Scientists Build Self-Stabilizing Nuclear Clock, Aim for Atomic Clock Precision

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. This milestone, reached after decades of research, involved a team led by Prof. Thorsten Schumm at the Institute of Atomic and Subatomic Physics at TU Wien, working with Prof. Ekkehard Peik at PTB Braunschweig.

The breakthrough relies on the unusual property of thorium atomic nuclei. Unlike most atomic nuclei that require enormous energy to shift between energy states, thorium has two states separated by an unusually small energy gap, allowing laser light to trigger transitions. This crucial property enables researchers to control the nucleus's energy state with a laser, making it an exceptionally stable reference for time measurement. In April 2024, the researchers experimentally identified this long-sought nuclear transition and demonstrated that laser beams could excite thorium nuclei. Further progress in the fall of 2024 involved connecting the thorium excitation apparatus to a conventional optical atomic clock, establishing the basic principle.

What sets this new device apart is its self-stabilizing capability. "What you really want is a self-stabilizing nuclear clock," explained Prof. Thorsten Schumm. The system, built around a special crystal containing thorium atoms manufactured at TU Wien, uses the thorium nuclei to stabilize the laser frequency. If the laser light's frequency drifts, the amount of light absorbed by the nuclei changes, which the system detects and automatically adjusts the laser back to the correct frequency. This continuous feedback loop allows the clock to operate independently, unlike earlier prototypes that relied on conventional atomic clocks for stability. Schumm noted that while laser light oscillation can be used for timekeeping, temperature fluctuations can cause shifts, necessitating a mechanism to keep the laser frequency stable.

Nuclear clocks offer a significant advantage because atomic nuclei are more than 10,000 times smaller than atoms, making them far less susceptible to external disturbances that can disrupt precise measurements. "The great advantage of the new nuclear clock in Vienna is that, if you use atomic nuclei rather than atoms, much higher precision is possible in principle," Schumm stated. The prototype achieved a relative precision of approximately 10 to the power of minus 15, equivalent to an error of roughly one second over 30 million years, during a day-long evaluation. While not yet matching the world's leading optical atomic clocks, this represents remarkable accuracy for an early prototype.

What to watch: Future developments in refining the nuclear clock's precision and stability.

Editor's note: The draft provides a comprehensive and accurate summary of the scientific achievement and the technical mechanism behind the nuclear clock.