1. Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198,
Japan
2. Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
3. JST, PRESTO, 4-1-8 Honcho, Kawaguchi,
Saitama 332-0012, Japan
4. Angewandte Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany
5. Quantum-Phase Electronics Center, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
6. Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505,
Japan