1. Department of Physics and Electronics, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
2. Institute for Nanofabrication Research, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
3. Materials and Life Science Division, J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
4. National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
5. Department of Quantum Engineering, Nagoya University, Nagoya, Aichi 464-8603, Japan