1. 1Department of Quantum Engineering and Systems Science, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 Japan
2. 2Central Research Institute of Electric Power Industry (CRIEPI), Iwadokita, 2-chome 11-1, Komae-shi, Tokyo 201 Japan
3. 3Japan Atomic Energy Research Institute (JAERI), Tokai-mura, Naka-gun, Ibaraki-ken 319-11 Japan