1. State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Electronics Engineering and Computer Science, and Center for Quantum Information Technology, Peking University, Beijing 100871, China
2. Department of Physics, University of California, Berkeley, California 94720-7300, USA
3. St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia
4. Institute of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Kraków, Poland
5. Johannes Gutenberg-University Mainz, 55128 Mainz, Germany
6. Helmholtz Institute Mainz, 55099 Mainz, Germany
7. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA