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.