Overview
- The two independent teams published their results on Wednesday, October 7, 2026, in Nature, reporting functioning nuclear clocks that use the low-energy thorium-229 transition as the timing reference.
- Both prototypes embed thorium-229 in calcium-fluoride crystals and use narrow-linewidth continuous-wave ultraviolet lasers with a feedback loop that locks the laser to the nuclear absorption signal.
- The Vienna (PTB–TU Wien) system is the first self-stabilizing nuclear clock, ran stable for more than 24 hours, and demonstrated fractional precision around 10^-15 while being used to set limits on ultralight dark-matter couplings.
- The Tsinghua-led Beijing device produced higher interrogation power, showed about six times better short-term stability in early tests, and delivered reproducible clock signals across separately grown crystals.
- Neither prototype yet beats the best optical atomic clocks, and researchers say clear next steps—better host crystals, more powerful and narrower VUV/UV lasers, and trapped-ion implementations—could raise accuracy enough to enable compact precision timing, improved navigation and new searches for physics beyond the Standard Model.