First Evaluation and Frequency Measurement of the Strontium Optical Lattice Clock at NIM

An optical lattice clock based on 87Sr is built at National Institute of Metrology (NIM) of China. The systematic frequency shifts of the clock are evaluated with a total uncertainty of 2.3×10−16. To measure its absolute frequency with respect to NIM's cesium fountain clock NIM5, the frequency of a flywheel H-maser of NIM5 is transferred to the Sr laboratory through a 50-km-long fiber. A fiber optical frequency comb, phase-locked to the reference frequency of this H-maser, is used for the optical frequency measurement. The absolute frequency of this Sr clock is measured to be 429228004229873.7(1.4)Hz.