"A Clock in Singapore Just Became the Most Accurate Timekeeper Ever Built"

The standard for measuring time has been the same for nearly six decades: an atom of caesium, ticked by a microwave tuned so that exactly 9,192,631,770 cycles pass for every official second. Now a team in Singapore has built something better — an atomic clock that measures time so precisely it would drift by no more than a second over roughly 300 billion years, about twenty times the age of the universe. The result, published in Nature on September 23, comes from the Centre for Quantum Technologies (CQT) at the National University of Singapore.

The clock is built around a single ion of lutetium — element 71, a rare-earth metal most people have never heard of. "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 NUS's Department of Physics. The claim rests on a number: the team measured the frequency of their clock transition to 19 decimal places, reporting an uncertainty of 1 × 10⁻¹⁹, the lowest ever recorded for an optical atomic clock.

To understand why that matters, it helps to know how these clocks work. Every atomic clock keeps time against a fixed "clock transition" — the moment one of an atom's electrons jumps between energy levels. A laser is locked to that transition, and its light oscillations act like the swings of a pendulum. Caesium has held the global standard since the 1960s, quietly underpinning GPS, telecommunications, and financial networks. But caesium oscillates relatively slowly; elements like ytterbium, strontium, and aluminium tick far faster, which lets them keep time more accurately.

Lutetium was a deliberate bet. The CQT group began working with it more than a decade ago on the hunch that it had the right properties, and they remain, to their knowledge, the only group using it for timekeeping. The payoff is that lutetium's clock transition barely responds to changes in temperature or magnetic field — the two environmental factors that normally nudge a clock's frequency out of tune. The team even had to invent a scheme they call "hyperfine averaging" to define the transition in the first place. Barrett puts the practical consequence plainly: the clock would stay stable "from the hottest place recorded on Earth in Death Valley to the coldest place in the Antarctic plateau."

There's a deeper lesson in how they proved it. The team didn't build one clock; they built two and compared their ticking over 200 hours using a technique called correlation spectroscopy. The clocks agreed to within 5.7 × 10⁻¹⁹ — the most precise clock comparison ever made. Senior Research Scientist Kyle Arnold, a joint first author on the paper, reaches for a classic joke to explain why: "A man with a watch knows what time it is. A man with two watches is never sure." The only way to test a standard is to compare it against another and show the results reproduce. Accuracy, in other words, is only as credible as the comparison that backs it.

That comparison revealed something remarkable: at this level of precision, gravity itself becomes the limiting factor. Clocks this accurate can feel the slowing of time caused by a height difference of mere millimetres. The CQT setup could resolve a five-millimetre difference in height between two clocks sitting on the same table. This is one of the more striking twists of the result — the thing that would eventually stop a better clock from being built isn't the physics of the atom, but the fact that we don't yet know the shape of Earth's gravitational field well enough to compare clocks across distant laboratories.

That limitation points to the technology's second life. A clock sensitive enough to feel millimetres of altitude is no longer just a timekeeper; it's a gravity sensor. This is the field of relativistic geodesy, and it has practical ambitions: mapping groundwater, tracking ice-sheet loss, and monitoring the slow shifts of volcanic and tectonic systems by detecting tiny changes in local gravity. The same precision that keeps time can measure the planet.

The near-term engineering goal is more modest but just as consequential. PhD student Michael Lee, the paper's other joint first author, says the next step is to shrink the lab-scale clock into a transportable system without compromising accuracy. That matters because redefining the second — something the international metrology community is weighing for 2030 or later — will require moving these clocks around and comparing them across continents. A clock that can't travel can't help set the world's standard.

Lutetium's entry lands in an already crowded race. Strontium-based optical lattice clocks have set records for years, and a Japanese firm recently commercialized one. Meanwhile, researchers are working toward nuclear clocks built on a thorium transition that could someday leapfrog the optical clocks entirely. Singapore's contribution isn't just a new number on the leaderboard; it's a demonstration that the material you choose for the clock is itself a design frontier — find an atom whose transition is naturally immune to noise, and precision follows.

For the rest of us, the immediate payoff is invisible. The caesium clocks we already depend on are staggeringly good; the improvements being made now won't change what your phone's clock says. But they do change what those clocks enable downstream — more resilient GPS, tighter synchronization for networks and markets, and measurement tools for science we can't yet do. Precision at the frontier has a way of quietly becoming infrastructure.

What's most impressive about this result isn't the headline number, though the headline number is genuinely astonishing. It's that it took a decade of methodical work on an obscure element, an invented averaging scheme, and a careful two-clock comparison to get there. The most accurate clock ever built wasn't a flash of insight. It was patience — the same patience, you might say, that a clock exists to measure.

Further reading: the NUS announcement and the CQT highlight detail the work, IEEE Spectrum covers the first commercial optical clock, and Popular Science explains where nuclear clocks may take timekeeping next.