a discovery awarded the 2022 Nobel Prize in Physics

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Advances in quantum physics alone challenge all of our beliefs about the world around us. This year, the Nobel Prize in Physics awards a trio of researchers who have reliably demonstrated, after 50 years of work, a more than controversial reality: the phenomenon of quantum entanglement – in which the quantum state of two particles is linked independently of the distance between them. to them. It is the basis for the development of current quantum computers and has made it possible to understand what Einstein called “terrifying action at a distance”.

Until the end of the 19th century, it was considered that reality was accessible to us and that scientists were external observers of phenomena that they could then describe objectively. Quantum physics, working within the infinitesimally small, sparks a lively debate about the relationship of science to reality.

In fact, we can objectively know the world around us by measuring it. But the act of measuring in the quantum world modifies and therefore disturbs the object studied. In fact, it is impossible to know its status before the measurement. Hence the question: are the particles “things” in themselves, can we attribute to them an autonomous physical reality outside of observation? Einstein amused himself by saying: Do you really think the moon isn’t there when you’re not looking at it? “. These are the bases of what is called quantum entanglement.

It should be known that quantum entanglement is the phenomenon in which two particles (or more) exist in the so-called entangled state, that is, despite the distance that separates them, they behave as a whole: a modification in one of them. them leads to a change in the other.

Working independently, each of the three researchers awarded the 2022 Nobel Prize in Physics has forged new experiments that demonstrate and study quantum entanglement. If an observer determines the state of such a particle, its entangled counterparts will instantly reflect that state, whether they are in the same room as the observer or in a galaxy on the other side of the universe! Their results established the violation of the so-called Bell inequalities and paved the way for new technologies based on quantum information, currently used to develop quantum computers, quantum cryptography, and the future quantum Internet.

Bell inequalities, a demonstration of quantum entanglement

First elucidated by Erwin Schrödinger in 1935, leading to his famous cat paradox, Albert Einstein dismissed entanglement as “terrifying action at a distance” and sparked a lengthy philosophical debate over the physical interpretation of quantum mechanics. Was it a complete theory or was it quantum entanglement due to “hidden variables” because its laws made no sense in the macroscopic world?

In 1964, CERN (European Organization for Nuclear Research) theorist John Bell proposed a theorem known as Bell’s inequalities, which put this question to the test. Specifically, he explains that in the case of hidden values, the correlation between the results of a large number of measurements will never exceed a certain value; on the contrary, if quantum mechanics is complete and therefore a valid theory, this value can be exceeded. Indeed, this is what is happening: all the experiments that have put these inequalities into practice, including those of the three Nobel laureates, show that they are violated and that quantum physics is indeed a complete theory.

Specifically, John Clauser (JF Clauser & Associates, USA) was the first to experimentally study Bell’s theorem, obtaining measurements that clearly violated a Bell inequality and thus supported quantum mechanics. Alain Aspect (University of Paris-Saclay and École Polytechnique, France) then put the results on firmer ground by figuring out ways to make measurements of entangled pairs of photons after they have left their source, thereby removing the effects of the environment on which they were issued. Eventually, using refined tools and a long series of experiments, Anton Zeilinger (University of Vienna, Austria) began using entangled quantum states to demonstrate, among other things, quantum teleportation, which allows a quantum state to be transferred from one particle to another.

As the CERN statement summarizes, these delicate and pioneering experiments not only confirmed quantum theory, but also laid the groundwork for a new field of science and technology, which has applications in computing, communication, sensing and simulation.

The Universe is not real locally, a basic tenet of quantum computing

Today, entanglement is accepted as one of the main features of quantum mechanics and is being implemented in cryptography, quantum computing, and a future “quantum internet” for more than a billion dollars a year. . One of his early successes in cryptography was sending messages using entangled pairs of photons, creating cryptographic keys securely: any eavesdropping will destroy the entanglement, alerting the recipient of the hack.

It would thus be a blatant illustration that the Universe is not locally real, as Nobel-winning scientists demonstrated this year. As explained in an article in american scientist, “real” means that objects have definite properties independent of observation: an apple can be red even when no one is looking at it, which is not the case in the quantum world. The properties of objects are interdependent on observation.

“Local” means that objects can only be influenced by their surroundings and any influence cannot travel faster than light. This is also not the case in quantum physics “because” of quantum entanglement. The trio of scientists have thus shown that objects are not only influenced by their environment, a modification in one particle will have repercussions on its entangled particle, several light years away, for example.

In 2017, Dr. Zeilinger used the technique via a Chinese satellite called Micius to have a 15-minute encrypted video call with Jian-Wei Pan of the Chinese Academy of Sciences, one of his former students. The satellite, built in part on the discoveries of John Clauser, uses various properties of quantum mechanics applied to photons, the elementary particles of light. The satellite is capable of manufacturing and emitting pairs of entangled photons, at two telescopes separated by 1,203 kilometers.

While acknowledging that the award honors future applications of his work, Dr. Zeilinger notes in an interview with New York Times : “ My advice would be: do what you find interesting and don’t worry too much about possible applications. For his part, Dr. Clauser says: I still confess today that I still don’t understand quantum mechanics, and I’m not even sure I know how to use it well. “.

However, in an article science newsNicolas Gisin, a physicist at the University of Geneva in Switzerland underlines: This award is well deserved, but it comes a bit late. Most of this work has been done in the [années 1970 et 1980]but the Nobel committee was very slow and is now rushing after the rise of quantum technologies “.

This boom is happening worldwide. Gisin concludes: In the United States, Europe and China, billions, literally billions of dollars are being invested in this area. So that completely changes. Instead of having a few pioneering people in the field, we now have a large number of physicists and engineers working together. “.

Although some of the quantum applications are in their infancy, the experiments of Clauser, Aspect, and Zeilinger introduce quantum mechanics and its implications into the macroscopic world. Their contributions validate some of the once-controversial key ideas of quantum mechanics and promise new applications that might one day find their way into everyday life.

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