SINGAPORE, Oct 3 — Scientists in Singapore have built the world’s most accurate atomic clock, a device so precise it would take about 260 billion years to lose a single second.
Developed at the Centre for Quantum Technologies (CQT) at the National University of Singapore (NUS), the clock measures the frequency of an atomic transition to 19 decimal places, with an uncertainty of just one part in 10 quintillion.
The results, published in Nature on September 23, put the Singapore team ahead of leading atomic clocks developed in China and the United States.
The lutetium clock is about four times as accurate as the previous record holder, a calcium-ion clock developed by scientists at the Chinese Academy of Sciences in Wuhan. It also surpasses an aluminium-ion clock unveiled by the US National Institute of Standards and Technology last year.
“I am confident that what we have now is the most accurate clock in the world,” said team leader Murray Barrett, a CQT principal investigator and associate professor in the NUS Department of Physics.
Optical atomic clocks measure the highly regular frequency at which atoms switch between energy states.
The NUS clock uses a single electrically charged ion of lutetium-176, trapped while researchers tune a laser with a wavelength of 848 nanometres to match one of its atomic transitions.
Lutetium has an advantage over several other elements used in atomic clocks because its transition frequency is unusually resistant to environmental disturbances such as temperature changes and magnetic fields.
“The good properties mean that high accuracy can be achieved even in a wide range of environments,” Barrett said.
“The lutetium clock would be accurate even if you went from the hottest place recorded on Earth in Death Valley to the coldest place in the Antarctic plateau.”
To verify the result, the researchers built two lutetium clocks and compared them for more than 200 hours using correlation spectroscopy.
The pair agreed to within an uncertainty of 5.7 parts in 10¹⁹, which the researchers say is the most precise comparison yet between atomic clocks.
At that level of sensitivity, gravity itself becomes measurable.
Einstein’s theory of general relativity predicts that clocks tick more slowly in stronger gravitational fields. The lutetium clocks are sensitive enough to detect this effect across a vertical difference of just 5mm.
Such precision could eventually allow optical clocks to map subtle variations in Earth’s gravitational field and test fundamental physics.
The breakthrough comes as scientists consider replacing the caesium-based definition of the second that has underpinned international timekeeping for decades.
Optical clocks operate at much higher frequencies than conventional caesium clocks, potentially allowing time to be measured far more precisely.
The international body responsible for time standards is considering optical clocks as candidates for a redefinition of the second in or after 2030.
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.
“The next step is to take the lab-scale clock and miniaturise it into a transportable system,” said Michael Lee, a PhD student at CQT and joint first author of the study.
