1. School of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, P. R. China
2. Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu 611731, P. R. China
3. Big Data Research Center, University of Electronic Science and Technology of China, Chengdu 611731, P. R. China
4. Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland