1. Nanoscale Quantum Photonics Laboratory, RIKEN, Saitama 351-0198, Japan
2. Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics, Saitama 351-0198, Japan
3. Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
4. Department of Electrical Engineering, The University of Tokyo, Tokyo 113-8656, Japan