Physics

A thorium-229 optical nuclear clock with feedback loop

L. Toscani De Col, T. Riebner

Featured June 23, 2026

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Simply

A new type of clock using the nucleus of a thorium atom instead of electrons provides a more stable and precise way to measure time and search for mysterious dark matter.

In depth

The paper describes the first stand-alone nuclear clock by stabilizing a continuous-wave laser to the 148 nm nuclear transition of Th-229. By implementing a feedback loop based on continuous absorption spectroscopy, the system achieves long-term stability and enables sensitive searches for ultralight dark matter through periodic fluctuations in fundamental constants.

Key Takeaways

1
The authors demonstrate the first nuclear clock that operates as a self-contained device using a closed-loop feedback mechanism.
2
The system utilizes continuous absorption spectroscopy to overcome the limitations imposed by the long isomeric state lifetime of the Th-229 nucleus.
3
The clock provides competitive constraints on ultralight dark matter coupling to photons, quarks, and the strong force, surpassing previous atomic clock measurements in specific parameter spaces.

Conceptual Flow

HIGH LEVEL

Methodology: The Feedback Loop

The system uses a laser to probe the thorium crystal, measures the light absorbed, and automatically adjusts the laser frequency to stay perfectly locked to the nuclear transition.

Laser Light

Thorium Crystal

Measure Absorption and Adjust Frequency

Stable Clock Signal

Results: Dark Matter Search

By comparing the nuclear clock to an atomic clock, the researchers look for tiny, rhythmic changes in time that would reveal the presence of dark matter.

Nuclear Clock

Atomic Clock

Compare Frequencies

Dark Matter Limits