Scientists at the Vienna Center for Quantum Science and Technology, together with German colleagues, have built and launched the world’s first solid-state nuclear clock — a device that tracks time using energy transitions inside the atomic nucleus rather than electron orbits. The clock relies on thorium-229, an isotope whose nucleus can be excited to a remarkably low energy level by a specialized ultraviolet laser. Researchers embedded thorium-229 particles in a millimeter-scale calcium fluoride crystal at room temperature and created a feedback system in which the laser automatically locks onto the nuclear transition frequency.
Unlike conventional atomic clocks, which measure time through electron transitions and are already extraordinarily precise, the nuclear clock is sensitive to changes in fundamental constants of the universe — variations that could reveal ultra-light dark matter or new physics beyond the Standard Model. Within just 24 hours of continuous operation, the device achieved record stability without requiring complex cryogenic cooling.
The idea of a thorium-229 clock was first proposed in 2003, but practical implementation took over two decades: scientists needed to precisely measure the nuclear transition energy and build suitable lasers. The first successful excitation of the thorium nucleus was achieved only in 2024. The results are published in Nature.
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