Think back to our video call gone wrong from earlier. You need to be able to hear what your colleagues are saying, so you make a choice to decrease audio uncertainty and increase video uncertainty by lowering the video quality. The faces of the other participants on the call may become too pixelated and distorted to see, but you can hear them clearly now. Conversely, if someone on the call is trying to show you a visual detail, you may want to decrease audio quality in favor of increasing the video’s clarity.

Scientists do something like this when employing quantum squeezing. If a researcher needs to know a quantum signal’s amplitude, they can use devices called ​“squeezers” to squeeze a quantum system — such as a beam of light — and decrease amplitude uncertainty at the cost of increased phase uncertainty. Much like your video call, it’s about deciding where measurement precision can be sacrificed.

Quantum squeezing has enormous potential for future technologies, providing a method to improve the measurement sensitivity of properties at nature’s tiniest scales.

Practical Applications

While our video call analogy here is meant to help you understand quantum squeezing using something that exists at the human scale, true quantum squeezing happens at a minuscule scale that is hard for humans to imagine.

High-precision timekeeping is a good example of quantum squeezing’s value. The watch on your wrist is accurate enough for many activities, but it’s too imprecise to measure ultrashort time lapses. For instance, clocks in space run a tiny bit faster than clocks based on Earth, thanks to variations in gravity. This gravitational time dilation is a part of Einstein’s theory of general relativity, where time is experienced slower the closer one is to a massive object like the Earth.

A simple wristwatch can’t detect these minuscule alterations of time. But an atomic clock can. The most accurate of these are so precise that if they’d been running since the Big Bang, they wouldn’t be off by more than a single second today. This level of precision is why GPS satellites rely on atomic clocks to stay in contact with Earth-bound devices. For instance, a clock on a passenger plane will tick slightly faster in the air than it will on the ground, and an atomic clock on a satellite can help correct these tiny variations.

These useful gadgets work by taking atoms — cesium atoms are common ­— and counting their electrons’ oscillations under specific conditions. Every cesium atom in the entire universe will oscillate at the exact same rate, which means a cesium atomic clock on Earth will keep the same time as a cesium atom that we’ve shot out into space.

Within this system, noise can interfere with accurate readings of the clock. Scientists use quantum squeezing to lower that noise. The oscillations of the electron can be seen as similar to the swinging pendulum of a grandfather clock. In this analogy, the phase of the electron refers to the starting point of each swing of the pendulum. By squeezing the phase at the expense of an uncertain amplitude, the scientists are able to ensure that each swing of the pendulum — each oscillation of the electron — is predictably measurable.

The applications for quantum squeezing also reach for the stars. Kasevich describes how the Laser Interferometer Gravitational-wave Observatory (LIGO) squeezes light from distant celestial objects. The technology allowed the LIGO team to be the first in history to physically sense the gravitational waves created by two colliding black holes about 1.3 billion light-years away.

“The LIGO gravitational wave detectors are using squeezing on their beams of light to improve the precision of the interferometers, which measure the phase differences between two beams of light,” Kasevich said. ​“This has fantastic science consequences because you get more precision. The better the precision, the greater the volume of the universe where we can actually detect a gravitational wave source. By just getting a factor of two more precision, when they use squeezing, they improve their ability to make a discovery by nearly a factor of 10.”

And that’s the beauty of quantum squeezing — we simply don’t know what observations we’re missing right now. The most beautiful song in the world means nothing if the lawnmower next door is drowning it out. Similarly, we can’t know what gravitational waves we’re missing in the quantum realm until we reduce uncertainties.