1996/08/19 by Asher Peres · 180 citations
Computer Science · Physics and Astronomy · #Quantum Information and Cryptography #Quantum Mechanics and Applications #Quantum Computing Algorithms and Architecture
paper · doi:10.1103/physrevlett.77.1413
A quantum system consisting of two subsystems is separable if its density matrix can be written as \ensuremathρ\phantom\rule0ex0ex=\phantom\rule0ex0ex\ensuremathΣAwA\ensuremathρA^\ensuremath'\ensuremath\bigotimes\ensuremathρA^\ensuremath'\ensuremath', where \ensuremathρA^\ensuremath' and \ensuremathρA^\ensuremath'\ensuremath' are density matrices for the two subsystems, and the positive weights wA satisfy \ensuremathΣwA\phantom\rule0ex0ex=\phantom\rule0ex0ex1. In this Letter, it is proved that a necessary condition for separability is that a matrix, obtained by partial transposition of \ensuremathρ, has only non-negative eigenvalues. Some examples show that this criterion is more sensitive than Bell's inequality for detecting quantum inseparability.