by The 2022 Nobel Prize in Physics has been awarded to a trio of scientists for pioneering experiments in quantum mechanics, the theory that covers the microcosm of atoms and particles.
Alain Aspect from the Université Paris-Saclay in France, John Clauser from JF Clauser & Associates in the US and Anton Zeilinger from the University of Vienna in Austria will share the prize money of 10 million Swedish kronor (US$915,000 ) “for experiments involving photons, establishing the violation of Bell inequalities and pioneering the science of quantum information”.
The world of quantum mechanics seems very strange indeed. In school, we are taught 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 that. Rather than predicting individual results, it tells us the probability of finding subatomic particles in specific locations. A particle can actually be in many places at once, before we “pick” a position at random when we count it.
Even the great Albert Einstein himself was troubled by this – to the point where he was convinced it was wrong. Rather than the results being random, he reasoned that there must be some “hidden variables” – forces or laws that we cannot see – that predictably affect the results of our measurements.
Some physicists, however, embraced the implications of quantum mechanics. John Bell, a physicist from Northern Ireland, made a breakthrough in 1964, devising a theoretical test to show that the hidden variables Einstein had in mind do not exist.
According to quantum mechanics, particles can be “entangled”, so terrifyingly connected that if you manipulate one, you automatically and immediately manipulate the other.
If this eerie behavior—far apart particles mysteriously affect each other momentarily—were explained by particles communicating with each other via hidden variables, it would require faster-than-light communication between the two, which Einstein’s theories forbid.
Quantum entanglement is a challenging concept to understand, essentially linking the properties of particles no matter how far apart they are. Imagine a light bulb emitting two photons (particles of light) traveling in opposite directions away from it.
If these photons are entangled, then they can share a property, such as their polarization, regardless of their distance. Bell imagined doing experiments on these two photons separately and comparing their results to prove that they were entangled (actually and mysteriously connected).
Clauser put Bell’s theory into practice at a time when performing experiments on single photons was almost unthinkable. In 1972, just eight years after Bell’s famous thought experiment, Clauser showed that light could indeed become entangled.
While Clauser’s results were groundbreaking, there were some alternative, more exotic explanations for the results he obtained.
If light did not behave as physicists thought, perhaps its effects could be explained without involvement. These explanations are known as loopholes in Bell’s test, and Aspect was the first to question it.
Aspect did a clever experiment to eliminate one of the most important potential loopholes in Bell’s test. He showed that the entangled photons in the experiment do not actually communicate with each other via hidden variables to decide the outcome of Bell’s test.
This means that they are truly terrifyingly connected.
In science it is incredibly important to test concepts that we believe to be correct. And few have played a more important role in this than Aspect. Quantum mechanics has been tested time and time again over the past century and survived unscathed.
Quantum technology
At this point, you could be forgiven for wondering why it matters how the tiny world behaves, or that photons can get entangled. This is where Zeilinger’s vision really shines.
We once used our knowledge of classical mechanics to build machines, build factories, leading 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 that are capable of doing new things. Indeed, many believe it will lead the next revolution, that of quantum technology.
Quantum entanglement can be harnessed in computers to process information in ways not possible before. Detecting small changes in entanglement can allow sensors to detect things more precisely than ever before.
Communicating with entangled light can also guarantee security, as measurements of quantum systems can reveal the presence of the eavesdropper.
Zeilinger’s work paved the way for the quantum technological 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 submarine detection.
Ultimately, the 2022 Nobel panel recognized the importance of practical foundations that produce, operate and test quantum entanglement and the revolution it is helping to drive.
Glad to see this trio receiving the award. In 2002 I started a PhD at the University of Cambridge inspired by their work. The goal of my project was to make a simple semiconductor device to produce entangled light.
This was done to greatly simplify the equipment needed to do quantum experiments and allow the construction of practical devices for real-world applications. Our work was successful and it amazes and excites me to see the leaps and bounds that have been made in the field since then.
Robert Young, Professor of Physics and Director of the Lancaster Quantum Technology Centre, Lancaster University
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