Reduction of multipartite qubit density matrixes to bipartite qubit density matrixes and criteria of partial separability of multipartite qubit density matrixes

摘要

The partial separability of multipartite qubit density matrixes is strictlydefined. We give a reduction way from N-partite qubit density matrixes tobipartite qubit density matrixes, and prove a necessary condition that aN-partite qubit density matrix to be partially separable is its reduced densitymatrix to satisfy PPT condition.