1. School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
2. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
3. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
4. Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
5. Istituto di Fotonica e Nanotecnologie (IFN), CNR, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy