1. Graduate Student, State Key Laboratory of Precision Measurement Technology and Instruments, Dept. of Precision Instrument, Tsinghua Univ., Beijing 100084, P.R. China.
2. Associate Professor, State Key Laboratory of Precision Measurement Technology and Instruments, Dept. of Precision Instrument, Tsinghua Univ., Beijing 100084, P.R. China (corresponding author).
3. Professor, State Key Laboratory of Precision Measurement Technology and Instruments, Dept. of Precision Instrument, Tsinghua Univ., Beijing 100084, P.R. China.
4. Associate Professor, State Key Laboratory of Precision Measurement Technology and Instruments, Dept. of Precision Instrument, Tsinghua Univ., Beijing 100084, P.R. China.