Yb/Sr optical clock comparison at 2.2E-18 uncertainty over a 1350-km fiber link
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.
Related
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- Optical Signals Synthesized from an Optical Lattice Clock with Uncertainty of 1.3E-17
- Improved systematic uncertainty evaluation of the 171Yb optical lattice clock NMIJ-Yb1 with uncertainty of 2.6×10−17
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- International atomic clock comparison achieving 5× 10−18 uncertainty
BibTeX
@misc{hou2026ybsr,
title = {{Yb/Sr optical clock comparison at 2.2E-18 uncertainty over a 1350-km fiber link}},
author = {Lei Hou and Xiang-Pei Liu and Zhuan-Xian Xiong and Fa-Xi Chen and Wen-Xuan Song and Jian-Yu Guan and Qiang Zhu and Yu-Chen Zhang and Xiang Zhang and Bing Wang and De-Zhi Xiong and De-Quan Kong and Jia-Hao Zhang and Long-Fei Liao and Shao-Mao Wang and Xing-Yang Cui and Ping Xu and Peng Liu and Jie Li and Xiao Jiang and Ling-Xiang He and Li-Bo Li and Qi Shen and Youchao Xie and Lei Wang and Sheng-Kai Liao and Juan Yin and Cheng-Zhi Peng and Wen-Bin Shen and Bao-Long Lu and Han-Ning Dai and Yu-Ao Chen and Qiang Zhang and Hai-Feng Jiang and Jian-Wei Pan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.34250},
eprint = {2610.34250},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.34250},
}
RIS
TY - UNPB
TI - Yb/Sr optical clock comparison at 2.2E-18 uncertainty over a 1350-km fiber link
AU - Lei Hou
AU - Xiang-Pei Liu
AU - Zhuan-Xian Xiong
AU - Fa-Xi Chen
AU - Wen-Xuan Song
AU - Jian-Yu Guan
AU - Qiang Zhu
AU - Yu-Chen Zhang
AU - Xiang Zhang
AU - Bing Wang
AU - De-Zhi Xiong
AU - De-Quan Kong
AU - Jia-Hao Zhang
AU - Long-Fei Liao
AU - Shao-Mao Wang
AU - Xing-Yang Cui
AU - Ping Xu
AU - Peng Liu
AU - Jie Li
AU - Xiao Jiang
AU - Ling-Xiang He
AU - Li-Bo Li
AU - Qi Shen
AU - Youchao Xie
AU - Lei Wang
AU - Sheng-Kai Liao
AU - Juan Yin
AU - Cheng-Zhi Peng
AU - Wen-Bin Shen
AU - Bao-Long Lu
AU - Han-Ning Dai
AU - Yu-Ao Chen
AU - Qiang Zhang
AU - Hai-Feng Jiang
AU - Jian-Wei Pan
PY - 2026
DA - 2026/10/25
PB - arXiv
DO - 10.48550/arxiv.2610.34250
UR - https://arxiv.org/abs/2610.34250
AB - 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.
ER -