Facial Structures for Separable States
by Hyun-Suk Choi and Seung-Hyeok Kye
J. Korean Math. Soc. 49 (2012), 623-639.
The convex cone $\mathbb V_1$ generated by separable states is contained in the cone $\mathbb T$ of all positive semi-definite block matrices whose block transposes are also positive semi-definite. We characterize faces of the cone $\mathbb V_1$ induced by faces of the cone $\mathbb T$ which are determined by pairs of subspaces of matrices.