1. National Laboratory of Solid State Microstructures and Research Institute of Superconductor Electronics, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
2. Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
3. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
4. School of Physics, Nanjing University, Nanjing 210093, China
5. Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA