Tiny quantum fluctuations observed moving 40-kg mirror

Physics is mostly divided into two areas – classical physics describes how large objects and systems work on a scale that we see every day, while quantum physics describes the “spooky” subatomic world. Now, scientists have observed a rare crossover, where a quantum fluctuation was able to affect a macroscale object.

To us living here in the world of classical physics, the realm of quantum physics sounds pretty counterintuitive. This is a world where particles can seemingly teleport through impenetrable barriers, communicate instantly over long distances, and exist in two states at once.

Most of the time, these quantum quirks are restricted to the microscopic world, where their effects are too tiny for us to notice. But now, physicists at MIT and LIGO have witnessed a quantum event affecting a macroscale object. It’s a bit like seeing a bad guy cop a kick from Ant-Man – things that small aren’t “supposed” to be able to affect us.

Quantum fluctuations are yet another phenomenon that sounds like science fiction to us. Basically, within seemingly empty space, particles constantly pop in and out of existence, creating a background of quantum noise.

And now, it turns out that this quantum noise is enough to move a macroscale object – at least, under very carefully controlled conditions. On a new study, researchers observed a quantum fluctuation giving a little kick to a 40-kg (88-lb) mirror at the LIGO laboratory. And we mean a little kick – the mirror was measured to have moved by about one sextillionth of a meter (10-20 m).

“A hydrogen atom is 10-10 meters, so this displacement of the mirrors is to a hydrogen atom what a hydrogen atom is to us – and we measured that,” says Lee McCuller, co-author of the study.

This kind of thing would be happening all around us, all the time, but usually there’s way too much interference to ever be able to observe it. To do so, the researchers turned to one of the “quietest” places on Earth – the LIGO facility.

LIGO is a huge laboratory set up to detect gravitational waves rolling in from deep space. These waves are ripples in the very fabric of spacetime, and by the time they wash over Earth, they’re distorting reality over a distance smaller than the width of a proton. To keep it sensitive enough to detect these events, the equipment is very well shielded from external noise.

That makes it uniquely qualified to potentially pick up macroscale movements from quantum fluctuations.

“What’s special about this experiment is we’ve seen quantum effects on something as large as a human,” says Nergis Mavalvala, co-author of the study. “We too, every nanosecond of our existence, are being kicked around, buffeted by these quantum fluctuations. It’s just that the jitter of our existence, our thermal energy, is too large for these quantum vacuum fluctuations to affect our motion measurably. With LIGO’s mirrors, we’ve done all this work to isolate them from thermally driven motion and other forces, so that they are now still enough to be kicked around by quantum fluctuations and this spooky popcorn of the universe.”

To maximize the quantum fluctuations, the researchers used an instrument called a quantum squeezer on LIGO’s laser. Quantum fluctuations emerge from the uncertainty principle – basically, the more precisely one property of a particle is measured, the less certain you can be sure of others. In this case, the two properties are phase and amplitude.

The quantum squeezer narrows down the uncertainty in phase, which increases the uncertainty in amplitude. The latter is the property most likely to impart a kick on the mirror, so essentially the team is boosting the chances that the mirror would move. And sure enough, it did.

“This quantum fluctuation in the laser light can cause a radiation pressure that can actually kick an object,” says McCuller. “The object in our case is a 40-kilogram mirror, which is a billion times heavier than the nanoscale objects that other groups have measured this quantum effect in.”

The study not only helps us understand the quirky quantum world better, but the team says that this quantum squeezer could eventually be used to help LIGO detect even fainter gravitational waves than it currently can.

The research was published in the journal Nature.

Source: MIT

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