Scientists build a nuclear clock that could make atomic clocks obsolete
Scientists in Vienna have achieved a major breakthrough in timekeeping by creating the world’s first self-stabilizing nuclear clock, a technology that could eventually surpass even the most precise atomic clocks. Instead of relying on electrons in atoms, the clock uses the tiny nuclei of thorium atoms, which are far less sensitive to outside disturbances.
Key points
- A team in Vienna has built the world's first self-stabilizing nuclear clock.
- The clock ran steadily for more than 24 hours without a conventional atomic clock.
- Its measured precision is about 10 to the power of minus 15, or one second over 30 million years.
Scientists in Vienna have developed the world's first self-stabilizing nuclear clock, a device that could eventually measure time more precisely than today's most advanced atomic clocks. The team, led by Prof. Thorsten Schumm at TU Wien with Prof. Ekkehard Peik's group at PTB Braunschweig, reported the milestone after decades of research.
Unlike earlier prototypes, the new clock maintains its own stability without relying on a conventional atomic clock. It operated steadily for more than 24 hours, according to the researchers.
How the clock works
The breakthrough uses an unusual property of thorium atomic nuclei. Two of thorium's nuclear energy states are separated by an unusually small energy gap, allowing laser light to trigger a transition between them. In April 2024, the researchers identified this long-sought transition experimentally and showed that laser beams could excite thorium nuclei. In fall 2024, they connected their thorium apparatus to a conventional optical atomic clock, demonstrating that the nuclei could serve as a precise timekeeping reference.
The self-stabilizing system centers on a special thorium-containing crystal made at TU Wien. A laser shines onto the crystal, and the thorium nuclei absorb light only at precisely the correct frequency. If the laser drifts, absorption drops, and the system automatically adjusts the laser back to the right frequency. This continuous feedback keeps the clock ticking at a consistent rate without a conventional atomic clock.
This is not yet at the level of the world's best optical atomic clocks, but for a first prototype it is a fantastic result.
— Thorsten Schumm
Precision and next steps
Over one day, the prototype achieved a relative precision of about 10 to the power of minus 15, equivalent to an error of roughly one second over 30 million years. That figure describes measured precision, not an actual test lasting millions of years. The clock is not yet as precise as the world's best optical atomic clocks.
The researchers plan to improve precision with more powerful lasers and higher-quality thorium crystals. They say such upgrades could eventually let nuclear clocks outperform existing atomic clocks and improve measurement of other physical quantities.
