The 2022 Nobel Prize in Physics was awarded for their work on “quantum entanglement”: a phenomenon so strange and impossible that even Albert Einstein didn’t believe it. And he described it as “terrifying.”
Even today, many physics graduates still don’t understand the phenomenon of entanglement, also known as “entanglement,” says physicist Chris Phillips of Imperial College London.
He takes the example of a photon, a particle of light. By passing it through a special crystal, two photons come out. “They are not the same color as the original, but because they come from the same photon, they are entangled,” he explains to AFP.
The measurement of properties which we undertake in one, by examining it, immediately affects the other, whatever the distance separating them. Two entangled particles behave in the same way as if they were connected by an invisible thread.
Chris Phillips saw this “very strange thing” in his lab, consisting of two entangled photon beams. “I can put my hand on this 2nd beam,” he says, “and something immediately happens on the second beam on the other side of the room, which is proven by an instrument.”
It was this idea of immediacy that bothered Einstein, because matter or information cannot travel faster than the speed of light.
In 1935, the founder of relativity questioned a key component of quantum entanglement, non-locality, which he described as the “spooky effect at a distance”. Because it violates the principle of locality according to him, which means that an object can only affect its immediate environment.
To explain the effect of the problem, he postulates the existence of “hidden variables”, i.e. forces at work, but not yet known.
In 1964, Northern Irish physicist John Stewart Bell found a way to verify this with an inequality theorem that bears his name. But it still needs to be put to the test of scientific experimentation.
French physicist Alain Aspect achieved this in his laboratory two decades later. This demonstrates that two entangled particles of light are entangled in such a way that a measurement of the properties of one immediately affects the properties of the other.
By testing its limits, he and his team have demonstrated that “quantum mechanics is resistant to all possible attacks,” Alain Aspect said in an interview published by the Nobel Foundation on Tuesday after being awarded his prize.
This reward certainly proves Einstein wrong, but the French physicist is very grateful to him.
“I would like to say that Einstein gets a great deal of credit for raising the question of non-locality, which is one of the foundations of the problem, which underlies the Alain aspect.
He himself admits the difficulty of accepting the concept of non-locality as “a mental image, absolutely insane”.
His co-winners of the Nobel Prize in Physics, the Austrian Anton Zeilinger and the American John Glaser, have also tested Bell’s theorem and ruled out any other non-local explanation. Their work paved the way for the so-called “second quantum revolution”.
Known as the “famous man of quantum”, Zeilinger’s discoveries showed potential applications of entanglement in encrypted communications, quantum teleportation, and more.
High-tech companies are investing huge funds in the development of quantum computers that promise unparalleled computing capabilities.
Chris Phillips, for his part, has developed an instrument the size of a high-fidelity stereo that uses quantum entanglement to detect breast cancer.
But the biggest mystery of quantum entanglement remains unsolved a century after it fascinated Albert Einstein: How does it happen?
“We need to be humble about physics,” says Chris Phillips. “It simply is”.