Scientists build a nuclear clock that could make atomic clocks obsolete

Researchers in Vienna have built the world’s first self-stabilizing nuclear clock, bringing scientists closer to a new era of ultra-precise timekeeping.

Scientists have reached a major milestone in the quest to build an entirely new kind of clock. After decades of research, a team in Vienna has developed the world's first self-stabilizing nuclear clock, a device that could eventually measure time with far greater precision than today's most advanced atomic clocks.

Unlike earlier prototypes, the new nuclear clock can maintain its own stability without depending on a conventional atomic clock. Researchers have demonstrated that it can operate steadily for more than 24 hours without intervention.

The achievement represents an important advance in precision measurement, also known as metrology. By using atomic nuclei as exceptionally stable references, nuclear clocks could eventually allow scientists to measure time and other physical quantities with levels of accuracy that existing technologies cannot reach.

The breakthrough relies on an unusual property of thorium atomic nuclei that scientists have investigated for decades.

Atomic nuclei can exist in different energy states, but moving between those states typically requires enormous amounts of energy. Thorium is a rare exception. Two of its nuclear energy states are separated by an unusually small energy gap, making it possible to trigger a transition between them using laser light.

This property is crucial because it allows researchers to control the energy state of a nucleus with a laser, something that is not possible in the same way for most other atomic nuclei. Scientists can then use this extremely precise transition as a reference for measuring time.

A major breakthrough came in April 2024, when researchers led by Prof. Thorsten Schumm at the Institute of Atomic and Subatomic Physics at TU Wien, working with a team led by Prof. Ekkehard Peik at PTB Braunschweig, identified the long-sought nuclear transition experimentally. They demonstrated for the first time that laser beams could excite thorium nuclei.

Further progress followed in the fall of 2024. The researchers connected their thorium excitation apparatus to a conventional optical atomic clock, demonstrating that the nuclei could serve as a highly precise timekeeping reference.

Although this established the basic principle of a nuclear clock, one essential capability was still missing: the ability to maintain its own accuracy independently.

"What you really want is a self-stabilizing nuclear clock," explains Prof. Thorsten 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."

To make this possible, the researchers developed a system built around a special crystal containing thorium atoms, manufactured at TU Wien. A laser shines onto the crystal, interacting with the thorium nuclei inside.