Two research groups have unveiled the world's first nuclear clocks. These devices utilize energy transitions within the nucleus of the thorium-229 atom, rather than electrons as seen in conventional atomic clocks.
A European team led by Thorsten Schumm from TU Wien and a Chinese group under Shiqian Ding at Tsinghua University in Beijing published their preprints on arXiv on June 3 and June 7, 2026. Both teams successfully "locked" a laser frequency to a nuclear transition, ensuring the clocks maintain their precision over time.
Nuclear clocks promise to be more robust and portable. The atomic nucleus is better shielded from external interference than electrons. Thorium-229 possesses such low transition energy that it can be triggered by an ultraviolet laser—a rare property among chemical elements.
The key involves monitoring the absorption of laser light by the atoms. When the frequency matches, the signal weakens; if it deviates, it strengthens, and the laser is immediately adjusted. The Chinese setup employs a more powerful laser with a lower concentration of thorium in the crystal, yet the signals from both teams proved comparable.
Work on nuclear clocks has been underway for over twenty years. In 2024, scientists first induced a nuclear transition within a crystal and precisely determined its frequency. Now, these clocks have become functional instruments that can be utilized to search for new physics.
What this will yield in the future is a question that physicists are only just starting to investigate. For now, one thing is clear: nuclear clocks provide a new way to look inside the atomic nucleus and test the fundamental forces of nature.
