A breakthrough in timekeeping is on the horizon as researchers at JILA, a joint initiative of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, have successfully demonstrated the components necessary to build the world’s first nuclear clock.
While atomic clocks are currently the gold standard for precision timekeeping—used to synchronize global positioning systems (GPS), the Internet, and international financial transactions—the nuclear clock is set to surpass this accuracy. By measuring time through energy transitions in an atom’s nucleus, a nuclear clock could offer even greater stability and resistance to external disturbances.
“The nuclear clock’s energy level is closely coupled to strong forces in the nucleus, whereas atomic clocks mainly depend on electromagnetic forces,” explained physicist Chuankun Zhang from JILA. “This comparison can provide sensitive tests for fundamental physics.”
Developing a nuclear clock has proven challenging, mainly because nuclear energy transitions typically require high-energy X-rays, which are beyond the capabilities of current laser technology. However, the researchers turned their attention to thorium-229, a unique isotope whose nucleus requires far less energy to induce a jump, only needing ultraviolet light instead of X-rays.
Although this phenomenon has been known since 1976, it was only this year that scientists succeeded in using ultraviolet lasers to trigger an energy jump within a thorium-229 nucleus. This advancement paved the way for the development of the first functional nuclear clock.
JILA researchers combined their previous atomic clock designs with thorium nuclei and constructed the necessary components to assemble a nuclear clock. “We managed to improve the accuracy of this measurement by a million times compared to previous measurements,” Zhang noted, marking a significant leap forward in resolving the quantum energy sublevels of this nuclear transition for the first time.
Although the team has not yet assembled the nuclear clock, they have successfully demonstrated all the required components. The focus now is on refining the accuracy of the system before it is fully operational. “We are working on improving the spectroscopy resolution further and evaluating systematic shifts of the transition,” Zhang added. “This will enable us to achieve better clock accuracy once we start operating it as a clock.”
Zhang confirmed that the technical groundwork has been laid, and building the nuclear clock could happen “any day now,” signaling that the world’s first nuclear clock is just around the corner.
In addition to offering higher precision, nuclear clocks may prove simpler to operate than current atomic clocks. “We can probe the nuclear transition in a solid-state system, which would allow us to build a much simpler clock than today’s atomic clocks,” Zhang said.