Vienna and Beijing teams independently achieve world's first operating nuclear clocks

Two research teams working on opposite sides of the world have independently built what scientists are calling the first operating nuclear clocks—a breakthrough that could reshape how we measure time and what we can learn about the universe itself.

The Vienna team, led by physicist Thorsten Schumm at TU Wien, and the Beijing team, led by physicist Shiqian Ding at Tsinghua University, each arrived at functioning nuclear clocks using different technical methods. That they reached this milestone separately and nearly simultaneously matters more than it might seem. It suggests the underlying concept is solid, not dependent on one lab's particular tricks or equipment. Schumm, who has been pursuing this goal since 2008, calls it encouraging. Ding notes that physicists have been dreaming of nuclear clocks for nearly fifty years.

The name is misleading. These clocks are not powered by nuclear reactions. Instead, they work by using powerful lasers to track how light interacts with the nucleus of an atom—specifically, with thorium-229 isotopes embedded in solid calcium fluoride crystals. This is fundamentally different from conventional atomic clocks, which measure time by monitoring electrons as they jump between energy levels in an atom's outer shell. By measuring transitions inside the nucleus itself rather than in the electron shell surrounding it, nuclear clocks can theoretically achieve far greater precision. A nucleus is vastly smaller than the electron shell, which means the measurements can be correspondingly finer.

The best conventional atomic clocks today can run for billions of years while losing or gaining only a single second. These instruments have been essential to modern life—they keep global navigation satellites synchronized, they anchor the internet, they coordinate cellular networks and fiber-optic communications. Nuclear clocks, once fully developed, promise to do the job even better. They may also be built smaller and more robust than today's delicate atomic clocks.

But the technology is still rough. Schumm is candid about this: the Vienna clock remains far from its target performance. The researchers are still in the phase of perfecting the fundamental design. Yet there is already a path forward. The Vienna team has produced thorium crystals with higher concentration and better optical properties than Beijing's. The Beijing team has built a more powerful laser. Schumm sees the obvious next step: combine the best components from both labs to build a significantly better clock.

Beyond timekeeping, nuclear clocks open a door to new physics. The Vienna team used their clock to attempt a precision experiment aimed at detecting dark matter—the invisible substance that makes up most of the universe but has never been directly observed. The experiment did not find dark matter, but the nuclear clock performed at the level of the world's best atomic clocks, proving it could handle the demands of cutting-edge physics research. Schumm describes it simply: the technology gives access to a whole new physics universe. Applications Schumm envisions include satellite-based navigation, synchronization of data transfer, surveying, and metrology—the science of measurement itself. What began as a fifty-year dream is now a working instrument in two laboratories, each with something the other needs, each pointing toward a future where time itself can be measured with unprecedented precision.