1. College of Engineering and Applied Sciences, and National Laboratory of Solid State Microstructures Nanjing University Nanjing 210023 China
2. Key Laboratory of Quantum Information University of Science and Technology of China Hefei Anhui 230026 China
3. School of Physics Nanjing University Nanjing 210023 China
4. Department of Physics University of Arkansas Fayetteville AR 72701 USA
5. Jiangsu Key Laboratory of Artificial Functional Materials Nanjing University Nanjing 210093 China