1. State Key Laboratory of Superlattices and MicrostructuresInstitute of SemiconductorsChinese Academy of Sciences Beijing 100083 P. R. China
2. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
3. State Key Laboratory of Superlattices and MicrostructuresInstitute of SemiconductorsChinese Academy of Sciences Beijing 100083 China
4. School of Physics and AstronomyUniversity of Nottingham Nottingham NG7 2RD UK
5. Center for Excellence in Topological Quantum ComputationUniversity of Chinese Academy of Science Beijing 100049 P. R. China