A group of Dutch physicists have shown that one of the weirdest, most puzzling ideas in the universe is real.
The idea is part of quantum mechanics, a theory of physics that describes how the cosmos works on the tiniest of scales. Specifically, scientists are squirming over a bizarre phenomenon of quantum mechanics called “entanglement,” where one particle can instantly influence another — even from opposite sides of the universe.
If this Dutch experiment holds up and the idea of entanglement is real, it might lead to the development of unbreakable codes, the most precise clocks ever made, and superfast computers, to name a few applications.
The study was published this month in the journal Nature.
What is ‘entanglement?’
According to physics theories pioneered by Albert Einstein, nothing can travel faster than the speed of light, so it should be impossible for information from one particle to travel instantaneously to another.
That’s why Einstein famously rejected quantum mechanics and called entanglement “spooky action at a distance.” He refused to accept that the universe operated in such a strange, seemingly inexplicable way.
Physicists are still arguing over whether this “spooky action” exists or not.
It sounds like magic, but in quantum mechanics, particles can also exist in multiple states at the same time. This is called superposition. But as soon as you try to measure them and see what state they’re in, their strange quantum state collapses and you’re left with two regular particles.
It’s sort of like the fairy tale idea that toys (or the weeping angels in Doctor Who) come to life when we have our backs turned to them, but as soon as we turn around, they return to their original position as quick as lightning. Or Schrödinger’s famous thought experiment, where a cat in a box can either be alive or dead until you open it up and check.
Putting it to the test
So how do we figure out if quantum entanglement is real?
Scientist John Bell designed an experiment to prove quantum entanglement. It involves entangling particles, separating them, moving them off in different directions, and then measuring to see if they maintain that “spooky” connection even while physically separated.
You can watch a detailed explanation of a Bell test in the video below:
Many physicists have performed versions of the Bell test, and most of the results suggest quantum entanglement is real. But critics say all the experiments — so far — left too much room for loopholes and other possible explanations for the strange phenomenon.
The researchers behind the latest attempt describe their experiment as a “loophole-free Bell test,” but other physicists disagree.
“The experiment has closed two of the three major loopholes beautifully, but two out of three isn’t three,” Dr. Kaiser told The New York Times. “I believe in my bones that quantum mechanics is the correct description of nature. But to make the strongest statement, frankly we’re not there.”
The new experiment
That said, this particular experiment came closer than many others to being truly loophole-free.
According to the research paper, the physicists made two diamond traps to capture a single electron — one per diamond — and used superfast laser pulses to “entangle” the electrons at a close distance. Next, they separated the diamonds almost a mile apart on Delft University’s campus in The Netherlands:
Remember superposition, where a particle can exist in multiple states at once? Electrons only have two possible states: They have a magnetic property called “spin” where they can point either up or down. When we’re not looking at them, they can point both up and down at the same time. As soon as we look, though, their spin changes to either up or down.
The weird entangled link between the electrons means that the measurement of one particle’s spin instantly defines the other particle’s spin. So if one electron is measured as “up,” quantum mechanics says its partner must be “down” if the two were truly entangled.
For their experiment, the physicists painstakingly set up the diamonds and lasers in a way that made it possible to measure one pair of electrons at a time — getting rid of one loophole. Closing a second loophole, they set up the diamonds far enough apart that there was no way the electrons inside could interact other than by entanglement.
Based on the measurements of 245 pairs of entangled electrons, the team confirmed that each electron really was exerting “spooky action” on its entangled partner; whenever they measured one electron, the other electron across campus instantly flipped.
The one loophole remaining that might explain the weird behaviour is the influence of nearby, unentangled electrons. Accounting for this may involve measuring all the electrons at the same location as the entangled electron, which might be impossible (electrons are everywhere).
Despite its flaw, the new experiment could be a big step forward in determining if all the strange rules of quantum mechanics are real.
And if we can learn to harness quantum entanglement, experts think it help us send perfectly encrypted messages around the world, create the most precise atomic clocks ever built, and provide computer engineers with insight to build the first working, practical quantum computers.
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