Scientists at the Vienna Center for Quantum Science and Technology, together with German collaborators, have built and launched the world’s first solid-state nuclear clock — a device that measures time using energy oscillations inside the atomic nucleus itself, rather than electron transitions used in conventional atomic clocks.
The clock relies on thorium-229, an isotope embedded in a calcium fluoride crystal at room temperature. A specialized ultraviolet laser excites the nucleus to a uniquely low energy state, creating a self-correcting feedback loop that locks the laser to the nuclear transition frequency. What makes this instrument extraordinary is its extreme sensitivity to changes in fundamental physical constants — meaning it can detect fluctuations that no other timekeeping device can.
Within just 24 hours of continuous operation, the team already used the clock to search for ultralight dark matter — the invisible substance believed to make up most of the universe’s mass. While dark matter was not detected, the experiment set the tightest constraints yet on how it might interact with ordinary matter and light. The researchers plan to boost laser power in future iterations, potentially surpassing the best quantum standards within months.
The concept was first proposed in 2003, but it took over two decades to precisely measure the nuclear transition energy and build compatible lasers. The first successful excitation of thorium-229 was only achieved in 2024. Published in Nature on October 8, 2026.
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