1. Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany
2. Institute of Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
3. Physics Institute II, University of Cologne, Zülpicher Strasse 77, 50937 Köln, Germany
4. Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Ministry of Education, School of Physics, Beijing Institute of Technology, Beijing 100081, China