseparability. © 1996 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.77.1413
DOI:
10.1103/PhysRevLett.77.1413
PACS:
03.65.Bz, 03.65.Ca
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