Scientists Achieve Breakthrough with First Nuclear Clocks Using Thorium-229

Two international research teams have successfully created the world's first functioning nuclear clocks, marking a major breakthrough in precision timekeeping technology. The European team, led by Thorsten Schumm at Vienna University of Technology, and a Chinese team led by Shiqian Ding at Tsinghua University in Beijing independently developed these devices, with their findings posted to the preprint server arXiv in early June 2026.

Unlike traditional atomic clocks, which measure time using oscillations of electrons jumping between energy levels, nuclear clocks derive their 'tick' from fluctuations in the energy states of thorium-229 nuclei. The protons and neutrons within these nuclei can be boosted to higher energy states using ultraviolet laser light. Thorium-229 is uniquely suited for this application because its stable nuclear energy levels are close enough together that relatively modest ultraviolet light can trigger transitions between them—a property that other elements lack.

The central challenge in developing nuclear clocks was maintaining frequency stability to prevent the clock's tick from drifting over time. Both teams solved this problem by monitoring how much laser light was absorbed by thorium-229 atoms. When the laser frequency is optimal, photons are absorbed and the signal strength dips; if the frequency drifts, the signal increases again, allowing for immediate correction. The European and Chinese teams employed slightly different technical approaches: the Chinese group used a laser approximately 100 times more powerful but compensated with a lower concentration of thorium-229 atoms in their crystal, resulting in comparable overall signal quality.

Nuclear clocks offer several significant advantages over current technology. Nuclei are inherently more robust and harder to perturb than electron shells, and they are protected within crystal structures, making nuclear clocks potentially more portable and stable than the best existing atomic clocks. Beyond timekeeping applications, these devices provide physicists with an unprecedented tool to probe nuclear forces and search for new physics phenomena. Thorsten Schumm described the achievement as "a dream come true" after more than 20 years of theoretical and experimental development, while theoretical physicist Gilad Perez noted that nuclear clocks have transitioned from a concept with "potential" to "a functioning precision instrument."