Multiparticle covariance matrices and the impossibility of detecting graph state entanglement with two-particle correlations
arXiv:1006.1594 · doi:10.1103/PhysRevA.82.032306
Abstract
We present a criterion for multiparticle entanglement based on covariance matrices. On the one hand, the criterion allows to detect bound entangled states which are not detected by other criteria; on the other hand, some strongly entangled pure states such as the GHZ states are not detected. We show, however, that this is a general phenomenon: No separability criterion based on two-particle correlations can recognize the entanglement in the family of graph states, to which the GHZ states belong.
10 pages, 3 figures
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