1. Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
2. Division of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan
3. Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
4. Institute for Quantum Optics and Center for Integrated Quantum Science and Technology, Ulm University, Ulm D-89081, Germany
5. Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816-2385, USA