1. Dipartimento Interateneo di Fisica, Università degli Studi di Bari and Politecnico di Bari, CNR-IFN BARI, via Amendola 173, Bari, Italy
2. Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA
3. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China