Physicists Build the Most Accurate Atomic Clock Ever

Take a second and imagine splitting it into trillions of tiny moments, then measuring each one with near-perfect precision. That is essentially what a team of physicists in Singapore just managed to do, and in the process, they may have found the element that eventually redefines the second itself.

A Decade of Betting on One Element

Researchers at the Centre for Quantum Technologies (CQT) at the National University of Singapore built the new clock using the rare-earth metal lutetium, specifically a single charged lutetium-176 ion. The team, led by Associate Professor Murray Barrett, started working with this element more than a decade ago on a hunch that it had the right atomic properties to compete with the field’s top performers. As far as the team knows, they remain the only group in the world working with lutetium for timekeeping. Their results, published in Nature on September 23, suggest that bet has paid off. “I am confident that what we have now is the most accurate clock in the world,” Barrett said.

From Cesium to the 19th Digit

Atomic clocks work by locking a laser to the precise frequency of an atomic transition, the moment an atom’s electron jumps between energy levels, and using the resulting light oscillations to count time the way a pendulum would. Cesium atoms have anchored the global definition of a second since the 1960s and still underpin GPS and telecommunications networks today. More recently, researchers have pushed accuracy further using elements like ytterbium, strontium, and aluminum, which oscillate faster than cesium and keep time more precisely. The international body responsible for timekeeping standards is weighing data from these newer optical atomic clocks as it considers redefining the second, likely in or after 2030. The CQT team measured their lutetium clock’s frequency to 19 decimal places, reporting an uncertainty of just 1 in 10 quintillion, the lowest ever reported for any optical atomic clock, a roughly 41 percent improvement over the previous record holder, which was built using calcium ions.

An Endurance Athlete Among Atoms

What sets lutetium apart is how little its clock transition reacts to the messy conditions of the real world. Study co-author Murray Barrett compared the challenge of precise timekeeping to an ultramarathon, describing the clock’s core isotope as the runner that has to go the distance, and calling lutetium a natural born endurance athlete. In other elements, shifts in temperature, magnetic fields, and gravity can subtly alter the frequency of the clock transition, introducing error. Lutetium’s atomic structure makes it far less sensitive to these effects: while other optical clocks may need their surroundings controlled to within a few thousandths of a degree, the lutetium clock keeps ticking accurately through a 5-degree external temperature swing. Barrett said the clock would remain stable even moving between the hottest recorded place on Earth, Death Valley, and the coldest, the Antarctic plateau. The team also developed a technique called hyperfine averaging specifically to dull the effects of gravitational fields on the clock transition.

Why Two Clocks Beat One

Claiming a record for accuracy requires more than a single measurement. As Kyle Arnold, a CQT senior research scientist and joint first author on the paper, put it, quoting an old joke: a man with one watch knows what time it is, but a man with two watches is never sure, meaning the only real way to test a clock’s accuracy is to compare it against another and check that the results match. The team built two separate lutetium clocks and compared their ticking over 200 hours using a technique called correlation spectroscopy. The two clocks agreed to an uncertainty of 5.7 in 10 quintillion, which the researchers describe as the most precise clock comparison ever performed. At that level of precision, the clocks could detect gravitational time dilation from a height difference of just 5 millimeters between them sitting on the same table, a effect the team had to independently measure and account for to keep it from limiting their results.

Where the Clock Goes From Here

Beyond its potential role in redefining the second, a sufficiently precise atomic clock could help physicists probe some genuinely fundamental questions, including whether constants like the gravitational constant G are truly constant over time or subtly changing, something Barrett says remains a subject of real speculation in the field. Michael Lee, a PhD student and the paper’s other joint first author, said the next major goal is to shrink the lab-scale clock down into a transportable system without sacrificing its accuracy. A smaller, portable version could eventually allow direct comparisons with the world’s other leading atomic clocks and open the door to practical applications well beyond the laboratory, including precise geodesy, monitoring gravitational changes across Earth’s surface, and fundamental physics research that today remains out of reach.

Sources

This report draws on the National University of Singapore’s own announcement, with additional coverage from Live Science, of the peer-reviewed study by Arnold, Lee, Zhao, Qin, Zhang, Jayjong, and Barrett, published in Nature (2026).