1. Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
2. Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
3. Department of Physical Sciences, Aoyama Gakuin University, Sagamihara, Kanagawa 252-5258, Japan
4. CSAIL, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A.
5. Trans-scale Quantum Science Institute, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan