First Functional Nuclear Clocks Built, Marking a Breakthrough in Timekeeping
Physicists in Europe and China have independently constructed the first functional nuclear clocks, using the nucleus of thorium-229 atoms to measure time. Both teams published their results in preprints on arXiv.
The Two Breakthroughs
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The European Team: Led by Luca Toscani De Col of the Technical University of Vienna, this group built a stand-alone clock that stabilized a laser frequency using the thorium-229 nucleus. They compared its performance against a ytterbium-ion atomic clock and used the device to search for ultralight dark matter, setting new constraints on certain theoretical models.
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The Chinese Team: Led by Beichen Huang of Tsinghua University, this group tested their clock in two independently produced crystals. The clocks yielded nearly identical frequencies, suggesting that solid-state nuclear clocks may be reproducible without individual calibration.
Background & Significance
Atomic clocks, first built in the 1950s, rely on electron transitions and can lose less than one second over billions of years. A nuclear clock uses transitions within the atomic nucleus, which is less susceptible to outside interference and could offer even greater stability.
Thorium-229 was identified in 2003 as a suitable candidate due to its low-energy nuclear transition. In 2024, researchers triggered this transition and achieved a 'tick'. The new work converts that into a fully functional timekeeping device.
The new nuclear clocks do not yet outperform the best atomic clocks, but they demonstrate that the concept is now practical and reproducible.