Quantum nonlocality and inseparability
Abstract
Description
A quantum system consisting of two subsystems is separable if its density matrix can be written as $ρ=\sum w_K ρ_K'\otimes ρ_K''$, where $ρ_K'$ and $ρ_K''$ are density matrices for the two subsytems, and the positive weights $w_K$ satisfy $\sum w_K=1$. A necessary condition for separability is derived and is shown to be more sensitive than Bell's inequality for detecting quantum inseparability. Moreover, collective tests of Bell's inequality (namely, tests that involve several composite systems simultaneously) may sometimes lead to a violation of Bell's inequality, even if the latter is satisfied when each composite system is tested separately.
14 pages LaTeX, to appear in proceedings of symposium on fundamental problems in quantum physics, Oviedo 1996 (Kluwer Academic Publishers). One figure may be requested from the author
14 pages LaTeX, to appear in proceedings of symposium on fundamental problems in quantum physics, Oviedo 1996 (Kluwer Academic Publishers). One figure may be requested from the author