Physicists at the National Institute of Standards and Technology (NIST) have built the most precise atomic clock in the world.
In a new study published in Physical Review Letters, the researchers say that their new clock’s uncertainty is 9.4x10-19. That incredibly small uncertainty means that it won’t gain or lose a second in 33 billion years, or two and a half times the estimated age of the universe. This makes it the most accurate atomic clock ever made.
So why does that matter? For most of us, we worry if our watches or phones are off by a few minutes, not a tiny fraction of a second. But a clock this precise can have implications way beyond punctuality.
Measuring time can be used to help infer position, making better clocks invaluable for things like GPS. In a world in which all clocks were perfectly calibrated and miniaturized, cars could send signals out and know where everything on the road was. As we veer towards self-driving cars, this technology could help us make major strides toward a world without crashes. The same tech could be put in boats or space shuttles.
Increasingly precise atomic clocks can also help redefine the second. This may not seem like a big deal, but could have ripple effects in everything from space travel to fundamental physics. The current definition of the second is based on the cesium ion, and the frequency of microwave beams needed to excite the electrons from one energy level to the next. That’s been the standard for decades, but researchers are optimistic that their method—which uses an aluminum ion and already outperforms the cesium standard by a factor of 100—could one day redefine the second.
With this kind of precision, researchers can start asking fundamental questions about physics. One area that scientists are excited to explore is Einstein’s theory of relativity.
“Take the case of special relativity. The idea is that a moving clock will run slower than a stationary clock,” lead author Samuel Brewer told Motherboard. “We’re not typically going fast enough to notice that this is happening, but with clocks this accurate we can measure it at a slow walking speed.”
Quantum clocks have also shown potential to change the way we think about the shape of our earth, conceptualizing it as a “geoid”—a hypothetical representation of Earth if the oceans were only influenced by the Earth’s rotation and gravity—in order to better understand these forces. Having a deep understanding of time can help scientists test some of our most fundamental theories, pointing toward new physics questions no one even knew to ask.
This new clock uses one single aluminum ion to measure time, making it a type of atomic clock called a quantum logic clock. The researchers trap the ion, isolating it from possible environmental disruptions, and hit it with a laser to cause its electrons to transition between orbits. These transitions make the “ticks” that measure time.
With this system, any movement of the ion can reduce the accuracy of the measurements, which make atomic clocks very difficult to build.
“You have a charged particle and it sits in a space where it gets pushed around by oscillating electric fields,” Brewer said. “Since it’s charged, it’ll move around with a field. We want that ion to sit still.”
To make that aluminum ion sit still, the researchers store it with a magnesium ion. They don’t want the aluminum ion to heat up, so they use lasers to cool that magnesium ion, indirectly sucking energy from the aluminum ion, too. This pulls aluminum back down to its motional ground state.
This clock is the leader in precision, but still lags behind other atomic clocks in stability. Brewer describes stability as how much “noise” is in the measurement, and is essentially how long a clock takes to measure the time. Another type of atomic clock—called the lattice clock—is more stable because it uses many atoms instead of just one.
Using a lot of atoms helps reduce the “noise,” but makes the clock much more susceptible to the kind of environmental disruptions that the single-ion clock avoids. Researchers are working to reduce this trade off, testing the clocks against each other to try to improve both.
“These are very powerful tools that essentially fit on a tabletop,” Brewer said. “They may point towards new physics we don’t understand.”