Physics: New nuclear clocks on the block (Nature)

The first working nuclear clocks based on isotopes of thorium-229 are presented in two papers published in Nature this week. The clocks, which keep time by monitoring how light interacts with an atomic nucleus, may have the potential to outperform atomic clocks. Such accurate timekeeping could facilitate research to probe fundamental physics.

For more than 70 years atomic clocks have been used to measure time precisely. Atomic clocks measure time by tracking transitions of electrons as they switch back and forth between two energy states. In 2003 it was proposed that tracking transitions in the atomic nuclei might reach even higher levels of accuracy, as nuclei are much smaller than atoms (the nucleus, located at the atom’s core, makes up only a small fraction of the atom’s volume). A radioactive isotope of the metal thorium, thorium-229, was proposed as an ideal nucleus as its low energy state could allow lasers to track the frequency of the transitions.

In two separate papers, Thorsten Schumm and colleagues and Shiqian Ding and colleagues report the realization of the first working nuclear clocks based on isotopes of thorium-229. Both groups embed thorium-229 in a calcium fluoride crystal and measure the transition frequency, or the ‘tick’ of the clock. Although both clocks held time with very little drift, their current stability is below that of the best atomic clocks. Schumm and colleagues note that further work could increase the stability by around four orders of magnitude. However, they demonstrate that their clock can carry out a precision physics experiment, detecting dark matter at a level that competes with the best atomic clocks.

Together, these findings demonstrate the future potential of the nuclear clock to provide accurate timekeeping and a tool to probe fundamental physics.

• Article
• Open access
• Published: 07 October 2026

Toscani De Col, L., Riebner, T., Morawetz, I. et al. A thorium-229 optical nuclear clock with feedback loop. Nature (2026). https://doi.org/10.1038/s41586-026-11084-4

• Article
• Open access
• Published: 07 October 2026

Huang, B., Yan, G., Xiao, Q. et al. A nuclear clock synchronized to ²²⁹Th. Nature (2026). https://doi.org/10.1038/s41586-026-11122-1

News & Views: Nuclear clocks tick for the first time
https://www.nature.com/articles/d41586-026-03060-9

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