1. School of Instrumentation Science and Optoelectronics Engineering, Beihang University, Beijing, China
2. Key Laboratory of Ultra-Weak Magnetic Field Measurement Technology, Ministry of Education, School of Instrumentation and Optoelectronic Engineering, Beihang University, Beijing, China
3. National Institute of Metrology, Beijing, China
4. School of Automation, Beijing Institute of Technology(BIT), Beijing, China