Department of Mathematics, Capital Normal University, Beijing 100037, China;
Institute of Applied Mathematics, University of Bonn, 53115 Bonn, Germany;
Department of Mathematics, Capital Normal University, Beijing 100037, China;
Department of Mathematics, Capital Normal University, Beijing 100037, China;
Department of Mathematics, Capital Normal University, Beijing 100037, China;
Department of Mathematics, Capital Normal University, Beijing 100037, China;
separability; quantum entanglement;