1. Graduate School of Pure & Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Japan
2. Division of Materials Science, Faculty of Pure & Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan
3. Superconducting Spectronics Group, Nanoelectronics Research Institute, AIST, Central 2, 1-1-1, Umezono, Tsukuba, Ibaraki 305-8568, Japan
4. QuTech, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
5. Department of Physics, University of Central Florida, 4111 Libra Drive, Orlando, Florida 32816-2385, USA