Vienna and Beijing Scientists Achieve Breakthrough with World's First Nuclear Clocks

Two research teams working on opposite sides of the world have built something physicists have been chasing for nearly half a century: the first functioning nuclear clocks. Scientists in Vienna and Beijing announced their achievement on October 7, publishing separate papers in the journal Nature describing devices that represent a fundamental leap forward in how we measure time and what we might learn about the universe itself.

The clocks are not powered by nuclear reactions, despite what the name might suggest to the uninitiated. Instead, they work by using powerful lasers to track the behavior of light as it interacts with the nucleus of thorium-229 atoms, which the researchers have trapped inside solid calcium fluoride crystals. This is a departure from conventional atomic clocks, which have been the gold standard since 1949. Those older devices measure time by monitoring how electrons—the particles that orbit an atom's nucleus—jump between different energy levels when hit with lasers or microwaves. The Vienna and Beijing teams have gone deeper, literally into the nucleus itself, where protons and neutrons reside.

The theoretical advantage is elegant: a nucleus is vastly smaller than the electron shell surrounding it, so tracking transitions at that scale could theoretically yield even greater precision than the best conventional atomic clocks, which are already so accurate they would lose or gain only one second over billions of years. That kind of accuracy has already transformed modern life, underpinning everything from GPS navigation to the internet to cellular networks and fiber-optic communications.

What makes this moment particularly striking is that the two teams reached their goal independently and simultaneously, using different experimental approaches. Thorsten Schumm, a physicist at TU Wien in Austria who led the Vienna effort, noted that his team has been working toward this milestone since 2008. Shiqian Ding, a physicist at Tsinghua University in China who helped lead the Beijing team, emphasized that the parallel success proves the concept is robust—not dependent on any single technical method or laboratory setup. The fact that two separate groups solved the problem at the same time suggests the path forward is solid.

But both teams are clear-eyed about where they stand. The nuclear clocks do not yet outperform the best conventional atomic clocks, and Schumm described the Vienna device as still being "far from its target performance." The researchers are already plotting how to improve. Schumm noted that the Vienna team has produced thorium crystals with higher concentration and better optical properties, while the Beijing team has built a stronger laser. Combining those strengths—better crystals from Vienna, more powerful laser from Beijing—could yield a significantly more capable clock.

Beyond timekeeping, the nuclear clocks open a door to new physics experiments. The Vienna team used their clock to attempt a precision measurement aimed at detecting dark matter, the invisible substance that makes up most of the universe's mass but has never been directly observed. The experiment did not find dark matter, but the clock performed at the level of the best atomic clocks available, demonstrating its capability as a research instrument. Schumm described the potential as giving "access to a whole new physics universe." The applications Schumm envisions range from satellite navigation and data synchronization to surveying and metrology—the science of measurement itself. For now, the work remains in the refinement stage, but the breakthrough is real: physicists have finally built the tool they have been imagining for decades.