ScienceNot yet confirmed elsewhere1 publisher2 min readPublished
TU Wien's thorium nuclear clock runs on its own for more than a day
TU Wien physicists have built a thorium nuclear clock that held its own laser steady for more than 24 hours without leaning on a conventional atomic clock. The university's release reports how long it ran but not how precisely it ticked, and that figure would show whether thorium can compete with today's atomic clocks.
The Scientist · Science desk
Evidence map. Supported: TU Wien built what it calls the first self-stabilizing nuclear clock, which ran for more than 24 hours on its own. Contested: the release gives no stability or uncertainty figure. Insufficient: nuclear clocks may one day beat atomic clocks.
- Supported A team in Vienna (TU Wien) has built what the release calls the world's first self-stabilizing nuclear clock., claim 1
- Supported Unlike earlier prototypes, the nuclear clock can maintain its own stability without depending on a conventional atomic clock, and researchers demonstrated it can operate steadily for more than 24 hours without intervention., claim 2
- Contested The release describes the clock's performance by its run duration (more than 24 hours without intervention) and does not state a frequency stability or uncertainty figure., claim 14
- Insufficient evidence The release says nuclear clocks could eventually measure time with far greater precision than today's most advanced atomic clocks, using nuclei as exceptionally stable references., claim 15
| Claim | State | Claim number |
|---|---|---|
| A team in Vienna (TU Wien) has built what the release calls the world's first self-stabilizing nuclear clock. | Supported | 1 |
| Unlike earlier prototypes, the nuclear clock can maintain its own stability without depending on a conventional atomic clock, and researchers demonstrated it can operate steadily for more than 24 hours without intervention. | Supported | 2 |
| The release describes the clock's performance by its run duration (more than 24 hours without intervention) and does not state a frequency stability or uncertainty figure. | Contested | 14 |
| The release says nuclear clocks could eventually measure time with far greater precision than today's most advanced atomic clocks, using nuclei as exceptionally stable references. | Insufficient evidence | 15 |
What happened
- The device is built around a crystal containing thorium atoms, made at TU Wien, with a laser shone onto the nuclei inside it.
- In April 2024, Thorsten Schumm's TU Wien group and Ekkehard Peik's team at PTB Braunschweig first excited thorium nuclei with laser light.
- That fall, the researchers linked their thorium apparatus to a conventional optical atomic clock to show the nuclei could serve as a precise timing reference.
Why it matters
- capability A nuclear transition can now correct a drifting clock laser, the job electron transitions do in atomic clocks, so thorium clocks can be built and run as standalone instruments.
- constraint Until stability and uncertainty figures appear, the 24-hour run shows endurance only and cannot be ranked against optical atomic clocks.
- precedent With a standalone thorium clock built, the claim that nuclear timekeeping can eventually outdo atomic clocks can be tested by direct comparison, and we'd expect that comparison to be the next result reported.
"What you really want is a self-stabilizing nuclear clock," said Thorsten Schumm, whose group at TU Wien's Institute of Atomic and Subatomic Physics built the device [8][1][5]. "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." [8]
The laser is the part that ticks, and its frequency drifts. "The oscillation of this laser light can be used for timekeeping, but the laser frequency can shift slightly from time to time, for example due to temperature fluctuations," Schumm said [10]. A conventional atomic clock corrects the laser against an energy transition in an atom's electrons. The Vienna team has shown that a transition in the thorium nucleus can do the same job [11].
Few nuclei could do it. Changing a nucleus's energy state usually takes far more energy than a laser can supply, but two of thorium's nuclear states sit unusually close together, so laser light can drive the transition between them [4]. The release says the nucleus is also far less sensitive to outside disturbances than the electrons that current clocks rely on [3]. It rests its prediction that nuclear clocks could eventually measure time far more precisely than today's best atomic clocks on that stability [15].
According to the release, the 2024 experiments established the principle but left the clock unable to keep its own accuracy independently [7]. The announcement of the self-stabilized version is dated October 10, 2026, about 30 months after the first laser excitation of a thorium nucleus [13].
The thing this doesn't tell you is how good the clock is. Running steadily for a day without intervention shows that the lock holds [2]. How far the frequency moved within that day is a separate measurement, and we think it is the one that decides whether a clock can serve as a time standard. The release describes the result by its duration and does not give a stability or uncertainty figure [14].
What to watch
- Whether the clock holds its lock for weeks, and through the temperature swings Schumm named as a cause of laser drift.
- Whether PTB Braunschweig, Schumm's 2024 partner, or another lab reproduces self-stabilized operation with independently grown thorium crystals.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence40
- Adoption
- Insufficient
- Hype gap+35
- Incentives55
- Confidence45
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A team in Vienna (TU Wien) has built what the release calls the world's first self-stabilizing nuclear clock.
- [2]
Unlike earlier prototypes, the nuclear clock can maintain its own stability without depending on a conventional atomic clock, and researchers demonstrated it can operate steadily for more than 24 hours without intervention.
- [3]
The clock uses the nuclei of thorium atoms, which the release says are far less sensitive to outside disturbances than the electrons in atoms used by atomic clocks.
- [4]
Moving a nucleus between energy states typically requires enormous energy; thorium is an exception, with two nuclear energy states separated by an unusually small gap, making it possible to trigger the transition with laser light.
- [5]
In April 2024, researchers led by Prof. Thorsten Schumm at TU Wien's Institute of Atomic and Subatomic Physics, working with a team led by Prof. Ekkehard Peik at PTB Braunschweig, identified the thorium nuclear transition experimentally and showed for the first time that laser beams could excite thorium nuclei.
- [6]
In the fall of 2024, the researchers connected their thorium excitation apparatus to a conventional optical atomic clock, demonstrating that the nuclei could serve as a highly precise timekeeping reference.
- [7]
The release says the 2024 work established the basic principle of a nuclear clock but was missing the ability to maintain its own accuracy independently.
- [8]
"What you really want is a self-stabilizing nuclear clock. 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."
ReportedSupportedSource: Thorsten Schumm, TU Wien, quoted in the university releaseView cited source - [9]
The system is built around a special crystal containing thorium atoms, manufactured at TU Wien; a laser shines onto the crystal and interacts with the thorium nuclei inside.
- [10]
"The oscillation of this laser light can be used for timekeeping, but the laser frequency can shift slightly from time to time, for example due to temperature fluctuations."
ReportedSupportedSource: Thorsten Schumm, TU Wien, quoted in the university releaseView cited source - [11]
Traditional atomic clocks keep the laser frequency stable using energy transitions of electrons in atoms as a reference; the Vienna team has demonstrated that thorium nuclei can perform the same function.
- [13]
The October 10, 2026 release came about 30 months after the April 2024 first laser excitation of thorium nuclei.
- [14]
The release describes the clock's performance by its run duration (more than 24 hours without intervention) and does not state a frequency stability or uncertainty figure.
- [15]
The release says nuclear clocks could eventually measure time with far greater precision than today's most advanced atomic clocks, using nuclei as exceptionally stable references.
ReportedInsufficientSource: Vienna University of Technology release2 sources— create a free account to open themView cited source
Sources
1 independent publisher whose own reporting we read for this story.
- sciencedaily.comScientists build a nuclear clock that could make atomic clocks obsolete
1 article · October 10, 2026
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