Elusive ‘nuclear clocks’ tick closer to reality — after decades in the making

Researchers are attempting to build the world’s first nuclear clock. This is a view inside the vacuum chamber that holds crystals doped with the isotope thorium-229, which can be excited by a laser.Credit: Ye Labs/JILA/NIST/University of Colorado

Denver, Colorado

Physicists are getting closer to creating a long-sought ‘nuclear clock’. This device would keep time by measuring energy transitions in the nuclei of atoms and could become the most precise clock on the planet.

Decades ago, scientists predicted that the isotope thorium-229 could be used in such a clock, but they couldn’t pin down its unusual nuclear energy transition. That feat, achieved with a laser in 2024, started the countdown to a nuclear clock.

‘Nuclear clock’ breakthrough paves the way for super-precise timekeeping

Now, such a clock is “way closer than people think”, says Eric Hudson, a physicist at the University of California, Los Angeles, who is working on one. “You’ll see nuclear-clock measurements in 2026, I’m sure.”

Nearly a dozen research teams spread across China, Europe, Japan and the United States are closing in on assembling the components of such a clock, including a source of thorium-229 — which is radioactive — and a powerful continuous-wave ultraviolet laser to excite the energy transition. At the American Physical Society (APS) Global Physics Summit in Denver, Colorado, this week, researchers provided updates on their progress, including details of laser development.

Claire Cramer, the executive director of quantum science at the University of California, Berkeley, who was in attendance, expressed optimism about the potential of solid-state nuclear clocks: “This is a really, really promising technology for commercial applications.”

That’s because nuclear clocks could be resilient to noise and have a compact design for use outside the laboratory. They might also surpass the precision of optical atomic clocks, the field’s current top timekeepers, which lose only one second every 40 billion years.

Laser jockeying

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