Scientists Demonstrate First Operational Nuclear Clock Using Thorium-229
Two research groups — one European, one Chinese — have independently demonstrated the first operational nuclear clocks, using thorium-229 nuclei embedded in calcium fluoride crystals as frequency references. Nuclear clocks have been a theoretical goal for over two decades, with the key enabling discovery of thorium-229's laser-accessible nuclear transition made in 2023. The milestone extends precision timekeeping from electronic to nuclear transitions, opening potential applications in compact clocks, dark matter searches, and tests of fundamental physics.
Both teams, one led by Thorsten Schumm at TU Wien in Austria and one by a large Chinese collaboration, published preprints on arXiv in early June 2026 reporting the first clock operation based on the isomeric nuclear transition in thorium-229. The clocks work by embedding thorium-229 in calcium fluoride crystals and locking a vacuum-ultraviolet laser to the nuclear transition frequency, using a feedback loop to correct any frequency drift — the critical step that distinguishes a true clock from a mere spectroscopic demonstration. The Chinese team reports a fractional frequency instability of 2×10⁻¹² per square root of averaging time in seconds, and found that two separate crystals agreed at the 10⁻¹³ level, demonstrating reproducibility. The European team additionally used the clock to set new constraints on ultralight dark matter, exploiting the nucleus's high sensitivity to subtle changes in fundamental constants. Unlike conventional optical atomic clocks, the solid-state nuclear clock operates at room temperature without requiring ultracold atoms or vacuum systems, making it far more amenable to miniaturization. Current stability is still below the best optical atomic clocks — roughly tens of seconds lost per billion years versus a few seconds per billion years for leading atomic clocks — but researchers describe this as an early proof-of-principle with rapid improvement expected as laser and crystal technologies mature. The work is described as the culmination of 15–20 years of research and represents a fundamental shift in quantum metrology from electronic to nuclear transitions.
What's missing
No timeline is given for when nuclear clocks might be deployed in practical applications such as satellite navigation.
How coverage differed
New Scientist and Gizmodo both cover the story accurately, but New Scientist focuses primarily on the European (TU Wien) team and quotes its members extensively, while Gizmodo more explicitly highlights that two independent teams — European and Chinese — achieved the result simultaneously, giving a broader picture of the competitive landscape.
What different sources said
- arXiv physicsCenter
A nuclear clock based on $^{229}$Th
- Phys.orgCenter
Nuclear clocks tick for the first time
- New ScientistCenter
First working nuclear clock heralds a new era in timekeeping
- GizmodoCenter
Physicists Just Built the First-Ever Nuclear Clock
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