Atomic clocks from Vienna: what has really been achieved and why atomic clocks aren’t going away just yet

The most accurate timekeepers humanity has are atomic clocks. Their principle has remained unchanged since the 1950s: they monitor how electrons behave within the atom’s shell. Scientists in Vienna have now unveiled a clock that takes its “tick” from the atomic nucleus. However, reports that this spells the end of atomic clocks and that the new ones are many times more accurate are premature. What has actually been achieved?

What happened

On October 7, 2026, the journal Nature published two papers on the first functioning nuclear clocks. One was prepared by Thorsten Schumm’s team at TU Wien in collaboration with the German National Metrology Institute (PTB), and the other by an independent team from Tsinghua University in Beijing. The Vienna result is described as the first standalone atomic clock that stabilizes itself without needing to reference other clocks.

How atomic clocks work

Atomic clocks maintain the laser’s frequency so that it precisely matches the transition of electrons between two energy levels. Nuclear clocks use the same principle, but operate based on a transition within the nucleus itself.

Why Thorium-229?

Nuclear transitions typically require enormous amounts of energy, which is why they cannot be controlled by a laser. The thorium-229 isotope is an exception: it has the lowest known energy of an excited nuclear state, approximately 8.4 eV, so it can be excited by light in the ultraviolet range. The concept of a nuclear clock based on this isotope was proposed in 2003 by Ekkehard Peik and Christian Tamm.

Crystal and Laser

Thorium nuclei are embedded in a calcium fluoride crystal measuring on the order of millimeters, which operates at room temperature. A continuous-wave laser with a wavelength of 148 nanometers is tuned to the frequency of the nuclear transition. The absorption signal is detected and serves as feedback to maintain the laser’s frequency. This closes the loop: the nuclei continuously control the laser, rather than the other way around.

What the classes have achieved

• The system ran continuously for more than 24 hours.
• Accuracy is specified at approximately 10 to the minus 15th power, which corresponds to a deviation of roughly one second every 30 million years.
• Contact with atomic clocks via optical fiber was also used to examine the clock’s behavior.

What it is not

They aren't many times more accurate

Sources are clear: the stability achieved still lags behind the best optical atomic clocks. The claim of a clock that is “many times more accurate” is therefore not valid. This is the first functioning device, not a record for accuracy. The goal is for atomic clocks to improve upon this foundation in the future.

Atomic clocks never stop

Current atomic clocks remain the most accurate instruments for measuring time, and claims about their obsolescence are unfounded. Nuclear clocks represent a new, complementary approach and will remain the subject of research for several more years.

These aren't exactly the very first nuclear clocks

The prototype, often referred to as the first atomic clock experiment, was demonstrated in 2024 by a team from JILA in the United States, which compared the frequency of thorium with that of strontium. A new development from 2026 is a closed-loop system in which the nucleus itself controls the laser.

Why atomic clocks might be interesting

• Lower sensitivity to interference. The nucleus is smaller and better protected than the electron shell, so it is expected to be less sensitive to external fields. This is a theoretical expectation, and further measurements are needed to confirm it.
• Solid-state design instead of a vacuum chamber. A crystal containing thorium nuclei could lead to more compact and portable clocks, although the current device is a laboratory prototype.
• Physics beyond the Standard Model. The nuclear transition is sensitive to possible changes in fundamental constants and is therefore also linked to the search for dark matter. According to information accompanying the preprint, the Vienna team has already conducted such a test with the clock.

Practical Applications

The areas mentioned include navigation and basic research. However, these are prospects, not products. According to general knowledge, thorium-229 is a rare radioactive isotope, and its availability is another limitation—this is our general observation, not a claim from published sources.

What is confirmed and what is not

• Confirmed: closed-loop feedback between the core and the laser, 24-hour operation, accuracy of about 10 to the minus 15th power, crystal at room temperature, publication in the journal Nature on October 7, 2026.
• Unconfirmed: “accuracy many times higher” than that of atomic clocks, the end of the atomic clock era, and practical application in the near future.

Conclusion

The Vienna atomic clock is an important milestone: for the first time, the atom itself stabilizes the laser, and the clock runs on its own. However, there is still a lot of work to be done to achieve the precision of the best optical clocks, so this new device does not spell the end of atomic clocks. It will be interesting to see how quickly stability can be improved and whether the technology will make the leap from the laboratory to practical application.