Time: It bends and curves, or appears to speed up or slow down, depending on your position or perception. So precisely measuring its passage is one of the most fundamental tasks in physics—and could help us land on Mars or even observe dark matter.
Now, physicists from 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 “web” of light to capture and excite a diffuse cloud of cold strontium atoms.
“This clock is so precise that it can detect tiny effects predicted by theories like general relativity, even on microscopic scales,” said Jun Ye, a physicist at NIST’s Joint Institute for Laboratory Astrophysics (JILA) lab at the University of Colorado. “It pushes the boundaries of what’s possible with timekeeping.”
With a total systematic accuracy of 8.1 x 10-19The strontium clock is twice as accurate and more precise than the previous record holder.
NIST is a place where researchers experiment with technologies to improve the accuracy of globally standard measurements, such as the international unit of time (the second).
While a solid block of material can be used to represent a unit of mass, time lacks an enduring physical property that we can return to for consistent measurement. Instead, we rely on patterns that repeat reliably, such as the rotation of the Earth, the swing of a pendulum, or the hum of an electrified piece of quartz.
Predictable as they all are, even the rotation of the Earth slows down and speeds up in increments. Finding patterns in nature that can be measured in ways that vary by the tiniest of degrees would lead to ever more precise measurements of timekeeping.
One such pattern is the jitter of excited electrons surrounding an atom. For example, the standard second is defined by the “jump” of specific electrons orbiting a cesium atom. Excited by microwaves of a certain frequency, they launch into higher energy states and back again 9,192,631,770 times per second.
Today’s best cesium atomic clocks, first developed in 1955 and improved since then, keep time to within three hundred millionths of a second per year. For comparison, your quartz wristwatch is about 180 seconds (or 3 minutes) per year off or on.
However, geometers are considering redefining the second in the coming decade as atomic clock technology advances rapidly.
In the past two decades, atomic clocks have emerged that excite atoms or ions with light of shorter wavelengths than microwaves, breaking records for stability and accuracy.
This new atomic clock, developed by JILA physicist Alexander Aeppli and colleagues, is atomically speaking significantly better than the previous best optical lattice clock, which Ye and other JILA colleagues helped develop in 2019.
“It is the precision benchmark of all optical clocks reported to date,” Aeppli, Ye and colleagues write in their preprint describing the new clock.
In its one-dimensional ‘web’ of laser light, the clock captures tens of thousands of strontium atoms, providing a higher level of precision. The shallow web of light, which operates in an ultra-high vacuum on a thin layer of supercold strontium atoms, also minimizes errors by reducing the destabilizing effects of the lasers and atoms colliding with each other.
With this precision as the basis for accuracy, the clock is expected to lose time by only one second every 30 billion years – which could help space travelers keep track of time over vast distances.
“If we want to land a spacecraft on Mars with extreme accuracy, we need clocks that are much more accurate than what we have now in GPS,” Ye said. “This new clock is a big step toward making that possible.”
Increasingly precise clocks can also detect tiny deviations in the vibrations of the atoms, which could indicate a weak interaction with dark matter or the relativistic pull of gravity.
“Every gain in stability and accuracy opens up new areas of research, such as establishing limits on dark matter [or] “Exploring general relativity,” the researchers write.
But there may be other ways to reach these new frontiers, beyond 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 make more stable timekeeping devices.
The research was published on the arXiv preprint server, prior to its publication in Physical assessment lettersa peer-reviewed journal.