A team led by physicist Thorsten Schumm at the Vienna University of Technology (TU Wien) says it has built the first working clock that uses the high-frequency oscillations of atomic nuclei to measure time — rather than those of electrons, as has been standard until now. The system ran for 24 hours without external intervention. Schumm called the development the "culmination of 15 to 20 years of research."
For this so-called nuclear clock, the researchers embedded the element thorium-229 in a crystal of calcium fluoride and excited it with an ultraviolet laser. Because transitions between the energy states of an atomic nucleus are more energetic and oscillate at a higher frequency than those in the electron shell, such a clock could measure time even more precisely. Another advantage: the nucleus is largely shielded from its surroundings, and the clock works at room temperature, without elaborate cooling close to absolute zero.
From concept to a running clock
The idea dates back to 2003, when physicist Ekkehard Peik of Germany's national metrology institute (PTB) in Braunschweig helped develop the principle. In late 2023, his group showed that an atomic nucleus can be deliberately excited with laser pulses. The key to a real clock was a mechanism to regulate the frequency: the laser continuously alternates between two frequencies just above and just below the nuclear resonance and automatically corrects itself based on the measured absorption.
The nuclear clock does not yet match the stability of today's best atomic clocks, such as those at the PTB. The study has so far appeared only as a preprint on the "arXiv" server and has not yet been independently reviewed. The team explicitly describes it as a proof of concept and is confident of achieving significantly better results with more powerful lasers. If successful, it could enable more precise navigation, more stable networks and more secure digital communication — and allow physicists to measure fundamental constants of nature more accurately.