1State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 2Key Laboratory of Atomic Frequency Standards, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 3University of Chinese Academy of Sciences, Beijing 100049
Abstract：Frequency comparison is one of the most efficient ways to evaluate the performance of a frequency standard. Based on the pre-existing 40Ca+ optical frequency standard, we set up the second 40Ca+ optical frequency standard, which has been improved in the materials and structure of ion traps for better control of the magnetic field. After the compensation, the residual magnetic field at the position of the ion is adjusted to be ～500 nT with a long time jitter of ～10 nT, which is better than the pre-existing 40Ca+ optical frequency standard. We realize the '4-point-closed-loop locking' on the second 40Ca+ optical frequency standard after a series of preparatory works. Through half an hour of measurement time, the two frequency standards exhibited a stability of 2.1×10?13τ?1/2 and a relative frequency difference of 1.5 (2.9) Hz.
2014, Vol. 31 
