1 Department of Automation, Tsinghua University, Beijing 100084, China
2 Institute for Brain and Cognitive Science, Tsinghua University, Beijing 100084, China
3 Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
4 Beijing Innovation Center for Future Chip, Tsinghua University, Beijing 100084, China
5 Institute of Microelectronics, Tsinghua University, Beijing 100084, China
6 Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing 100084, China
7 e-mail: lin-x@tsinghua.edu.cn
8 e-mail: qhdai@tsinghua.edu.cn