A thorium-229 optical nuclear clock with feedback loop

Abstract The laser-accessible nuclear transition in the thorium-229 isotope has been identified as a candidate for realizing an optical nuclear clock 1 that might outperform current optical clocks based on electron-shell transitions in atoms or ions 2 . It is expected to be more robust against external perturbations 3,4 and to provide enhanced sensitivity in clock-based tests of the fundamental principles of physics 5,6 . Here we realize a thorium-229 nuclear clock by stabilizing a continuous-wave laser to the 148-nm nuclear transition with rapid feedback based on absorption spectroscopy 7 . The thorium-229 nuclei are embedded in a millimetre-sized, room-temperature calcium fluoride crystal. A subharmonic of the 148-nm radiation is continuously compared with a Yb + single-ion clock. The nuclear clock shows a shot-noise-limited fractional frequency instability of $$3\times 1{0}^{-12}/\sqrt{\tau /{\rm{s}}}$$ 3 × 1 0 − 12 / τ / s where τ is the averaging time, approaching 10 −15 instabilities over 1 day of operation. Improvements to the instability by several orders of magnitude are projected for future devices. We use the nuclear clock to constrain models of ultralight dark matter by searching for periodic fluctuations and slow drifts in the nuclear transition energy, on timescales between 20 s and 1 day. Benefitting from the enhanced sensitivity of the thorium-229 transition, these constraints compete with the best atomic clocks concerning dark matter coupling to photons and go beyond previous measurements regarding coupling to the strong force.

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Publication Details

Journal
Nature
Published
2026-10-07
DOI
https://doi.org/10.1038/s41586-026-11084-4
Citations
4
Primary Topic
Advanced Frequency and Time Standards
Type
article
Field-Weighted Citation Impact
11.44

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article

A thorium-229 optical nuclear clock with feedback loop

Thorsten Schumm, Georgy A. Kazakov, Martin Pimon, A. Hellerschmied et al.
4 citations
Nature
Advanced Frequency and Time Standards
11.44
article

A thorium-229 optical nuclear clock with feedback loop

Thorsten Schumm, Georgy A. Kazakov, Martin Pimon, A. Hellerschmied, Fabian Schaden, Maksim V. Okhapkin, Michael Bartokos, I. Morawetz, Heiner Denker, Johannes Tiedau, E. Peik, Michael Matus, Kjeld Beeks, Sebastian Lahs, G. Zitzer, L. Toscani De Col, Juliette Schlachet-Lépinay, M. (Martin) Čížek, O. (Ondřej) Číp, F. Schneider, N. Sempelmann, V. Lal, T. Lercher, V. Petrov, T. Riebner, B. Gerstenecker, A. Niessner, J. Premper
article en
4 citations

Abstract

Abstract The laser-accessible nuclear transition in the thorium-229 isotope has been identified as a candidate for realizing an optical nuclear clock 1 that might outperform current optical clocks based on electron-shell transitions in atoms or ions 2 . It is expected to be more robust against external perturbations 3,4 and to provide enhanced sensitivity in clock-based tests of the fundamental principles of physics 5,6 . Here we realize a thorium-229 nuclear clock by stabilizing a continuous-wave laser to the 148-nm nuclear transition with rapid feedback based on absorption spectroscopy 7 . The thorium-229 nuclei are embedded in a millimetre-sized, room-temperature calcium fluoride crystal. A subharmonic of the 148-nm radiation is continuously compared with a Yb + single-ion clock. The nuclear clock shows a shot-noise-limited fractional frequency instability of $$3\times 1{0}^{-12}/\sqrt{\tau /{\rm{s}}}$$ 3 × 1 0 − 12 / τ / s where τ is the averaging time, approaching 10 −15 instabilities over 1 day of operation. Improvements to the instability by several orders of magnitude are projected for future devices. We use the nuclear clock to constrain models of ultralight dark matter by searching for periodic fluctuations and slow drifts in the nuclear transition energy, on timescales between 20 s and 1 day. Benefitting from the enhanced sensitivity of the thorium-229 transition, these constraints compete with the best atomic clocks concerning dark matter coupling to photons and go beyond previous measurements regarding coupling to the strong force.

Nature
Leibniz University Hannover (DE), Physikalisch-Technische Bundesanstalt (DE), TU Wien (AT), Federal Office of Metrology and Surveying (AT), Vienna Center for Quantum Science and Technology (AT), Czech Academy of Sciences, Institute of Scientific Instruments (CZ), Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy (DE), Wolfgang Pauli Institute (AT)
European Commission, Deutsche Forschungsgemeinschaft, Austrian Science Fund, Defense Advanced Research Projects Agency, HORIZON EUROPE Framework Programme
Openalex Percentile: Top 1%
Advanced Frequency and Time Standards
11.44
DOIOpen Access PDFOpenAlex
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