The best timekeepers today—atomic clocks—work off the quantum vibrations of an atom, specifically its electrons. But physicists have long dreamt of even better clocks that run on atomic nuclei, which are less sensitive to environmental disturbances. According to new research, that dream might soon become reality.
Last week, two independent teams based in Europe and China reported the first set of results from experiments using an atomic nuclei clock based on crystals of calcium fluoride containing thorium-229. Both papers, which have yet to be peer reviewed, are available as a preprint on arXiv. In the European experiment, researchers compared how well the clock fared against leading atomic clocks involved in the search for dark matter. The Chinese team, on the other hand, demonstrated the clock’s operation to compare its performance with atomic clocks.
“These results establish a solid-state platform for compact nuclear clocks, nuclear quantum sensing, and precision tests of fundamental physics,” the European team wrote in its paper.
Advanced timekeeping
According to a column by physicists Eric Hudson and Andrei Derevianko, ultraprecise clocks are “more than scientific curiosities,” as they are vital for smooth navigation, communications, and international timekeeping. Hudson and Derevianko, from the University of California, Los Angeles, and the University of Nevada, Reno, respectively, contributed to research from last December that demonstrated the potential of thorium-229 in atomic nucleus clocks.
In atomic clocks, scientists zap and excite the electrons in an atom to push the electrons from one energy level to another. That absorption “happens at an exquisitely precise frequency,” they explained, adding that these patterns are “set by the laws of physics” and give the world a fairly consistent standard for keeping time.
Meanwhile, a nucleus is 10,000 times smaller than an atom and less prone to disturbances from temperature, electric fields, and other environmental disturbances, the pair wrote—hence, physicists’ long-time interest in atomic nucleus clocks.
A concept comes to life
The challenge, then, was to find an atom that scientists could most effectively manipulate. For instance, it should be responsive to the laser that scientists use to trigger the “ticks,” so to speak, to tell time. In that sense, thorium-229 was an “exceptionally rare case” in which it has two different states, which scientists can induce using lasers to excite the nucleus from one state to another, explained Hudson and Derevianko.
The latest pair of papers build upon their work, among many others from the past couple decades. Importantly, the recent demonstrations implement a feedback loop that stabilizes the clock’s operations. This represents an improvement from the European team’s own work from 2024 and 2025.
“This was the final missing step before calling it an actual clock,” Lars von der Wense, a physicist at Johannes Gutenberg University Mainz in Germany, told Science News. With forthcoming improvements to laser and crystal technology, nuclear clocks should advance rapidly, added von der Wense, who wasn’t involved in either work.
At the frontier of physics
Setting aside nuclear clocks’ practical benefits, researchers believe they could test the fundamental constraints of nature and new physics, according to Hudson and Derevianko. And indeed, that’s what the European team immediately set out to do with its latest iteration of a nuclear clock. The latter half of its paper describes how well the clock fared in evaluating constraints for ultralight dark matter—a hypothetical form of matter that could explain a whole bunch of cosmic mysteries.
To Science News, Thorsten Schumm, a physicist at TU Wien in Austria from the European team, reported that the nuclear clock already outperformed all atomic clocks in certain types of measurements. All that said, the technology is still at its first stages, he added. But it looks like nuclear clocks are off to a good start.
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