Physicists at the University of Toronto have developed the first of a new generation of optical atomic clocks with the potential to be a hundred times more accurate than those currently in use.
The new technology would help advance the replacement of legacy cesium clocks that have been in use for decades to define the length of the second and ensure precise timekeeping.
“Accurate measurements of time and frequency underlie our entire system of physical units,” says Associate Professor Amar Vutha. “Therefore, improving the accuracy of timekeeping devices leads to stronger foundations for every physical measurement.”
Vutha is an experimental physicist in the Faculty of Arts & Science’s Department of Physics; Takahiro Tow is a PhD student in the department. Building on the contributions of previous team members, they have developed the world's first cryogenic single-ion trap for regulating the accuracy of an atomic clock.
All timekeeping devices rely on a mechanism that generates a consistently repeating interval or “ticking” — whether it’s a swinging pendulum or a vibrating quartz crystal in a wristwatch.
“In every good clock, the periodic event must be stable,” explains Vutha. “It wouldn't do for it to run faster occasionally and then slower.
“In an atomic clock, the ticking is the oscillations of electromagnetic fields in a laser. And the stable periodicity of the laser is ensured by an atom; the quantum vibrations of the atom work like a tuning fork to keep the laser ‘in tune.’”
The first generation of optical atomic clocks used microwaves, regulated by cesium atoms. The next generation used visible light lasers. Because the frequency of the visible light of optical lasers is some 100,000 times higher than that of masers, this second generation of optical atomic clocks is magnitudes more precise, with an accuracy measured to 18 decimal places — or the equivalent of measuring the distance from the Earth to the moon to one millionth of a millimetre.
Vutha and Tow’s third-generation atomic clock also uses optical light. Using electromagnetic fields, they trap a single strontium atom which, when synchronized with the laser, ensures stability and accuracy.
But says Vutha, “The regulating atoms in current optical atomic clocks are still perturbed by infrared light — heat — emitted by nearby objects, including the metal vacuum container around it. This limits their accuracy because, if the tuning fork itself goes out of tune, then you no longer have a stable clock.”
Vutha and Tow's breakthrough is to cool the strontium atom to less than five degrees Kelvin; i.e. five degrees above absolute zero. Operating the device at close to absolute zero eliminates the thermal radiation that currently limits the accuracy of other single-ion clocks.
Perhaps not surprisingly, a function as universally fundamental as timekeeping has important applications and deep ramifications.
For example, the definition of the standard of current — the ampere — requires measuring the number of electrons that flow through a device within an accurately calibrated time interval. Similarly, one volt is defined fundamentally in terms of the frequency of oscillations produced in a certain device when a voltage difference is applied across it.
“What’s more,” says Vutha, “I would say that the most successful application of the new generation of optical clocks has been to test whether the fundamental constants of nature — the speed of light, Planck's constant, etc. — are themselves constant. Even though we call them constant, we aren’t quite sure.
“So, atomic clocks can be used to check whether these fundamental constants are actually constant. And while that may not be immediately applicable science, it is very fundamental. And there’s just no other way of doing these kinds of experiments than with atomic clocks.”
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Nov. 25, 2025 | Toronto Star