The quantum entanglement contained in density matrices

Yong Zhou

Published 2007-10-22, updated 2010-12-24Version 3

We point out that density matrices can only be used to describe quantum states, so the entanglement contained in a density matrix is just quantum entanglement. This means a bipartite state described by a density matrix contains quantum entanglement, unless the density matrix has the form $\rho_{AB}=\rho_A\otimes \rho_B$.