Year: 2026
Type: preprint
Abstract: Redefining the International system of Units (SI) second requires independent frequency-ratio measurements between clocks based on different laboratories, with an overall uncertainty below 5E-18, to validate individual clock evaluations through consistency checks. Reaching this uncertainty over long distances has remained challenging. So far, comparisons at this level have been achieved only a few times, between co-located clocks, and their results disagree markedly. Previous high-precision comparisons have therefore been limited to local or kilometre-scale links. Here we compare a ytterbium optical lattice clock in Wuhan with a strontium optical lattice clock in Shanghai over a phase-stabilized fiber link spanning 1350 km, and determine the Yb/Sr frequency ratio to be 1.207 507 039 343 337 716 0(26), with a Bayesian statistical uncertainty of 1.14E-18 and a total uncertainty of 2.18E-18. To our knowledge, this is the first intercity long distance frequency-ratio measurement, whose total uncertainty reaches the level required by the redefinition roadmap. The measured ratio exhibits a significant correlation with Earth tides and its response agree with the model within the statistical uncertainty. At intercity scale, this comparison demonstrates the capability of an optical-clock network for frequency comparison and Earths gravitational-potential sensing, a key step toward a wide-area optical-clock network.
Source: arXiv (Cornell University)
Authors: Hou, Lei, Liu, Xiang-Pei, Xiong, Zhuan-Xian, Chen, Fa-Xi, Song, Wen-Xuan, Guan, Jian-Yu, Zhu, Qiang, Zhang, Yu-Chen, Zhang, Xiang, Wang, Bing, Xiong, De-Zhi, Kong, De-Quan, Zhang, Jia-Hao, Liao, Long-Fei, Wang, Shao-Mao, Cui, Xing-Yang, Xu, Ping, Liu, Peng, Li, Jie, Jiang, Xiao, He, Ling-Xiang, Li, Li-Bo, Shen, Qi, Xie, Youchao, Wang, Lei, Liao, Sheng-Kai, Yin, Juan, Peng, Cheng-Zhi, Shen, Wen-Bin, Lu, Bao-Long, Dai, Han-Ning, Chen, Yu-Ao, Zhang, Qiang, Jiang, Hai-Feng, Pan, Jian-Wei
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223820958