The World’s First Nuclear Clocks Are Ticking, Opening a New Way to Investigate Dark Matter and Other Mysteries of Physics

Two independent teams of scientists have created the first functional clocks that can keep ultraprecise time using the nuclei of a radioactive element

Sara Hashemi | Daily Correspondent

June 24, 2026 12:37 p.m.

metal pole with a cylindrical crystal illuminated in blue light — Crystal containing thorium-229 atoms used in the European team's clock TU Wien

For decades, scientists have tried to build a device even more precise than an atomic clock, which keeps time using electrons, the negatively charged particles that whiz around in an atom.

Now, two independent teams of physicists have finally made a giant leap toward that goal. They’ve created the world’s first functioning nuclear clocks, which rely on an atom’s core, or nucleus.

A group in Europe posted their study on the preprint server arXiv on June 3, and a group in China posted their work on June 7. The findings, none of which have been peer reviewed, have implications beyond timekeeping. Nuclear clocks can help scientists gain new insights into fundamental physics and search for dark matter, the invisible stuff thought to make up most of the matter in the universe.

“This is an outstanding result,” says Victor Flambaum, a theoretical physicist at the University of New South Wales in Sydney who was not involved in either study, to Science News’ Emily Conover about the European team’s paper. It demonstrated that their clock’s sensitivity to some dark matter was equal to or better than that of atomic clocks.

“This is only the first step,” Flambaum adds. The “race for building super-accurate nuclear clocks just started.”

In a conventional clock, time is often based on an oscillating mass, like the pendulum of a grandfather clock or a quartz crystal in a wristwatch. But these human-made objects are imperfect, since no two pendulums can be exactly alike. Instead, atomic clocks—which are currently the most precise timekeeping device we have—work by measuring the quantum energy levels of atoms to tell time.

When an atom gets excited by an external energy source, like a laser emitting a specific wavelength of light, some of its electrons jump to a higher energy state. When they fall back to their lower energy state, the atom releases energy at a precise frequency that can be used to keep time.

A nuclear clock works on the same basic principle but can be even more exact. It relies on transitions in the nucleus, which is made of positively charged protons and neutral neutrons. Because the nucleus is less affected by external influences like electromagnetic fields, nuclear clocks have the potential to be more precise than atomic clocks. Additionally, nuclear clocks can be more practical to work with, since they involve atoms encased in crystal at room temperature, while the best atomic clocks require atoms to be chilled and suspended in a vacuum chamber.

Did you know? Atomic clock timeline

American physicist Harold Lyons developed the first atomic clock, which used ammonia molecules. He unveiled it in 1949, although it was just as precise as traditional clocks. Six years later, English physicist Louis Essen publicly announced the first atomic clock, which relied on cesium, deemed stable enough to be used as a time standard.

Both the European and Chinese teams’ nuclear clocks use thorium-229, a rare version of the element thorium. Its nucleus needs a small amount of energy to get excited compared to other atoms, so it can be manipulated with ultraviolet laser light. Scientists first proposed that thorium-229 could be used to create a clock in 2003, but it took about two decades for researchers to get the atomic nuclei to flip between energy states.

To create a functional clock, however, they still needed to have lasers that emit the exact wavelength of light required to excite thorium-229 nuclei, which arrived with the advent of continuous-wave lasers.

“With the continuous lasers, we can measure the nucleus in absorption and get an immediate response, whether the laser is still at the right frequency (and if not, correct it back),” writes Thorsten Schumm, a physicist at the Vienna University of Technology in Austria and co-author of the European team’s paper, in an e-mail to Kenna Hughes-Castleberry at Live Science.

“Once we had that, it was ‘just’ implementing some electronics and atomization to have the clock stabilize itself to the nucleus.”

The clocks were built slightly differently, although their signals are comparable. The Chinese team’s device involves a more powerful laser than that of the other group, but the European team’s device contains a crystal with a lower concentration of thorium-229 atoms, reports Nature’s Elizabeth Gibney. Over the course of a day, the clocks’ timekeeping drifted by a tiny amount, roughly equal to one second in three million years, which is less stable than the best atomic clocks that are currently available.

Still, nuclear clocks could, in principle, become steadier than atomic clocks. And since they’re governed by protons and neutrons, stuck together via strong nuclear force, they can be used to study different theories of physics than atomic clocks, which are mostly subjected to electromagnetic forces. For instance, a nuclear clock can help researchers detect dark matter by picking up on fluctuations caused by the strange stuff that shift the device’s frequency.

Because of these grand possibilities, “nuclear clocks have become one of the most actively pursued frontiers,” Shiqian Ding, a physicist at Tsinghua University in China and co-author of the Chinese team’s paper, tells Science News.

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