In a first, scientists have used a tabletop laser to bump an atomic nucleus into a higher energy state. It’s a feat that sets scientists on a path toward creating the first nuclear clock, which would keep time based on the inner workings of atomic nuclei.
Compared to atomic clocks — currently scientists’ most precise timekeepers — nuclear clocks could be simpler and more portable. And they could be used to test fundamental physics theories in new ways. With the new result, a nuclear clock seems more attainable than ever: “We know now that it’s conceptually feasible,” says physicist Peter Thirolf of Ludwig-Maximilians-Universität München in Germany, who was not part of the study.
Nuclear clocks would use the transitions of atomic nuclei, rather than electrons, to mark time. While most atomic nuclei have energy levels too far apart for a laser to kick off the jump, one special nucleus is an outlier. A variety of the element thorium, thorium-229, has an unusually small energy jump, accessible to lasers.That allowed physicists to take the next step.
In the experiment, the thorium-229 was embedded in a crystal of calcium fluoride. This differs from atomic clocks, in which atoms are contained in a vacuum chamber. The possibility of making future nuclear clocks out of solid materials is part of their appeal: “Potentially you could imagine building a much simpler, portable system, taking this clock out of the lab,” says physicist Jun Ye of JILA in Boulder, Colo., who was not involved with the new research.