[1] Univ Tokyo, Grad Sch Engn, Dept Elect Engn, Bunkyo Ku, Tokyo 1138656, Japan
[2] Univ Tokyo, Cryogen Ctr, Bunkyo Ku, Tokyo 1130032, Japan
[3] Electrotech Lab, Tsukuba, Ibaraki 3058568, Japan
[4] Japan Sci & Technol Corp, CREST, Kawaguchi 3320012, Japan