Two independent research groups in Vienna and Beijing have built the world’s first working nuclear clocks using thorium-229 crystals and ultra-precise lasers. Published on 7 October 2026, the breakthrough devices track quantum transitions inside atomic nuclei, achieving stability that could eventually surpass current cesium and optical atomic clocks.
Timekeeping has officially entered its nuclear age. Two separate teams of scientists — one stationed at the Vienna Center for Quantum Science and Technology in Austria and another at Tsinghua University in Beijing — have successfully constructed the world’s first working nuclear clocks. Their peer-reviewed results were published in Nature, marking a fundamental shift away from the electronic timekeeping standards that have governed global infrastructure for decades.
Originally invented in 1949 to measure time with high precision, atomic clocks avoid utilizing nuclear fission or fusion despite their name. Nuclear clocks sidestep this limitation by targeting a much smaller, more stable domain.
How Thorium-229 and Laser Feedback Drive the Vienna and Beijing Prototypes
Atoms consist of a dense nucleus surrounded by a spacious cloud of electrons. While atomic clocks track changes in those electron clouds, nuclear clocks use a similar logic but track even smaller changes in the nucleus of an atom. Thorium-229, a specific isotope of thorium, possesses the necessary characteristics to function as a timekeeper.
Triggering changes inside an atomic nucleus normally requires enormous amounts of energy. However, thorium-229 is a rare exception.
Both teams grew crystals containing thorium-229 and suspended them under ultra-precise lasers. Directing their efforts toward compact calcium fluoride crystals holding thorium-229, the team constructed a laser capable of producing ultraviolet light at 148.4 nanometres. The Vienna team embedded their thorium nuclei inside a calcium fluoride crystal maintained at room temperature, developing a feedback loop where the thorium-229 nuclei provide long-term frequency feedback to stabilise the laser that drives it. This self-stabilizing mechanism allows the device to operate independently for more than 24 hours without manual intervention.
“The basic idea is simple: you have a laser and you have thorium.”
Thorsten Schumm, Professor at the Vienna University of Technology
Tsinghua University physicist Beichen Huang and co-author Shiqian Ding pursued a parallel approach in Beijing. The Beijing clock, led by Beichen Huang and Shiqian Ding at Tsinghua University, took a different path by using a substantially more powerful laser and generating VUV light by heating cadmium vapor to approximately 600 degrees Celsius as part of their frequency conversion chain. Their crystal contained fewer thorium nuclei than Vienna’s, but the stronger laser more than compensated.
Performance Benchmarks and the Immediate Hunt for Dark Matter
The current clocks operate at roughly one part in ten to the fifteenth stability over 24 hours — extraordinary by everyday standards, but still short of the stability that today’s best atomic clocks achieve.
Commercial Nuclear Clock Deployment Remains Years Away
Researchers acknowledge that practical commercial deployment remains years away. Professor Schumm noted that nuclear clocks may eventually far surpass their atomic forebears, but they aren’t there yet.
Highlighting that commercial timing infrastructure will likely take a backseat to initial fundamental physics experiments, NIST stated in August 2026 that a nuclear clock surpassing top optical clocks is still several years away.
For now, university teams are pressing ahead with field expansions. Hoping that improved thorium crystals and stronger, more efficient lasers will continually boost precision for each successive model, Professor Schumm’s team and other international research groups are engaged in a fast-paced global competition to construct the initial nuclear clock that definitively beats current atomic timekeeping instruments.