What is Quantum Entanglement?

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What is Quantum Entanglement?

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The 2022 Nobel Prize in Physics has honored three scientists for their breakthrough contributions to our understanding of one of the most mysterious of all natural phenomena: quantum entanglement.

Simply put, quantum entanglement is the dependence of the sides of one particle in an entangled pair on the sides of the other particle, no matter how far apart they are or what lies between them. These particles could be electrons or photons, for example, and one aspect could be their state, such as whether it is “rotating” in either direction.

The peculiarity of quantum entanglement is that when he in an entangled pair measures something about one particle, he immediately knows about the other, even millions of light-years away. This strange connection between two particles is fleeting and seems to break the fundamental laws of the universe. Albert Einstein called the phenomenon “a distant and spooky action.”


After spending the better part of 20 years experimenting with roots in quantum mechanics, I’ve learned to come to terms with its weirdness. Thanks to increasingly accurate and reliable instruments and the work of this year’s Nobel laureates Alan Aspect, John Krauser and Anton Seilinger, physicists are now very certain that quantum phenomena are the world’s Integrated with knowledge.

However, until the 1970s, researchers were divided on whether quantum entanglement was a real phenomenon. And for good reason – who would oppose the great Einstein who dared to doubt it? It took the development of new experimental techniques and courageous researchers to finally unravel this mystery. exist in multiple states at once

To truly understand the eerie nature of quantum entanglement, it is important to first understand quantum superposition. Quantum superposition is the idea that particles exist in more than one state at the same time. It is as if the particle chooses one of the states of the superposition when the measurement is made. For example, many particles have an attribute called spin, which is measured as ‘up’ or ‘down’ relative to a particular direction of the analyzer. However, until we measure the spin of a particle, it exists simultaneously in a superposition of spin-up and spin-down. Each state is associated with a probability, allowing us to predict the average outcome from many measurements. The probability that a single measurement will rise or fall depends on these probabilities, but is itself unpredictable.

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Although very strange, mathematics and numerous experiments have shown that quantum mechanics correctly describes physical reality. two intertwined particles

The eerie nature of quantum entanglement stems from the reality of quantum superposition and was evident to the founder of quantum mechanics as he developed the theory in the 1920s and his 1930s.

To create entangled particles, we basically decompose the system into two parts. The sum of these parts is known. For example, a particle with zero spin can be split into two particles with necessarily opposite spins so that their sum equals zero.

In 1935, Albert He Einstein, Boris Podolsky, Nathan He Rosen published a paper describing a thought experiment aimed at explaining the apparent absurdity of quantum entanglement, which challenges the fundamental laws of the universe.

A simplified version of this thought experiment is due to David Bohm and considers the decay of particles called pions. When this particle decays, it produces electrons and positrons with opposite spins that move away from each other. Therefore, if the electron spin is measured up, the measured positron spin may be down, and vice versa. This is true even if the particles are billions of kilometers apart.

If the measured electron spin is always on top and the positron’s measured spin is always on the bottom, that’s fine. However, due to quantum mechanics, each particle’s spin will be both partially up and partially down until it is measured. Only when the measurement is made does the quantum state of the spin “collapse” up or down, and the other particle immediately collapses to the opposite spin. This seems to indicate that the particles communicate with each other via means that travel faster than the speed of light. But according to the laws of physics, nothing can travel faster than the speed of light. Couldn’t the measured state of one particle instantly determine the state of another particle on the other side of the universe?

Physicists, including Einstein, proposed many alternative interpretations of quantum entanglement in the 1930s. They theorized that there are unknown properties, called hidden variables, that determine the state of the particles before they are measured. However, physicists at the time had neither a clear measurement technique nor a definition that could be used to test whether quantum theory needed to be modified to include hidden variables.

Disproving The Theory

There was no evidence of an answer until the 1960s. John Bell, a brilliant Irish physicist who didn’t live to see the Nobel Prize, devised a plan to test whether the concept of hidden variables made sense.

Bell established the equation now known as Bell’s inequality. This is always and only true for hidden variable theory, and not always true for quantum mechanics. Therefore, if Bell’s equation is found not to hold in actual experiments, local hidden variable theory can be ruled out as an explanation for quantum entanglement.

The experiments of the 2022 Nobel Prize winners, especially Alan Aspect, were the first tests of Bell’s inequality. The experiment used entangled photons rather than electron-positron pairs as in many thought experiments. The results conclusively ruled out the presence of hidden variables, mysterious attributes that predict the state of entangled particles. Collectively, these and many subsequent experiments confirmed quantum mechanics. Objects can be related over long distances in ways that pre-quantum mechanical physics cannot explain. The important thing is that it does not contradict special relativity, which prohibits faster-than-light communication. The fact that measurements over long distances are correlated does not imply that information is transferred between particles. His two distant parties making measurements of entangled particles cannot use this phenomenon to pass information faster than the speed of light.

Today, physicists continue to study quantum entanglement and explore its potential applications. Quantum mechanics can predict the probability of a measurement with incredible accuracy, but many researchers are skeptical that it provides a complete explanation of reality. One thing is certain, though. Much remains to be said about the mysterious world of quantum mechanics.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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