Plate Nº 67 · recorded October 10, 2026
PhysicsReported finding
Vienna hosts world's first self-stabilizing nuclear clock
A thorium-based nuclear clock at TU Wien has kept stable time for over 24 hours on its own, reaching a precision of one second per 30 million years, researchers report in Nature.
By James Calloway4 min read735 words
In brief
- The world's first self-stabilizing nuclear clock ran stably for more than 24 hours without intervention.
- Its precision is about 10^-15 — roughly one second of error per 30 million years.
- In April 2024, teams led by Thorsten Schumm (TU Wien) and Ekkehard Peik (PTB Braunschweig) first excited thorium nuclei with lasers.
- Atomic nuclei are over 10,000 times smaller than atoms and less sensitive to disturbances.
- The findings are published in Nature (2026), DOI: 10.1038/s41586-026-11084-4.
The world's first self-stabilizing nuclear clock has run continuously for more than 24 hours without human intervention, physicists at TU Wien report in the journal Nature. The prototype achieves a precision of roughly one second of error per 30 million years — about 10 to the power of minus 15 — marking the first time a clock has used atomic nuclei, rather than whole atoms, to regulate its own ticking.
The Vienna team, led by professor Thorsten Schumm at the Institute of Atomic and Subatomic Physics at TU Wien, built the device after a breakthrough in April 2024. In that earlier work, together with professor Ekkehard Peik's group at PTB Braunschweig, the researchers demonstrated for the first time that thorium nuclei can be excited with laser beams. By fall 2024 they had coupled the thorium apparatus to a conventional optical atomic clock — but that version still leaned on an ordinary atomic clock as a reference.
The new system stands alone.
Why thorium nuclei make good timekeepers?
For decades, physicists suspected that thorium atomic nuclei have a rare property: two energy states separated by an unusually tiny energy gap. Because that gap is so small, a laser can deliberately "switch" the nucleus from one state to the other. In other atomic nuclei, the energy gaps are much larger, so the nuclei simply do not respond to laser light.
That laser sensitivity is what turns a nucleus into a clock component. Atomic nuclei are more than 10,000 times smaller than atoms, Schumm explains, so they react far more weakly to external disturbances such as temperature changes. In principle, that makes them much more reliable timekeepers.
How does the clock stabilize itself?
At the core of the device sits a crystal containing thorium atoms, produced at TU Wien. A laser irradiates this crystal, and the oscillation of the laser light serves as the clock's ticking.
The problem is that laser frequencies drift. "The laser frequency can shift slightly from to time, for example due to temperature fluctuations," Schumm said. "For high-precision measurements, you therefore need a mechanism to keep the laser frequency exactly stable, so that the clock continues to tick with precisely the same rhythm."
Ordinary atomic clocks solve this with atoms and the energy states of their electrons. Schumm's team uses thorium nuclei instead. The nuclei absorb laser light only when the laser frequency is exactly right. If the frequency drifts even slightly, absorption drops measurably, and the system automatically readjusts the laser. The clock keeps ticking at the same rhythm — no external atomic clock required.
"What you really want is a self-stabilizing nuclear clock," Schumm said. "The basic idea is simple: you have a laser and you have thorium. The laser changes the energy state of the thorium nuclei, and the thorium nuclei are used to stabilize the frequency of the laser."
How precise is it — and what are the limits?
The researchers measured the clock's stability over the course of a full day. The result, roughly 10 to the power of minus 15, is impressive for a first prototype but still short of the world's best optical atomic clocks.
"This is not yet at the level of the world's best optical atomic clocks, but for a first prototype it is a fantastic result," Schumm said.
The team plans to push precision much higher through several improvements:
- stronger lasers
- better thorium crystals
Those steps matter because the technology could eventually surpass the precision of existing atomic clocks and enable a new kind of high-performance metrology — the science of measurement — allowing physical quantities to be measured with previously unattainable precision.
The findings are preliminary in the sense that this is a first-generation device: the current precision figure comes from a single day of monitoring, and the record-setting regime remains a goal rather than an achievement. Still, the rapid succession of advances since 2024 — from first excitation of the thorium transition, to a clock tethered to an atomic reference, to a fully self-regulating system — suggests the field is moving quickly.
Publication details
The results appear in two papers: Thorsten Schumm et al., "A thorium-229 optical nuclear clock with feedback loop," Nature (2026), DOI: 10.1038/s41586-026-11084-4, and I. Morawetz et al., "Continuous-wave laser absorption spectroscopy of the thorium-229 nucleus," Nature (2026), DOI: 10.1038/s41586-026-11011-7.
via Phys.org Physics (Source)
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