The 2021 Nobel Prize in Physics has been awarded to three scientists whose work pioneered one of the most fascinating tests in the world of quantum mechanics, contradicting Einstein and discovering the strange phenomenon of quantum teleportation.
John F. Clauser, Alain Aspect, and Anton Zeilinger won the 10 million Swedish krona ($915,000) prize for “experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science,” the Royal Swedish Academy of Sciences, which is responsible for selecting the Nobel laureates in physics, announced Tuesday (Oct. 4).
The trio’s work focuses on quantum entanglement, a process in which two or more quantum particles are coupled so that any change in one particle will lead to a simultaneous change in the other, even if they are separated by vast, even infinite, distances. This effect gives quantum computers the ability to perform multiple calculations simultaneously, exponentially boosting their processing power over those of conventional devices.
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When the counterintuitive predictions proposed by quantum mechanics — of which quantum entanglement was one — were first discussed in 1935, not all physicists were comfortable with the implications. Albert Einstein dubbed the phenomenon “spooky action at a distance” and proposed that the effect actually came about because the particles contained hidden variables, or instructions, which had already predetermined their states. This would mean that there was no need for teleportation after all.
The three physicists who won today’s prize demonstrated that Einstein was wrong. Their practical experiments, built upon foundations first established in the 1960s by the theoretical physicist John Stewart Bell, showed that the physical world is best described not by the discrete billiard ball model of Newtonian physics, but rather by a model of wave-like particles that affect each other instantaneously across enormous distances.
“What today is considered logical, measurable and quantifiable was initially debated by Niels Bohr and Albert Einstein in philosophical terms. John Bell transformed the philosophical debate into science and provided testable predictions that launched experimental work,” Eva Olsson, a member of the Nobel committee for Physics, said during the committee’s announcement on Tuesday (Oct. 4). Olsson said that the three scientists who received this year’s prize “took up the challenges of Bell and tackled them in their laboratories.”
The work began in 1972, when John F. Clauser, an American physicist who is now the head of the J. F. Clauser and Associates research and consultancy firm, and his colleague Stuart Freedman devised the first test of Bell’s ideas by colliding calcium atoms to emit pairs of entangled photons (light particles) before passing them through filters to hit detectors. This experiment successfully showed that the state of one photon depended on how the other, on the opposite side of the experiment, was measured, and that the change occurred faster than light could travel. “Spooky action at a distance” — their results suggested — could, in fact, be real.
But some critics pointed to loopholes in the design of Clauser’s and Freedman’s experiment. One of the most important was that the measurement was pre-set, with the filters which caused the photons to pick their state being fixed before the light particles were sent flying. This meant that hidden information might still exist, with the observers selecting only photons whose states appeared closely bound, and ruling out others that might demonstrate a different result.
In 1980, Alain Aspect, a physicist at the Université Paris-Saclay, Paris, refined the experiment, making it more efficient and using a device to randomly switch the configuration of the filters so that the outcome of any measurement was no longer even remotely influenced by the experimenters. The results were the same as before. The evidence overwhelmingly pointed to quantum mechanics being instantaneous in its reach.
Then, in 1989, Austrian physicist Anton Zeilinger, of the University of Vienna, built upon these foundations, using a more sophisticated experimental design to entangle multiple photons and even demonstrating that it is possible to move all of the information about one particle to another. Zeilinger also showed that the effect still took place across enormous distances, with entangled particles 89 miles (143 kilometers) apart still behaving according to quantum predictions. This work enabled the creation of ever larger quantum networks, marking the beginnings of today’s fledgling quantum computers.
“Quantum information science is a vibrant and rapidly developing field. It has broad and potential implications in areas such as secure information transfer, quantum computing and sensing technology,” Olsson said. “Its predictions have opened doors to another world, and it has also shaken the very foundations of how we interpret measurements.”
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