1. Department of Physics, National Tsing Hua University, 300044 Hsinchu, Taiwan
2. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, 300093, Taiwan
3. Department of Physics, National Changhua University of Education, Changhua 500, Taiwan
4. Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
5. Center for Quantum Technology, National Tsing Hua University, Hsinchu 300044, Taiwan