1. Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
2. Center for Atomic and Molecular Technologies, Osaka University, Suita, Osaka 565-0871, Japan
3. National Institute of Technology, Akashi College, Akashi, Hyogo 674-8501, Japan
4. Institute of Industrial Science, The University of Tokyo, Meguro, Tokyo 153-8505, Japan
5. Kawasaki Heavy Industries, Ltd., Akashi, Hyogo 673-8666, Japan