1. Department of Physics, University of Science and Technology Beijing, Beijing 100083, People's Republic of China
2. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, People's Republic of China
3. College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Science, Beijing 100049, People's Republic of China
4. Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Science, Beijing 100049, People's Republic of China