Imagine taking just one second and dividing it into trillions of tiny moments—and then measuring those moments with extraordinary precision. That is essentially what scientists at Singapore’s Centre for Quantum Technologies (CQT) have achieved with a new atomic clock.
Researchers at CQT and the National University of Singapore have developed a lutetium-based optical atomic clock that they say has achieved the lowest measurement uncertainty ever reported for an optical atomic clock. Their results, published in Nature on September 23, 2026, could help scientists explore fundamental physics, detect tiny changes in gravity and potentially contribute to a future redefinition of the international second.
Team leader Murray Barrett, a CQT principal investigator and associate professor of physics at the National University of Singapore, said he is confident that the device is currently the world’s most accurate clock.
What makes an atomic clock so accurate?
Unlike ordinary clocks, atomic clocks do not depend on gears, springs or quartz crystals to keep time. Instead, they use the extremely stable behavior of atoms.
Atoms contain electrons that can move between different energy levels. When an electron changes its energy state, it interacts with light at a very specific frequency. This frequency is determined by the properties of the atom itself.
Scientists can use a laser to match this precise atomic transition. The oscillations of the laser light then act like an incredibly accurate pendulum.
In simple terms, the atom provides the reference, while the laser counts the ticks.
Because these atomic transitions are highly stable, scientists can use them to create clocks that are vastly more precise than conventional clocks.
From cesium to optical clocks
Atomic clocks have been used as the foundation of global timekeeping for decades. Since the 1960s, cesium atoms have defined the international standard for the second.
Cesium clocks are already extremely accurate and play an important role in technologies such as GPS, telecommunications and transportation networks.
However, scientists have discovered that other elements can provide even faster and more precise atomic transitions.
Elements including ytterbium, strontium and aluminum have become important in the development of modern optical atomic clocks. These clocks operate at much higher frequencies than traditional cesium clocks, allowing them to measure time with greater precision.
The international community is now studying measurements from these next-generation clocks as part of discussions about potentially redefining the second in 2030 or later.
Why did scientists choose lutetium?
The Singapore team began investigating lutetium more than a decade ago.
Their goal was to determine whether the element could overcome some of the environmental problems that affect extremely precise clocks.
An atomic clock does not operate in a completely isolated universe. Temperature, magnetic fields and other environmental conditions can slightly affect the frequency used for timekeeping.
Lutetium has an important advantage: its clock transition is relatively insensitive to changes in temperature and magnetic fields.
That means scientists can achieve extremely high accuracy without having to eliminate every small environmental variation.
The researchers also developed a technique called “hyperfine averaging” to help define the clock transition more precisely.
According to Barrett, these properties mean the clock could maintain its performance across a wide range of environments.
Accuracy measured to the 19th decimal place
The results are remarkable.
The researchers measured the frequency of their lutetium clock to 19 decimal places, with a reported uncertainty of just 1 × 10⁻¹⁹.
That is the lowest uncertainty reported so far for an optical atomic clock, according to the researchers.
But the team did not stop at building one clock.
They built two separate lutetium clocks and compared their ticking.
The two clocks agreed to an uncertainty of 5.7 × 10⁻¹⁹, making the comparison the most precise clock comparison reported to date.
The comparison was performed using a technique called correlation spectroscopy, with measurements collected over approximately 200 hours.
This second clock was important because scientists need more than a single device to demonstrate that an extraordinary measurement is reproducible.
As senior research scientist Kyle Arnold explained, comparing two clocks provides a way to test whether a time standard consistently produces the same result.
Each clock uses a single ion
Each of the Singapore clocks is remarkably small at its core.
The system uses a single charged lutetium-176 ion (¹⁷⁶Lu⁺). Its clock transition is controlled using a laser with a wavelength of 848 nanometers.
Despite relying on a single ion, the overall system requires sophisticated lasers, electronics, vacuum equipment and precision engineering to control and measure the ion.
The result is a clock capable of detecting differences that are almost impossible to imagine in everyday life.
The clock can detect gravity's effect on time
One of the most fascinating consequences of extreme clock accuracy is that clocks can become sensitive to gravity.
Einstein's theory of relativity tells us that gravity affects the passage of time. A clock positioned slightly higher in Earth's gravitational field can tick at a slightly different rate than one positioned lower.
With today's most advanced optical clocks, this effect is no longer merely theoretical.
The Singapore team's comparison was sensitive enough to detect the gravitational effect associated with a height difference of around 5 millimeters between the two clocks.
That means an ultra-precise clock can potentially become a tool for measuring changes in Earth's gravitational field and, indirectly, changes in height.
Why this matters beyond better timekeeping
A clock this accurate is not simply useful for knowing whether it is 10:00 or 10:01.
Scientists could use ultra-precise clocks to investigate fundamental questions in physics and search for extremely small changes that might reveal new physical effects.
They could also eventually help monitor gravitational changes across Earth.
For example, networks of highly accurate clocks could potentially detect changes related to Earth's surface and its gravitational environment. This could provide new information for geophysics and other areas of science.
The technology may also contribute to future global timekeeping standards.
As optical clocks continue to improve, researchers are gathering the evidence needed to determine whether the current definition of the second should eventually be replaced by a more precise optical standard.
The next challenge: take the clock out of the laboratory
There is still a major obstacle.
The world's most accurate optical clocks are extremely sensitive. At this level of precision, even a tiny difference in height between two clocks can affect the measurement because of gravity.
The Singapore researchers carefully measured the vertical separation of their ions to account for this effect.
Comparing their clock directly with other leading clocks around the world is also difficult because Earth's gravitational field is not currently mapped accurately enough everywhere to support comparisons at the 10⁻¹⁹ level.
The team's next goal is therefore to make the system more practical.
Researchers plan to miniaturize the laboratory-scale clock into a transportable system. This could allow the technology to be moved between locations and eventually enable new experiments and comparisons.
A new era of precision timekeeping
The development of the lutetium atomic clock represents another major step in the race to measure time with unprecedented precision.
From the cesium clocks that transformed modern timekeeping to today's optical clocks operating at extraordinary accuracy, scientists continue to push the limits of what a “second” can mean.
The Singapore team's lutetium clock demonstrates that a single atom can serve as an extraordinarily stable reference for time.
And as these clocks become smaller, more portable and even more accurate, they may do much more than tell us what time it is—they could become powerful scientific instruments for studying gravity, fundamental physics and the structure of our universe.
Reference: Arnold, K.J., Lee, M.D.K., Zhao, Q. et al. Lu+ optical frequency references with accuracy verified at the 19th digit. Nature (2026). https://doi.org/10.1038/s41586-026-11072-8
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