1. Quantum-Phase Electronics Center and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan.
2. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
3. Department of Physics, Faculty of Science, Beirut Arab University, Beirut 11-5020, Lebanon.
4. National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan.
5. Department of Physics, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
6. Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan.
7. Department of Physics, Graduate School of Science, Tohoku University, 6-3, Aramaki Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan.