Independent research teams in Beijing and Vienna have unveiled the world’s first working thorium-229 nuclear clocks, marking a major leap in precision timekeeping. Published on October 7, 2026, in the journal Nature, the breakthrough devices track quantum states inside atomic nuclei rather than electron shells, promising future accuracy that could surpass current atomic clocks.
Tsinghua University and Vienna Teams Build First Operating Nuclear Clocks
Timekeeping has officially entered its nuclear age. Two independent research groups—one led by associate professor Tsinghua University physicist Ding Shiqian in Beijing, and another involving the Vienna Center for Quantum Science and Technology in Austria—have successfully constructed operational nuclear clocks. Both systems rely on a specific isotope, thorium-229, embedded inside crystals to measure time through the steady rhythm of an atom’s core.
For more than two decades, physicists have theorized about building clocks based on nuclear transitions rather than electronic ones. Regular atomic clocks, which have defined the global standard for over 70 years, track changes in electrons surrounding an atomic nucleus using lasers or microwaves. Those electron shells, however, are easily disturbed by room temperature changes and ambient electric or magnetic fields.
The nucleus offers a vastly more stable foundation. Because a nucleus is thousands of times smaller than the surrounding electron cloud and tightly bound, it remains heavily shielded from external interference. Until recently, accessing those nuclear states required energetic X-rays or gamma rays that were impossible to harness with narrow-linewidth lasers.
How Thorium-229 Unlocked Nuclear Timekeeping
The entire endeavor hinges on a unique property of thorium-229. Its first excited nuclear state lies just 8.4 electron volts above the ground state, creating a transition energy low enough to be triggered directly by an ultraviolet laser.
That specific advantage was proposed in 2003, but experimental realization required solving immense technical hurdles. The turning point arrived in 2024, when researchers first drove the thorium-229 transition directly with laser light.
- The Beijing team developed a continuous-wave vacuum-ultraviolet laser operating at a wavelength of 148.4 nanometres, using it to trigger transitions in thorium-229 embedded within crystals.
- The Vienna researchers used thorium crystals at a higher concentration and with superior optical properties, linking their clock to an atomic clock through six miles of optical fiber.
- Both teams implemented feedback loops where ultraviolet lasers continuously irradiated the thorium nuclei, checking excitation rates and using corrections to counteract any frequency drift.
China Timepiece Claims Stability Edge in Parallel Development
Initial results published in Nature show that the two instruments operate at broadly comparable performance levels, though initial testing indicates the Tsinghua University system is about six times as stable as the European counterpart.
The Beijing researchers also demonstrated that two separately grown crystals kept the same time, suggesting the core timing signal does not depend on a single anomalous crystal.
There was no single step that suddenly made the clock possible. The problems included making a material with the right clock nuclei inside it and developing lasers precise enough to produce reliable changes.
Shiqian Ding, Tsinghua University physicist and study co-author
Meanwhile, the Vienna team put their prototype to work immediately. Thorsten Schumm and his colleagues ran their nuclear clock alongside a ytterbium atomic clock to search for dark matter. Because atomic and nuclear clocks react differently to fluctuating fundamental physics constants, tracking changes in their relative tick rates offers a sensitive probe for invisible matter.
While that initial dark matter search did not detect a positive signal, the experiment proved the clock’s capability to constrain models of ultralight dark matter.
Next Steps for Portable Precision and Fundamental Physics
Neither prototype has surpassed the raw precision of the world’s most advanced atomic clocks yet. Measured in accumulated error, the nuclear clocks are so accurate that if they ran for 30 million years, they would only be off by a second. By comparison, top ytterbium atomic clocks miss just one second every 23 billion years.
However, scientists emphasize that the architecture is now proven. With continued upgrades to laser power, crystal quality, and thorium concentration, researchers expect future generations of nuclear clocks to outperform atomic timekeepers.
We envision a chip-scale device. Thorium-229 had potential to be more stable than atomic clocks, meaning nuclear clocks could become very small and practical to move around.
Thorsten Schumm, TU Wien physicist and European team member
Both research groups plan to continue refining their hardware and collaborating on future findings.