1. Graduate School of Humanities and Sciences and Department of Physics, Faculty of Science, Ochanomizu University, Tokyo 112-8610
2. Advanced Research Laboratory, Hitachi, Ltd., 2520 Akanuma, Hatogaya, Saitama 350-0395
3. CREST, Japan Science and Technology Agency, 1-1-9 Yaesu, Chuo-ku, Tokyo 103-0028