Insider Brief
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Researchers at Singapore’s Centre for Quantum Technologies reported a lutetium-ion atomic clock that would be off by no more than about one second over 300 billion years, achieving the best reported accuracy for an optical atomic clock.
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The team compared two single-ion lutetium clocks over 200 hours, finding their ticks matched closely enough to differ by about one second over 55 billion years, marking the most precise clock comparison reported to date.
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The clocks’ low sensitivity to temperature and magnetic fields could aid studies of gravity and fundamental physics, contributing data toward a possible redefinition of the second after 2030.
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In the lab at the Centre for Quantum Technologies, researchers (from left) Associate Professor Murray Barrett, PhD student Michael Lee, and Senior Research Scientist Kyle Arnold are actively working on this advancement.
PRESS RELEASE — Take a second and turn it into trillions of moments. Measure each one. That’s how precisely an atomic clock at Singapore’s Centre for Quantum Technologies (CQT) keeps time – and with record-making accuracy, according to results published in Nature on 23 September.
“I am confident that what we have now is the most accurate clock in the world,” says team leader Murray Barrett, a CQT Principal Investigator and Associate Professor in the Department of Physics at the National University of Singapore.
The researchers’ claim is supported by measurements showing that their atomic clock, built from lutetium, outperforms previous record holders made from other elements. More accurate clocks could explore unknowns in fundamental physics and monitor gravitational changes on Earth while vying to redefine the second.
Pushing the Limits of Timekeeping
Atomic clocks keep time by referencing an atomic transition when an atom’s electron swaps energy levels. The frequency of this transition is a fixed property of the atom, and a laser matched to this ‘clock transition’ counts time.
This established method has been in use for decades, with cesium atoms setting the global time standard since the 1960s. Cesium atomic clocks now support GPS and synchronize communication networks.
However, scientists are continually pushing the limits of timekeeping with alternative elements.
Recent record-holders like ytterbium, strontium, and aluminum oscillate much faster than cesium, leading to greater timekeeping accuracy. The international body responsible for time standards is considering data from new optical atomic clocks for a redefinition of the second, expected in or after 2030.
The CQT team has been working with lutetium for over a decade, believing it has the right properties for superior performance. They are currently the only group using this element for timekeeping.
The team measured the frequency of their lutetium clock to 19 decimal places, achieving an uncertainty of (1 \times 10^{-19}), the lowest reported for any optical atomic clock. Additionally, their clock comparison exhibited an uncertainty of (5.7 \times 10^{-19}), indicating the most precise clock comparison to date. Future measurements may further reduce this uncertainty.
Lutetium’s Advantage
Lutetium performs well, as its clock transition is minimally affected by changes in temperature or magnetic fields—factors that can alter the frequency of transitions in other elements.
“Given its properties, I believe this clock is hard to beat,” states Associate Professor Barrett. His team has invested over ten years refining their atomic clock setup and developing a method called ‘hyperfine averaging’ to clearly define the clock transition.
“The excellent properties mean high accuracy can be maintained across various environments,” Barrett adds. “The lutetium clock would remain stable from the hottest regions like Death Valley to the coldest areas in Antarctica.”
Two is Better Than One
The team’s confidence is reinforced by their comparison of clocks, employing correlation spectroscopy over 200 hours. Each lutetium clock consists of a single charged (^{176})Lu(^+) ion, with a clock transition aligned to a laser wavelength of 848 nanometers.
“One saying is that ‘a man with a watch knows what time it is; a man with two watches is never sure,’” says Kyle Arnold, a Senior Research Scientist from CQT and joint first author on the paper. “It emphasizes that the only way to test a standard’s accuracy is by comparing clocks and proving reproducibility.”
The team also aims to compare their lutetium clock with other top atomic clocks, but this poses challenges. Optical atomic clocks at the (10^{-19}) level are so accurate that they can detect gravity’s effects over millimeter height differences. This clock comparison can resolve a 5mm height difference between clocks; however, gravity differences on Earth are not accurately known enough for comparison at this precision level.
For new comparisons and exploring applications, the clock should transition out of the lab. “The next step is to miniaturize the lab-scale clock into a transportable system,” states Michael Lee, joint first author on the paper and PhD student. The researchers believe they can reduce the clock’s size without sacrificing accuracy.
