1. Institute for Quantum Optics and Center for Integrated Quantum Science and Technology (IQST) Ulm University, Albert Einstein Allee 11, Ulm 89081, Germany
2. State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
3. Research Center for Functional Materials, National Institute for Material Science, 1-1, Namiki, Tsukuba, Ibaraki 305-0044, Japan