1. School of Integrated Circuit Science and Engineering, Beijing Advanced Innovation Center for Big Data and Brain Computing, Beihang University, Beijing 100191, China
2. Hefei Innovation Research Institute, Beihang University, Hefei 230013, China
3. Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
4. Department of Physics, Beihang University, Beijing 100191, China
5. Department of Physics, Technical University of Munich, Garching 85748, Germany