1. Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
2. Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan
3. Research Center for Integrated Quantum Electronics, Hokkaido University, Sapporo 060-8628, Japan
4. Systems Design Lab (d.lab), School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan