For the first time, an international team of physicists has successfully harnessed a rare orbital transition in atoms of ytterbium to create a new type of atomic clock that is both highly precise and extremely sensitive to fundamental physical effects. The researchers, led by Taiki Ishiyama at Kyoto University, say their approach could pave the way for some of the most stringent tests yet of predictions made by the Standard Model.

To measure the passing of time, an atomic clock excites an electron in confined atoms to a higher energy level, then interrogates the transition frequency of the atoms. Because these oscillations display such little variation, atomic clocks are the most accurate timekeepers ever developed.

To date, the most precise devices involve atoms trapped in an optical lattice: a periodic array of light and darkness created by interfering laser beams. These clocks operate at optical frequencies with hundreds of trillions of oscillations per second—far surpassing the microwave frequencies used in previous atomic clock designs. Already, this extraordinary precision has enabled sensitive tests of fundamental physics, as described by the Standard Model.

In 2018, theorists proposed that this sensitivity could be pushed even further using a rare type of orbital transition in ytterbium atoms. This transition occurs between configurations involving an inner-shell electron hidden deep within the atom, but can still be potentially measured and controlled with the same level of precision as conventional clock transitions. Crucially, it is also highly sensitive to the subtle effects physicists are trying to probe, including possible signatures of dark matter.

The researchers have now set stringent new constraints on such hypothetical effects under some assumptions, while also providing a valuable benchmark for theoretical models of atomic nuclei.

With some further refinements, the researchers are hopeful that this inner-shell transition could underpin a new generation of atomic clocks that not only keep time with extraordinary precision, but could also serve as powerful probes of the fundamental laws governing the universe.

Source: Nature

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