A nuclear clock synchronized to 229Th

Abstract Atomic clocks have made time and frequency the most precisely measured quantities in physics, progressing from microwave standards that realize the SI second 1 to optical clocks with unprecedented precision 2 . A nuclear clock transfers the frequency reference from an electronic to a nuclear transition and the uniquely low-lying, laser-accessible, isomeric transition in 229 Th currently offers the most practical route to compact, robust timekeeping and sensitive tests of fundamental physics 3–8 . Realizing such a clock requires turning spectroscopy of the 229 Th nuclear resonance 9–17 into a stable discriminator for steering a traceable oscillator. Here we demonstrate a 229 Th nuclear clock by stabilizing a continuous-wave, narrow-linewidth 148.4 nm vacuum-ultraviolet (VUV) laser 18 to a resolved, weakly temperature-sensitive nuclear transition 17,19 in 229 Th:CaF 2 crystals 20–22 . A 10-μW VUV source generated by four-wave mixing in cadmium vapour 18,23,24 and phototube-based frequency modulation absorption readout provide a fast, high-signal-to-noise nuclear discriminator. The clock reaches a fractional frequency instability of $$5\times 1{0}^{-13}/\sqrt{\tau /{\rm{s}}}$$ 5 × 1 0 − 13 / τ / s for averaging time τ . Clock-transition frequencies measured in two independently fabricated crystals agree at the 10 −13 level and are consistent with previous VUV-comb measurements on other 229 Th:CaF 2 crystals 17 . These results establish laser-addressed nuclei as operational clock references and provide a reproducible solid-state platform for compact nuclear clocks, nuclear quantum sensors and precision tests of fundamental physics.

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Publication Details

Journal
Nature
Published
2026-10-07
DOI
https://doi.org/10.1038/s41586-026-11122-1
Citations
1
Primary Topic
Advanced Frequency and Time Standards
Type
article
Field-Weighted Citation Impact
2.86
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article

A nuclear clock synchronized to 229Th

Yuxiang Mo, Dapeng Jiang, Youyong Li, Chao Yan et al.
1 citations
Nature
Advanced Frequency and Time Standards
2.86
article

A nuclear clock synchronized to 229Th

Yuxiang Mo, Dapeng Jiang, Youyong Li, Chao Yan, Qiaorui Gong, Gleb Penyazkov, 李玉香, Liangbi Su, Lingfeng Yan, Bing-Kun Lu, Taoxiang Sun, Shining N. Zhu, Shiqian Ding, Xiangliang Li, Hang Yin, Jun Lin, Beichen Huang, Zhi-Ang Chen, Ningyuan Ma, Xuegang Liu, Xiaobo Qian, Yanzhang Wu, Yuefei Wang, Qi Xiao, Haoyu Shi, Zhenhai Zhan, Juxian Li, Wenhao Bu, Gaowei Yan, Xibo Zhang, Longsheng Ma, Lin Li, Yige Lin, Chengchun Zhao, Zhen Zhang, Haochen Tian, Qiange He, Peixiong Zhang, Shanming Li
article en
1 citations

Abstract

Abstract Atomic clocks have made time and frequency the most precisely measured quantities in physics, progressing from microwave standards that realize the SI second 1 to optical clocks with unprecedented precision 2 . A nuclear clock transfers the frequency reference from an electronic to a nuclear transition and the uniquely low-lying, laser-accessible, isomeric transition in 229 Th currently offers the most practical route to compact, robust timekeeping and sensitive tests of fundamental physics 3–8 . Realizing such a clock requires turning spectroscopy of the 229 Th nuclear resonance 9–17 into a stable discriminator for steering a traceable oscillator. Here we demonstrate a 229 Th nuclear clock by stabilizing a continuous-wave, narrow-linewidth 148.4 nm vacuum-ultraviolet (VUV) laser 18 to a resolved, weakly temperature-sensitive nuclear transition 17,19 in 229 Th:CaF 2 crystals 20–22 . A 10-μW VUV source generated by four-wave mixing in cadmium vapour 18,23,24 and phototube-based frequency modulation absorption readout provide a fast, high-signal-to-noise nuclear discriminator. The clock reaches a fractional frequency instability of $$5\times 1{0}^{-13}/\sqrt{\tau /{\rm{s}}}$$ 5 × 1 0 − 13 / τ / s for averaging time τ . Clock-transition frequencies measured in two independently fabricated crystals agree at the 10 −13 level and are consistent with previous VUV-comb measurements on other 229 Th:CaF 2 crystals 17 . These results establish laser-addressed nuclei as operational clock references and provide a reproducible solid-state platform for compact nuclear clocks, nuclear quantum sensors and precision tests of fundamental physics.

Nature
Chinese Academy of Sciences (CN), Peking University (CN), Shanghai Institute of Applied Physics (CN), Shanghai Institute of Optics and Fine Mechanics (CN), Collaborative Innovation Center of Advanced Microstructures (CN), Beijing Academy of Quantum Information Sciences (CN), National Institute of Metrology (CN), Shanghai Institute of Ceramics (CN), University of Chinese Academy of Sciences (CN), State Key Laboratory of Low-Dimensional Quantum Physics, National Laboratory of Solid State Microstructures, Frontier Science Center for Quantum Information of the Ministry of Education of China (CN), East China Normal University (CN), Nanjing University (CN), Tsinghua University (CN)
Openalex Percentile: Top 7%
Advanced Frequency and Time Standards
2.86
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