Sr Optical Lattice Clock and Precision Optical Frequency Measurement at NIM

Two Sr optical lattice clocks are being built at the National Institute of Metrology of China (NIM). Sr1 was built on NIM's Hepingli Campus. It was first evaluated in 2015 and improved later on. In 2021, the systematic shift uncertainty of Sr1 was evaluated to be 2.9 × 10-17. Sr2 was started to be built on NIM's Changping Campus in 2017. The systematic shift uncertainty of Sr2 was evaluated to be 7.2 × 10-18 in 2022. With a new BBR optimizing process, the total BBR uncertainty of Sr2 is reduced to 4.6 × 10-18 which corresponds to the total uncertainty of Sr2 is evaluated to 6.5 × 10-18 in 2023. To compare these two Sr clocks, an optical frequency transfer fiber link with a length of 54 km was established between these two clocks. A preliminary study of generating a local time scale with Sr1 has been carried out at NIM. The time scale generated by post-processing of the comparison data between Sr1 and an H-maser demonstrated better stability than the time scale steered by UTC.