The first nuclear clock could change the rules of metrology

September 4 () –

Physicists have managed to combine a high-precision optical atomic clock with a high-energy laser system and have successfully coupled it to a crystal containing atomic nuclei of thorium.

Thorium atomic nuclei can now be used as a time-measuring device, making the clock even more precise: it is the world’s first nuclear clock, as is presented in the journal ‘Nature’.

It does not yet offer greater precision than a conventional atomic clock, but that was not the aim of this first step. “With this first prototype we have demonstrated that thorium It can be used as a stopwatch for very high precision measurements.. Now all that remains is to carry out technical development work, so no major obstacles are expected,” he says. in a statement Professor Thorsten Schumm of the Vienna University of Technology and lead author of the study.

The atomic clock at JILA – a research institute of the National Institute of Standards & Technology (NIST) and the University of Boulder, USA – has been successfully coupled to thorium atomic nuclei. This required some physical tricks: “The atomic clock works with laser light in the infrared range, which is used to excite the strontium atoms. However, our thorium atomic nuclei need radiation in the ultraviolet range,” explains Thorsten Schumm. “Therefore, We need a way to convert infrared frequencies into ultraviolet frequencies.similar to a mechanical transmission that converts a slow rotation frequency into a faster rotation by means of suitable gears.”

For this purpose, ultrashort infrared laser pulses consisting of a series of different infrared frequencies were used. The distance between two neighbouring frequencies is always the same, like the distance between the teeth of a comb, which is why it is also called a “frequency comb”. This frequency comb of infrared light hits a xenon gas, and the xenon atoms They react to infrared light by producing ultraviolet light in a very predictable and precise manner.

This UV light is then directed at a tiny crystal containing thorium nuclei. “This crystal is the core element of the experiment,” explains Thorsten Schumm. “It was manufactured at the Technical University of Vienna and several years of development work were needed to develop the necessary knowledge.”

The combination of these elements has worked well and the result is the world’s first nuclear clock. This first prototype does not yet offer an increase in precision, but that was never intended.Our goal was to develop a new technology. Once it is there, the increase in quality occurs naturally, that has always been the case,” Thorsten Schumm says: “The first cars were not faster than carriages. It was about introducing a new concept. And that is exactly what we have now achieved with the nuclear clock.”

This has also made it possible to measure the energy of the thorium states with extreme precision, orders of magnitude higher than previously possible. “When we first excited the transition, we were able to determine the frequency with an accuracy of a few gigahertz, which was already more than a thousand times better than anything known before. However, we now have an accuracy in the kilohertz range, which is in turn a million times better,” emphasises Thorsten Schumm. “In this way, we hope to surpass the best atomic clocks in two or three years.”

Not only will this technology allow time measurements to be made much more accurately than previous clocks, but it will also make it possible to measure other physical quantities more accurately in the future. Thorium technology could bring about significant advances in many fields of research, from geology to astrophysics. This extreme precision could now be used, for example, to study the fundamental laws of nature and to investigate whether the constants of nature may not be entirely constant. but may change over space and time.