Timekeeping at the 19th digit
A team at the Centre for Quantum Technologies at the National University of Singapore has built what it says is the most accurate atomic clock yet. The device uses a single lutetium ion and measures the vibration of the atom to 19 decimal places. The researchers reported an uncertainty of about 1 x 10⁻¹⁹, the lowest recorded for an optical atomic clock. The work was published in Nature on September 23.
Optical clocks work by counting the light an atom absorbs when it changes energy state. The steadier that frequency, the better the clock. The lutetium transition is unusually insensitive to temperature and magnetic fields, which helps.
Two clocks, one answer
To test the design, the team built two clocks and let them run side by side for 200 hours. The pair agreed to within 5.7 x 10⁻¹⁹. According to the researchers, that is the most precise comparison of two clocks ever reported.
The team also invented a technique it calls hyperfine averaging to define the clock transition, and measured the height of the ions to under a millimetre. Small differences in height matter because gravity changes the pace of time.
Why it matters
A more accurate clock could help physicists test whether the constants of nature change over time, and could support new ways to define the second. The current definition is based on caesium, which ticks at microwave frequencies. Optical clocks run hundreds of thousands of times faster, which makes them harder to build but far more precise.
The result is a 41 per cent improvement over the previous record holder, the team says. Others in the field caution that record claims depend on how uncertainty is measured, and that it takes years to move such designs out of the laboratory. Even so, the comparison between two independent clocks gives the measurement unusual weight. The researchers now plan further runs to reduce the uncertainty.