1. Center for Advanced Intelligence Project, RIKEN, 1-4-1 Nihombashi, Chuo-ku, Tokyo 103-0027, Japan
2. Advanced Technology Research Institute, KYOCERA, 3-7-1 minatomirai, Nishi-ku, Yokohama, Kanagawa 220-0012, Japan
3. Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8561, Japan
4. Center for Basic Research on Materials, National Institute for Materials Science, 1-2-1 Namiki, Tsukuba, Ibaraki 305-0047, Japan