A breakthrough decades in the making has redefined timekeeping. Using thorium-229, physicists have constructed the first clocks that track energy shifts within an atomic nucleus rather than electron oscillations.
The milestone was reached independently by two separate teams. One group was led by the Technical University of Vienna, and the other by Tsinghua University. Both embedded thorium-229 nuclei in calcium fluoride crystals and excited them with vacuum-ultraviolet lasers.
Nuclear clocks promise superior stability because the nucleus is shielded from environmental interference that disturbs electrons in standard atomic clocks. This physical isolation makes the devices powerful candidates for detecting dark matter or testing if nature's fundamental constants shift.
The European device operated as a fully stand-alone clock, continuously stabilizing its laser frequency. It ran against a ytterbium-ion clock and set new constraints on ultralight dark matter models. The Chinese team focused on reproducibility, testing their system across different crystal samples and finding nearly identical frequencies. This agreement suggests solid-state nuclear clocks can become universal standards.
These first-generation devices do not yet beat the best atomic clocks, which have a 70-year head start. But they prove the concept is no longer theoretical. Experts predict they could surpass current precision benchmarks within a few years.