For the first time, researchers from two teams have reported the successful operation of nuclear clocks, marking a significant breakthrough in physics.
Reporting their achievements in separate papers recently published in Nature, the European and Chinese teams have pushed the boundaries of atomic clock technology, building on decades of research to open an important new avenue for particle physics research.
Traditional atomic clocks operate by monitoring the energy transitions in the electrons surrounding an atom’s nucleus, while nuclear clocks measure time using energy transitions within the nucleus itself. One team was led by Thorsten Schumm of the Vienna University of Technology and Ekkehard Peik of PTB, Germany’s National Metrology Institute, while the other was led by Shiqian Ding of China’s Tsinghua University.
Nuclear Clock Technology
The new nuclear clocks represent a major step forward for the technology, although more work remains. Compared to traditional atomic clocks, these early nuclear clocks are less stable. However, while the technology has significant room for improvement, it holds promise for important practical applications and offers new ways to investigate fundamental physics.
Researchers hope continued development will improve the devices’ resilience while reducing their size. This could eventually allow physicists to conduct important research without the demanding ultrahigh-vacuum chambers and laser-cooling systems required by some conventional atomic clocks.
Finding the Right Element
Optical atomic clocks use a laser frequency stabilized to an atomic transition as a reference for keeping time. Nuclear clocks take this concept a step further, using transitions between quantum states within an atomic nucleus to establish their tick. This offers a major potential advantage over optical atomic clocks, as the tiny nucleus is far less susceptible to external disturbances, shielded by the surrounding electrons. Nuclear transitions can also produce exceptionally narrow spectral lines, providing a precise reference for the clock’s frequency.
Despite these potential benefits, researchers have long struggled to identify a suitable nuclear transition to serve as a reference. After studying numerous elements, scientists settled on thorium-229 because of the unusually low energy of its first excited nuclear state, which allows the transition to be driven using laser light.
Even after identifying thorium-229 as a promising candidate, researchers spent two decades studying the isotope’s excited nuclear state and gathering the necessary data. In 2024, they achieved a breakthrough by driving the transition with laser light for the first time and precisely measuring its frequency. Although this established the isotope’s viability for nuclear clock applications, using the nuclear transition to stabilize the laser remained out of reach.
Solving the Nuclear Clock
As sometimes happens in science, two independent teams solved this problem at approximately the same time. Both successfully stabilized the laser used by their clocks to the nuclear transition.
Each team developed a distinct approach. The European researchers had greater access to thorium, allowing them to build a device containing more thorium nuclei while using a lower-powered laser. The Chinese team took the opposite approach: Limited thorium availability led them to use a higher-powered laser to interact with a smaller quantity of the element.
“Ideally, we would like to combine the advantages of both approaches: high VUV [vacuum-ultraviolet] power and more thorium nuclei,” Ding explained. “If we can achieve both, the clock stability can improve substantially.”
While the Chinese team’s clock demonstrated better performance than its European counterpart, both remain less stable than today’s leading atomic clocks. The new devices would accumulate roughly one second of timing error over millions of years, compared with billions of years for the best conventional atomic clocks.
The technology still has room for further refinement, although the European team is already applying its technology to the search for dark matter. From improving timekeeping technology to potentially uncovering new physics, nuclear clocks represent an exciting area of research to watch.
The papers, “A Thorium-229 Optical Nuclear Clock with Feedback Loop” and “A Nuclear Clock Synchronized to 229Th,” both appeared in Nature on October 7, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.