Yb/Sr optical clock comparison at 2.2E-18 uncertainty over a 1350-km fiber link
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Lei Hou, Xiang-Pei Liu, Zhuan-Xian Xiong, Fa-Xi Chen, Wen-Xuan Song, Jian-Yu Guan et al. · arXiv: 2610.34250v1 · Summary page
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Distant clocks become a probe of gravity
An optical clock comparison has connected Wuhan and Shanghai through a phase-stabilized fiber link spanning 1350 km. Comparing ytterbium and strontium clocks, the researchers report a total uncertainty of 2.18E-18—below the target set by the roadmap toward redefining the second. Such comparisons test whether clocks built around different atoms and operated in different laboratories tell a consistent story, rather than merely agreeing under shared local conditions.
The comparison also picked up a signal correlated with Earth tides, with a response consistent with the model within statistical uncertainty. Gravity changes the rate at which clocks tick, so a connection built to improve timekeeping can also sense differences in gravitational potential. This preprint brings the requirements of international metrology and the possibilities of clock-based geophysical sensing into the same long-distance experiment.
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