1. Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
3. Department of Physics, National Taiwan University, Taipei 10617, Taiwan
4. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
5. Frontier Research Center on Fundamental and Applied Science of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan