1. Department of Physics Tsinghua University Beijing 100084 P. R. China
2. State Key Laboratory of Low‐Dimensional Quantum Physics Tsinghua University Beijing 100084 P. R. China
3. School of Physics, State Key Laboratory of Crystal Materials Shandong University Jinan 250100 P. R. China
4. Frontier Science Center for Quantum Information Beijing P. R. China
5. Beijing National Research Center for Information Science and Technology Beijing P. R. China
6. Beijing Academy of Quantum Information Sciences Beijing P. R. China