A new clock has successfully measured time for more than 24 hours using atomic nuclei.
To measure time, a clock needs a regular rhythm. An old pendulum clock counts the movements of its pendulum. An electronic watch uses the vibrations of a small crystal. Atomic clocks, which are much more precise, make use of atoms.
In a traditional atomic clock, electrons are used—tiny particles that surround the atom's nucleus. When they receive waves at a very precise frequency, they change state. The device uses this frequency as a reference to count the seconds.
The new clock works on a similar idea, but with one important difference: it uses the nucleus, at the center of the atom, rather than the electrons around it. This nucleus is generally better protected from external disturbances. It could therefore make it possible to measure time with even greater regularity.
The problem is that it is very difficult to make a nucleus react to light. A rare element, thorium-229, nevertheless has a special property: its nucleus can change state when it receives a very specific ultraviolet light.
Researchers from TU Wien placed thorium in a small crystal and then illuminated it with a laser. When the laser emits at the right frequency, the nuclei absorb some of the light. If this frequency changes, the absorption changes as well. The device detects this and automatically adjusts the laser to maintain the correct rhythm.
This system worked for more than 24 hours without intervention. The measured regularity would correspond, by comparison, to an error of about one second over 30 million years.
Even so, it does not yet outperform today's best atomic clocks. What is new is that researchers have succeeded in automatically maintaining a laser's rhythm using atomic nuclei. They hope to improve its precision in the coming years.
Such a clock could also help study mysteries in physics. By comparing its rhythm with that of an atomic clock, scientists can search for tiny changes that could, for example, be linked to dark matter. So far, the first tests have revealed no signal of this kind.