1. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan
2. Department of Advanced Materials Science, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan
3. National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
4. Institute of Engineering Innovation, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
5. PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan
6. Department of Quantum Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan