1. Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
2. Research Center for Emerging Computing Technologies, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Tsukuba, Ibaraki 305-8568, Japan
3. NTT Communication Science Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198, Japan
4. Center for Quantum Information and Quantum Biology, Osaka University, Toyonaka, Osaka 560-0043, Japan