Vienna and Beijing Teams Build First Operating Nuclear Clocks

What changed

Research teams in Vienna and Beijing have independently built the first two operating nuclear clocks, using thorium-229 trapped in calcium fluoride crystals. The teams described the devices in papers published in Nature on Wednesday, calling them a step toward more precise timekeeping and a new way to study fundamental physics.

Why it matters

These are not clocks powered by nuclear fission or fusion. They keep time by measuring how a powerful laser interacts with an atom’s nucleus, shifting the action from an atom’s electrons to its much smaller core.

That matters because nuclear clocks could eventually outperform today’s best atomic clocks, first developed in 1949. For now, they do not. The achievement is therefore less about a finished replacement than about proving that this new kind of clock can operate at all.

The practical payoff remains uncertain: it is not yet clear when nuclear clocks could be deployed or how large their eventual advantage might be. Their immediate value is scientific. Researchers now have a working instrument for testing the limits of timekeeping and probing fundamental physics.