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The first nuclear clocks are ticking in Vienna and Beijing
On October 7, 2026, teams at TU Wien and Tsinghua University reported the first working thorium 229 nuclear clocks in Nature. The clocks use laser driven transitions inside thorium nuclei embedded in calcium fluoride crystals, rather than the electron transitions used by conventional atomic clocks.
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Key takeaways
- On October 7, 2026, teams at TU Wien and Tsinghua University reported the first working thorium 229 nuclear clocks in Nature.
- The clocks use laser driven transitions inside thorium nuclei embedded in calcium fluoride crystals, rather than the electron transitions used by conventional atomic clocks.
- Vienna demonstrated more than 24 hours of self stabilizing operation; Tsinghua reported roughly six times greater frequency stability and closely matching readings from separately grown crystals.
- The results establish a working proof of principle, not a new accuracy record: the prototypes have not been shown to outperform the best atomic clocks.
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openai.comCreate a landscape editorial hero image for this Studio Global article: What did the independent TU Wien and Tsinghua University teams in Vienna and Beijing report in Nature on October 7, 2026, about the world’s. Article summary: The independent Vienna and Beijing teams reported the first operating thorium-229 nuclear clocks in Nature on October 7, 2026—a milestone in turning a nuclear transition into a working timekeeping reference, rather than . Topic tags: general, education, general web, news, academic. Style: premium digital editorial illustration, source-backed research mood, clean composition, high detail, modern web publication hero. Use reference image context only for broad subject, composition, and topical grounding; do not copy the exact image. Avoid: logos, brand marks, copyrighted characters, real person likenesses, fake screenshots, UI text, readable text, watermarks, char
Two independent research teams have demonstrated working nuclear clocks based on thorium-229: one led by TU Wien in collaboration with Germany’s PTB, its national metrology institute, and another at Tsinghua University in Beijing. Their results, published in Nature on October 7, 2026, turn a long-standing goal into a functioning timekeeping concept. 4
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The central idea is to use a transition inside an atomic nucleus as a reference for measuring time. That’s different from conventional atomic clocks, which rely on transitions involving electrons. Both prototypes use thorium-229 nuclei embedded in calcium fluoride crystals. They track the frequency of light that drives a particular nuclear transition—not nuclear decay, fission or fusion. 17
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How the clocks work
In the Vienna experiment, a continuous-wave laser was stabilized to the thorium transition at 148 nanometres. Absorption spectroscopy measures how the thorium nuclei respond to the light, and rapid feedback adjusts the laser frequency to keep it aligned with the transition. 33
This makes the nuclei themselves the clock’s reference. The experiment is not simply detecting a nuclear transition: the laser is continually checked against it, so the system can use that signal for timekeeping. 33
Two teams, different milestones
The TU Wien–PTB collaboration demonstrated a self-stabilizing system that ran for more than 24 hours without intervention. Over a day of operation, its fractional frequency instability approached 10⁻¹⁵—often described as an error of roughly one second in 30 million years. That figure expresses the measurement’s precision; the clock was not tested for 30 million years. 9
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Tsinghua’s prototype was reported to have about six times greater frequency stability than the Vienna device. In separate tests, crystals grown independently produced nearly identical clock signals, agreeing to roughly three parts in 10 trillion. 19
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These results measure different things. Frequency stability describes how much a clock’s frequency fluctuates over time; agreement between separate crystals indicates how reproducible the measurements are. Neither, by itself, establishes a device’s absolute accuracy. The reported fractional frequency instability was 5 × 10⁻¹³/√(τ/s) for Tsinghua and 3 × 10⁻¹²/√(τ/s) for the PTB–TU Wien collaboration, where τ is the averaging time. 33
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A major step, not a new accuracy record
Working demonstrations from two independent teams suggest the approach is more than a one-off laboratory result. But these are still prototypes, and the published results do not show that nuclear clocks have beaten the best atomic clocks. 4
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The comparisons need careful reading: the Vienna system’s reported performance over a day and Tsinghua’s lower measured frequency instability are not interchangeable measures of absolute accuracy. So the headline that one clock is “six times better” should always specify what is being compared. 9
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What nuclear clocks could be used for
Nuclear clocks could offer a new way to test fundamental physics. The Vienna team used its clock to search for periodic variations and slow drifts in the energy of the thorium transition, using the results to constrain models of ultralight dark matter. This places limits on those models; it is not evidence that dark matter was detected. 33
Researchers also see potential for more precise timekeeping and, eventually, portable systems. For now, however, the reported achievements are prototypes—not ready-to-use technology for satellite navigation or other infrastructure. 4
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The clearest takeaway is that two independent groups have shown that a working clock can be built around a thorium-229 nuclear transition. Vienna demonstrated autonomous stabilization, while Tsinghua reported greater frequency stability and reproducible results across separately grown crystals. Those are substantial advances, but they do not yet put nuclear clocks ahead of the leading atomic clocks. 9
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On October 7, 2026, teams at TU Wien and Tsinghua University reported the first working thorium 229 nuclear clocks in Nature.
What are the key points to validate first?
On October 7, 2026, teams at TU Wien and Tsinghua University reported the first working thorium 229 nuclear clocks in Nature. The clocks use laser driven transitions inside thorium nuclei embedded in calcium fluoride crystals, rather than the electron transitions used by conventional atomic clocks.
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Vienna demonstrated more than 24 hours of self stabilizing operation; Tsinghua reported roughly six times greater frequency stability and closely matching readings from separately grown crystals.