Time: Bends and warps, or seems to speed up or slow down, depending on your position or perception. So accurately measuring its passage is one of the most fundamental tasks in physics – which could help us land on Mars or even observe dark matter.
Now, physicists at the US National Institute of Standards and Technology (NIST) and the University of Delaware have developed the most accurate and precise atomic clock yet, using a ‘net’ of light to capture and excite a diffuse cloud of atoms cold strontium.
“This clock is so precise that it can detect tiny effects predicted by theories such as general relativity, even at the microscopic scale,” says Jun Ye, a physicist at NIST’s Joint Institute for Laboratory Astrophysics laboratory ( JILA) at the University of Colorado. . “It’s pushing the boundaries of what’s possible with timing.”
With a total systematic precision of 8.1 x 10-19the strontium clock is twice as accurate and precise as the previous record holder.
NIST is a place where researchers tinker with technologies to increase the accuracy of standard global measurements, such as the international unit of time; second.
Where a solid block of material can be used to represent a unit of mass, time lacks a stable physical property that we can fall back on for a consistent measurement. Instead, we rely on patterns that repeat themselves in reliable ways, such as the rotation of the Earth, the swing of a pendulum, or the hum of an electrified piece of quartz.
As predictable as each is, even the Earth’s rotation slows and speeds up in increments. Finding patterns in nature that can be measured in ways that differ from smaller scales would lead to increasingly accurate timekeeping measures.
One such pattern is the vibration of excited electrons surrounding an atom. The standard second, for example, is determined by the ‘hopping’ of specific electrons orbiting a cesium atom. Energized by microwaves of a certain frequency, they are released into higher energy states and bounce back 9,192,631,770 times per second.
First developed in 1955 and improved since then, today’s best cesium atomic clocks keep time to within three hundred millionths of a second per year. Your quartz wristwatch, by comparison, loses or gains about 180 seconds (or 3 minutes) each year.
However, measurement scientists are considering redefining the second in the next decade because atomic clock technologies are advancing rapidly.
In the last two decades, atomic clocks that excite atoms or ions with wavelengths shorter than microwaves have come to the fore, setting records for stability and accuracy.
This new atomic clock, developed by JILA physicist Alexander Aeppli and colleagues, is atomic leaps ahead of the previous best optical lattice clock, which Ye and other JILA colleagues helped develop in 2019.
“It sets the standard for the precision of all optical clocks reported to date,” Aeppli, Ye and colleagues write in their preprint, describing the new clock.
In its one-dimensional ‘grid’ of laser light, the watch captures tens of thousands of strontium atoms, offering a higher level of precision. The shallow light grating, operating in an ultra-high vacuum on a thin layer of super-cold strontium atoms, also minimizes errors by reducing the destabilizing effects of lasers and colliding atoms.
With this accuracy underpinning its accuracy, the clock is expected to lose just one second every 30 billion years – which could help space travelers keep time over great distances.
“If we want to land a spacecraft on Mars with pinpoint accuracy, we’re going to need clocks that are orders of magnitude more accurate than what we have today in GPS,” Ye says. “This new watch is a big step towards making that happen.”
The increasingly precise clocks can also register small deviations in the oscillations of atoms, which could signal a weak interaction with dark matter or the relativistic pull of gravity.
“Each gain in stability and precision opens up new areas of exploration, such as setting limits on dark matter [or] investigating general relativity,” the researchers write.
But there may be other ways to reach those new limits besides optical atomic clocks. Researchers have also experimented with using quantum entanglement to keep time, and exciting atomic nuclei, not whole atoms, with lasers, which could be used to create more stable time-keeping devices.
Research is posted on arXiv preprint server, before its publication on Physical review papersa peer-reviewed journal.