1. Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.
2. Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, Netherlands.
3. RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.