1. Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Mississippi 8171, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA
2. Graduate Institute of Applied Physics, National Taiwan University, Taipei 10617, Taiwan
3. Joint Quantum Institute, University of Maryland, College Park, Maryland 20742, USA
4. Department of Physics, National Taiwan University, Taipei 10617, Taiwan