1. State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Weijin Road 92, Nankai District, CN-300072 Tianjin, China
2. Nanchang Institute for Microtechnology of Tianjin University, Weijin Road 92, Nankai District, 300072 Tianjin, China
3. Institute of Experimental Physics, Johannes Kepler University Linz, A-4040 Linz, Austria