Nobel prize: physicists share prize for insights into the spooky world of quantum mechanics

The 2022 Nobel Prize in Physics has been awarded to three scientists for groundbreaking experiments in quantum mechanics, the theory about the microworld of atoms and particles.

Alain Aspect of the Université Paris-Saclay in France, John Clauser of JF Clauser & Associates in the US, and Anton Zeilinger of the University of Vienna in Austria, will share the prize money of 10 million Swedish kronor (US$915,000) “for experiments with entangled photons, establishing the violation of Bell inequality, and pioneering quantum information science.”

The world of quantum mechanics seems very strange indeed. We are taught in school that we can use equations in physics to predict exactly how things will behave in the future — where a ball will go if we roll it down a hill, for example.

Quantum mechanics is different from this. Instead of predicting individual outcomes, it tells us the probability of finding subatomic particles in certain places. A particle can actually be in several places at once, before we randomly “choose” one location when we measure it.

Even the great Albert Einstein himself was confused by this – to the point where he was convinced it was wrong. Rather than the outcomes being random, he thought there must be some “hidden variables” — forces or laws we can’t see — that predictably influence the results of our measurements.

However, some physicists embraced the implications of quantum mechanics. John Bell, a physicist from Northern Ireland, made a major breakthrough in 1964 and devised a theoretical test to show that the hidden variables Einstein had in mind do not exist.

According to quantum mechanics, particles can be “entangled”, ghostly connected, so that if you manipulate one, you automatically and immediately manipulate the other. If this ghostlyness – particles that are far apart and mysteriously affect each other immediately – were explained by the particles communicating with each other through hidden variables, then communication between the two would be necessary faster than light, which Einstein’s theories suggest. forbid.

Quantum entanglement is a challenging concept to understand, essentially connecting the properties of particles, regardless of how far apart they are. Imagine a light bulb emitting two photons (particles of light) moving away from the bulb in opposite directions.

If these photons are entangled, they can share a property, such as their polarization, regardless of their distance. Bell envisioned conducting experiments on these two photons separately and comparing their results to prove that they were entangled (real and mysteriously connected).

Clauser put Bell’s theory into practice at a time when single photon experiments were almost unthinkable. In 1972, just eight years after Bell’s famous thought experiment, Clauser showed that light can indeed be entangled.

While Clauser’s results were groundbreaking, there were a few alternative, more exotic explanations for the results he obtained.

If light did not behave quite as the physicists thought, perhaps its results could be explained without entanglement. These statements are known as loopholes in Bell’s test, and Aspect was the first to challenge them.

Aspect devised an ingenious experiment to rule out one of the main potential loopholes in Bell’s test. He showed that the entangled photons in the experiment don’t actually communicate with each other through hidden variables to determine the outcome of Bell’s test. This means they are really spooky connected.

In science, it’s incredibly important to test the concepts we think are correct. And few have played a more important role in this than Aspect. Quantum mechanics has been tested over and over over the past century and has survived unscathed.

Quantum technology

At this point, you may be forgiven for wondering why it matters how the microscopic world behaves, or whether photons can get entangled. This is where Zeilinger’s vision really shines.

We once used our knowledge of classical mechanics to build machines, to make factories, which led to the industrial revolution. Knowledge of the behavior of electronics and semiconductors has driven the digital revolution.

But understanding quantum mechanics allows us to exploit it, to build devices capable of doing new things. Indeed, many believe it will drive the next revolution of quantum technology.

Quantum entanglement can be used in computers to process information in ways that were not possible before. By detecting small changes in entanglement, sensors can detect things with greater precision than ever before. Communicating with entangled light can also guarantee security, as measurements from quantum systems can reveal the presence of the eavesdropper.

Zeilinger’s work paved the way for the quantum technology revolution by showing how it is possible to link a series of entangled systems together to build the quantum equivalent of a network.

In 2022, these applications of quantum mechanics are not science fiction. We have the first quantum computers. The Micius satellite uses entanglement to enable secure communications around the world. And quantum sensors are used in applications from medical imaging to detecting submarines.

Ultimately, the 2022 Nobel Panel recognized the importance of the practical basis for producing, manipulating, and testing quantum entanglement and the revolution it helps spark.

I am happy that this trio can receive the prize. In 2002 I started a Ph.D. at the University of Cambridge who was inspired by their work. The goal of my project was to create a simple semiconductor device to generate entangled light.

This was intended to greatly simplify the equipment needed to conduct quantum experiments and to build practical devices for real-world applications. U.S work was successful and it amazes and excites me to see the leaps and bounds that have been made in the field since then.

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