Improved systematic evaluation of a strontium optical clock with uncertainty below $1\times 10^{-18}$
Zhi-Peng Jia, Jie Li, De-Quan Kong, Xiang Zhang, Hai-Wei Yu, Xiao-Yong Liu, Yu-Chen Zhang, Yuan-Bo Wang, Xian-Qing Zhu, Jia-Hao Zhang, Ming-Yi Zhu, Pei-Jun Feng, Xing-Yang Cui, Ping Xu, Xiao Jiang, Xiang-Pei Liu, Peng Liu, Han-Ning Dai, Yu-Ao Chen, Jian-Wei Pan
Published: 2025/9/17
Abstract
We report a systematic uncertainty of $9.2\times 10^{-19}$ for the USTC Sr1 optical lattice clock, achieving accuracy at the level required for the roadmap of the redefinition of the SI second. A finite-element model with {\it in situ}-validated, spatially-resolved chamber emissivity reduced blackbody radiation shift uncertainty to $6.3\times 10^{-19}$. Concurrently, an externally mounted lattice cavity combined with a larger beam waist suppressed density shifts. Enhanced lattice depth modulation consolidated lattice light shift uncertainty to $6.3\times 10^{-19}$ by enabling simultaneous determination of key polarizabilities and magic wavelength. Magnetic shifts were resolved below $10^{-18}$ via precision characterization of the second-order Zeeman coefficient. Supported by a crystalline-coated ultra-low-expansion cavity-stabilized laser and refined temperature control suppressing BBR fluctuations, the clock also achieves a frequency stability better than $1\times10^{-18}$ at 30,000-s averaging time. These developments collectively establish a new benchmark in USTC Sr1 clock performance and pave the way for high-accuracy applications in metrology and fundamental physics.