Synopsis: Winding up with a better clock

New measurements have pinned down the frequency of a long-lived optical transition in ytterbium with the potential for better atomic clocks.
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Today’s best timepieces are atomic clocks that rely on measurements of microwave transitions in cesium atoms, with a precision such that more than 60 million years would pass before the clock gained or lost a second. Current clock research is focused on moving to optical transitions, so that atomic clocks could be made smaller, cheaper, and even more reliable.

One route to getting to the frequency uncertainty range of 10-17 required for an optical primary time standard is to study long-lived narrow linewidth transitions in laser-cooled ions or neutral atoms. A team from the National Physical Laboratory, Oxford University, and Imperial College London in the UK report in Physical Review A their precision measurements of laser-cooled single ytterbium ions, which improve our knowledge of the key optical transition by a factor of 50.

To achieve this feat, the researchers loaded individual ytterbium ions into a trap, cooled each ion with laser beams, then pumped and probed the optical clock transition at 467 nm. By paying close attention to the accurate alignment of the lasers and ensuring high mechanical stability, Hosaka et al. were able to obtain the frequency of this extremely weak dipole-forbidden transition with an uncertainty of 2 x 10-14. The team predicts that with further improvements to the probe laser stability and temperature control, they should be able to achieve a short-term uncertainty of 10-15 and a stability of 10-17 averaged over long times. - David Voss


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