Vienna team builds world's first self-stabilizing nuclear clock

Scientists in Vienna have developed the world’s first self-stabilizing nuclear clock, a device that maintains its own stability without relying on a conventional atomic clock. According to Vienna University of Technology, the prototype operated steadily for more than 24 hours without intervention. This breakthrough in metrology uses the nuclei of thorium atoms rather than electrons, offering a path toward timekeeping precision that could eventually surpass current atomic clocks.

The Role of Thorium Nuclei

The clock relies on a specific property of thorium atomic nuclei. While most atomic nuclei require enormous energy to change states, thorium has two energy states separated by an unusually small gap. This allows researchers to trigger transitions between these states using laser light.

In April 2024, 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, identified this nuclear transition experimentally. They demonstrated that laser beams could excite thorium nuclei. By autumn 2024, the team connected this apparatus to a conventional optical atomic clock, proving the nuclei could serve as a precise timekeeping reference.

Self-Stabilization Mechanism

The new device eliminates the need for an external atomic clock to maintain accuracy. The system centers on a crystal containing thorium atoms, manufactured at TU Wien, which is irradiated by a laser. The laser’s oscillation provides the rhythm for timekeeping, but environmental factors like temperature fluctuations can cause the frequency to drift.

"The oscillation of this laser light can be used for timekeeping, but the laser frequency can shift slightly from time to time, for example due to temperature fluctuations," explains Thorsten Schumm. "For high-precision measurements, you therefore need a mechanism to keep the laser frequency exactly stable, so that the clock continues to tick with precisely the same rhythm."

The thorium nuclei absorb laser light only at a precise frequency. If the laser drifts, absorption decreases. The system detects this change and automatically adjusts the laser back to the correct frequency. "What you really want is a self-stabilizing nuclear clock," says Schumm. "The basic idea is simple: you have a laser and you have thorium. The laser changes the energy state of the thorium nuclei, and the thorium nuclei are used to stabilize the frequency of the laser."

Precision and Future Improvements

The prototype achieved a relative precision of approximately 10 to the power of minus 15 over the course of a day. This corresponds to an error of roughly one second over 30 million years. While this figure is an estimate based on measurement results rather than a test lasting millions of years, it highlights the device's accuracy.

Atomic nuclei are more than 10,000 times smaller than atoms, making them less sensitive to external disturbances. "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," says Thorsten Schumm.

However, the new clock is not yet as precise as the world's leading optical atomic clocks. "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," says Schumm. Researchers aim to improve precision by using more powerful lasers and higher-quality thorium crystals.

Why it matters

This development marks a significant step in precision measurement. By using atomic nuclei as stable references, nuclear clocks could allow scientists to measure time and other physical quantities with accuracy levels that existing technologies cannot reach. More accurate timekeeping can also improve the measurement of other physical quantities, providing researchers with sensitive tools for investigating the fundamental properties of nature.

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Sources

• sciencedaily.com: Scientists build a nuclear clock that could make atomic clocks obsolete | ScienceDaily
• artsakh.news: The First Stand-Alone Nuclear Clock is Ticking in Vienna ‹ ARTSAKH NEWS
• ua.news: Self-stabilizing nuclear clock created in Vienna — ScienceDaily | UA.NEWS

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