A clock that would lose one second only after about 260 billion years now exists in a laboratory in Singapore. That is nearly 20 times the age of the universe, as the South China Morning Post pointed out.
Researchers at the Centre for Quantum Technologies (CQT) at the National University of Singapore built it. The team reported the results in the journal Nature on 23 September, according to Malay Mail and Live Science.
One ion, one laser
The clock is built around a single electrically charged atom, a lutetium-176 ion. The ion is held in a trap, and researchers tune a laser with a wavelength of 848 nanometres to match one of its atomic transitions. The laser’s steady oscillation is what “ticks”.
Malay Mail reports that the clock measures this transition frequency to 19 decimal places, with an uncertainty of about one part in 10 quintillion.
Optical atomic clocks usually rely on elements such as strontium, ytterbium or aluminium. Using lutetium is unusual. The SCMP reports that the Singapore group says it is probably the only one in the world building clocks with it.
Why lutetium
The team says the element’s transition is unusually resistant to outside disturbance. Temperature and magnetic fields barely shift it. That matters because those effects are among the main sources of error in precision clocks.
Murray Barrett, a principal investigator at CQT and associate professor at NUS, gave an example in a press release. He said the clock would stay accurate even if it were moved from Death Valley, the hottest place recorded on Earth, to the Antarctic plateau.
The SCMP adds another advantage. Lutetium can stay in an excited state for about a week, compared with a few minutes for strontium. A longer-lived state is useful for making very fine measurements.
Barrett used a running analogy with Live Science. He said the job is to make sure the “runner” can go the distance, and that lutetium is a natural endurance athlete.
Checking the result
A claim of record accuracy needs a check. According to Malay Mail, the team built two lutetium clocks and compared them for more than 200 hours using a technique called correlation spectroscopy. The two agreed to within 5.7 parts in 1019. The researchers say this is the most precise comparison yet between two clocks.
Interesting Engineering reports that the team also had to invent a new way to define the clock’s transition. A project lead said the group spent much of the past decade engineering the setup and testing the atom’s properties.
How big is the improvement?
The sources differ on the margin. Live Science describes a 41% improvement over the previous record holder. Malay Mail says the clock is about four times as accurate as the earlier record holder, a calcium-ion clock from the Chinese Academy of Sciences in Wuhan. Malay Mail also says it surpasses an aluminium-ion clock that the US National Institute of Standards and Technology unveiled last year.
The gap may come from which accuracy measure or which earlier clock each outlet used. The articles do not explain it. Readers who want the exact comparison should check the Nature paper.
What it could change
Atomic clocks sit behind GPS, telecommunications and navigation systems. The SCMP notes that laboratories in the United States, China, Europe and Japan are competing to improve them.
There is a more formal goal too. Live Science reports that the international standards body BIPM is expected to redefine the second in 2030, using modern atomic clock technology. The second is currently defined by a microwave transition in caesium atoms. The Singapore team says its clock could become the new gold standard. Live Science says lutetium currently looks like the front-runner for accuracy.
That is not a decision. Accuracy is only one of several things standards bodies weigh, and other optical clocks are still improving. The team’s claim is that its design performs well and holds up in different environments.
The result also shows how a small group can lead in a field of large national labs. The SCMP framed the project as a decade-long effort by a small team that beat rivals in China and the US.
A clock this precise is not a consumer device. Its value lies in testing physics and setting the reference against which other clocks are measured. Better references make every downstream timing system easier to check.