Scientists at the National University of Singapore have built a lutetium atomic clock that measures transition frequency to 19 decimal places with an uncertainty of one part in 10 quintillion. The device, developed at the Centre for Quantum Technologies and published in Nature on September 23, takes 260 billion years to lose a single second. The researchers stated this is the lowest uncertainty recorded so far for any optical atomic clock, creating a world record that leaves behind the US and China.
National University of Singapore Builds Lutetium Clock
The team also created a “hyperfine averaging” method to define the clock transition and believe they are the only group using lutetium for timekeeping. Lutetium resists environmental disturbances like temperature swings and magnetic fields better than other elements, allowing it to maintain high accuracy even when moving between extreme environments like Death Valley and the Antarctic plateau, according to team leader Murray Barrett, a principal investigator at the Centre for Quantum Technologies and associate professor in the National University of Singapore Department of Physics. Barrett said, “I am confident that what we have now is the most accurate clock in the world.”
The device achieves four times the precision of the previous record holder, a calcium-ion clock built by the Chinese Academy of Sciences in Wuhan, and surpasses an aluminium-ion clock unveiled by the U.S. National Institute of Standards and Technology last year. It also outperforms clocks using strontium and ytterbium. David Leibrandt, a physicist at the University of California, Los Angeles who works on ultra-precise clocks, described the device’s accuracy as impressive.
Lutetium clocks detect gravitational time dilation
The pair agreed to within an uncertainty of 5.7 parts in 10¹⁹, which is the most precise comparison yet between atomic clocks. Regarding the need for two devices, Barrett said, “It basically tells you that the only way to test the accuracy of a standard is to compare clocks and demonstrate reproducibility.”
At that level of sensitivity, Einstein’s theory of general relativity predicts that clocks tick more slowly in stronger gravitational fields. The lutetium clocks detect this gravitational time dilation across vertical height differences of just 5 millimetres. To achieve this, researchers ensured the vertical separation between the two ions was better than one millimetre.
Optical clocks provide more accurate measurements than caesium
Caesium-based atomic clocks have underpinned international timekeeping and supported GPS, communications, and transport networks since the 1960s, but optical clocks operate at much higher frequencies to measure time more precisely. Because they have more oscillations to count over the same interval, they offer more accurate measurements.
For now, the lutetium clock remains a laboratory-scale experiment. The Singapore team’s next goal is to shrink it into a transportable system for field measurements of gravity and tests of fundamental physics, according to Michael Lee, a PhD student at the Centre for Quantum Technologies and joint first author of the study. Barrett added, “In the future, I just don’t see how this clock can be beat.”
Frequently Asked Questions About the Lutetium Atomic Clock
Why was lutetium chosen over caesium for this atomic clock?
Lutetium’s transition frequency is unusually resistant to temperature changes and magnetic fields, making it stable across extreme environments. While caesium atomic clocks have defined the second since the 1960s, optical clocks using elements like lutetium operate at much higher frequencies.
How much more accurate is the new Singapore clock than previous models?
The lutetium clock is about four times as accurate as the previous record holder, a calcium-ion clock developed by the Chinese Academy of Sciences in Wuhan, and surpasses the aluminium-ion clock built by the U.S. National Institute of Standards and Technology.
When might the international definition of the second change?
The international body responsible for time standards is considering optical clocks as candidates for a redefinition of the second in or after 2030.