Time: Bends and warps, or appears to speed up or slow down, depending on your position or perception. Accurately measuring its passage is therefore one of the most fundamental tasks in physics – one that 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 to date, using a “web” of light to trap and excite a diffuse cloud of cold strontium atoms.
“These clocks are so precise that they can detect tiny effects predicted by theories like general relativity, even on a microscopic scale,” says Jun Ye, a physicist at NIST’s Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. . “It pushes the boundaries of what’s possible with timing.”
With an overall systematic precision of 8.1 x 10-19the strontium clock is twice as accurate and precise as the previous record holder.
NIST is where researchers pursue technologies to increase the accuracy of global standard 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 permanent physical property that we can fall back on for consistent measurement. Instead, we rely on patterns that repeat themselves in reliable ways, like the rotation of the Earth, the swing of a pendulum, or the hum of an electrified piece of quartz.
Predictably, even the Earth’s rotation gradually slows and speeds up. Finding patterns in nature that can be measured in ways that differ by the smallest degrees would lead to ever more accurate measurements of time.
One such pattern is the jitter of excited electrons surrounding an atom. For example, a standard second is defined by the “hopping” of specific electrons orbiting a cesium atom. Energized by microwaves of a certain frequency, they launch into higher energy states, and 9,192,631,770 times per second they reverse again.
First developed in 1955 and continuously improved since then, today’s best cesium atomic clocks keep time to within one three hundred millionth of a second per year. In comparison, your quartz wristwatch loses or gains about 180 seconds (or 3 minutes) each year.
However, measurement scientists are considering redefining the latter in the next decade as atomic clock technologies advance rapidly.
In the last two decades, atomic clocks, which excite atoms or ions with shorter wavelengths 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 benchmark for the accuracy 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, offering a higher level of precision. The shallow web of light that acts in an ultra-high vacuum on a thin layer of supercold strontium atoms also minimizes errors by reducing the destabilizing effects of lasers and colliding atoms.
With this precision underlying its accuracy, the clock is expected to lose only one second every 30 billion years – which could help space travelers keep time over vast distances.
“If we want to land a spacecraft on Mars with absolute precision, we’re going to need clocks that are orders of magnitude more accurate than what we have in GPS today,” Ye says. “These new hours are a significant step towards making that possible.”
Increasingly accurate clocks can also detect small variations in the oscillations of atoms that may signal a weak interaction with dark matter or the relativistic pull of gravity.
“Each gain in stability and precision opens up new areas of investigation, such as determining the limits of dark matter [or] investigation of general relativity,” the researchers write.
But there may be other ways to reach these new frontiers besides optical atomic clocks. Researchers have also experimented with using quantum entanglement to keep time and exciting atomic nuclei, rather than whole atoms, with lasers, which could be used to create more stable time-keeping devices.
The research was published on arXiv preprint server, before its publication in Physical Review Letterspeer reviewed journal.