1. Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany
2. Physics Institute II, University of Cologne, Zülpicher Str. 77, 50937 Köln, Germany
3. Centre for Quantum Physics, Key laboratory of advanced optoelectronic quantum architecture and measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, China
4. Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
5. School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
6. Purdue Quantum Science and Engineering Institute, Purdue University, West Lafayette, Indiana 47907, USA
7. WPI-AIMR International Research Center for Materials Sciences, Tohoku University, Sendai 980-8577, Japan
8. Institute of Physics and Astronomy, Aarhus University, 8000 Aarhus-C, Denmark