1. School of Physics, Beijing Institute of Technology, Beijing 100081, P. R. China
2. Center for Condensed Matter Sciences and Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 106, Taiwan, ROC
3. Institute of Physics, EIT 2, Faculty of Electrical Engineering and Information Technology, University of the Bundeswehr Munich, Neubiberg 85577, Germany
4. Department of Physics, College of Science, Sultan Qaboos University, AL Khoud, Muscat 123, Oman
5. Quantum Information Center, Chung Yuan Christian University, Taoyuan 32023, Taiwan, ROC
6. Department of Physics, National Taiwan University, Taipei 106, Taiwan, ROC