1. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, College of Physics and Electronics Engineering, Shanxi University, Taiyuan 030006, China
2. State Key Laboratory for Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
3. Department of Physics, St. Petersburg State University, Ulyanovskaya Street 1, Petrodvoretz, St. Petersburg 198504, Russia