Product state
= Product state
{wiki}
A bipartite <density operator> is a product state when it factors as $\rho_A\otimes\rho_B$. A pure product state factors as $|\psi_A\rangle\otimes|\psi_B\rangle$; its <reduced density matrices> have rank one and zero <entanglement entropy>. Mixed product states can have nonzero marginal <Von Neumann entropy>.