1. Institute of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China
2. State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Electronics, and Center for Quantum Information Technology, Peking University, Beijing 100871, China
3. College of Liberal Arts and Sciences, and Interdisciplinary Center for Quantum Information, National University of Defense Technology, Changsha 410073, China