Scientists in Austria and China have developed working prototypes of what could become a new generation of ultra-precise nuclear clocks, using the nucleus of thorium-229 instead of electrons to measure time.
The two independent teams, based at the Vienna University of Technology and Tsinghua University in Beijing, described their results in separate studies published in the journal Nature this week.
Unlike conventional atomic clocks, which measure transitions between energy levels of electrons, nuclear clocks use a laser tuned to a transition between energy states inside an atomic nucleus.
How nuclear clocks work
Atomic clocks already provide extremely precise timekeeping and underpin technologies including GPS and telecommunications.
In a conventional atomic clock, a laser is tuned to a precise frequency associated with an electron moving between energy levels. A nuclear clock instead targets changes within the much smaller atomic nucleus.
The teams are using thorium-229 because its nucleus has an unusually low-energy transition that can be reached with a laser, making it suitable for the technology.
“The basic idea is simple: you have a laser and you have thorium,” said Thorsten Schumm, a study co-author and professor at the Vienna University of Technology.
The laser changes the energy state of thorium nuclei, while the nuclei help stabilise the laser’s frequency.
Nuclear clocks are not yet more accurate
Despite their potential, the prototypes are still behind existing atomic clocks in precision.
Researchers estimate that the current nuclear clock prototypes could drift by about one second every 30 million years. That is roughly 10 times less accurate than the cesium clocks used to define the official second.
Testing has reportedly found that the Chinese prototype is about six times more stable than the Austrian version. The Vienna team, however, developed what researchers describe as the first nuclear clock to stabilise itself using a method similar to that used by atomic clocks.
Could help study dark matter
Scientists believe improvements to the technology could eventually make nuclear clocks significantly more accurate.
Stronger lasers and improved thorium crystals could help researchers reduce measurement uncertainties and potentially push nuclear clocks beyond the capabilities of current atomic clocks.
Such precision could have applications beyond timekeeping. Researchers believe future nuclear clocks could be sensitive enough to investigate subtle physical effects and potentially help scientists search for phenomena such as dark matter.
For now, the competing teams are still working to improve the technology, with the race to build a nuclear clock that can outperform atomic clocks still open.
