**Alain Aspect, John F. Clauser, and Anton Zeilinger** are awarded the **Nobel Prize 2022 in Physics** for their work with entangled photons, which proved the violation of Bell inequalities and laid the groundwork for quantum information science.

Matter and its interactions with energy at the atomic and subatomic scales are the focus of quantum mechanics. Under very specific circumstances, quantum entanglement can emerge through interactions between two or more of these particles. In other words, the quantum state of each interacting particle, irrespective of its proximity to other particles, can no longer be explained independently of other shared particles. As one of several quantum theories that distinguish quantum mechanics from classical mechanics, this one has been the subject of considerable discussion ever since it was first proposed. These entangled quantum states have been investigated by this year’s laureates, and their experiments formed the basis for the present quantum technology revolution.

Researchers from all over the world have been puzzling over the nature of entangled states and the effects they have on the quantum states and properties of the particles involved for a long time. The three Nobel laureates set out on a quest to explore these mysteries by doing ground-breaking experiments using entangled particles. Despite the fact that the term “entanglement” was coined by Erwin Schrödinger, the concept of entanglement was first formulated by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935, when they proposed a thought experiment, dubbed the EPR paradox. The experiment used two particles in an entangled state, and the physicists noted that the properties of the other particle may be predicted if the properties of one of the particles are observed, which goes against the established characteristics of quantum mechanics. Therefore, they concluded that the current understanding of quantum mechanics is insufficient to characterize these entangled states.

After a long debate on the existence of hidden variables to explain this phenomenon, John Bell formulated Bell’s inequality in 1964, analytically demonstrating that no hidden variable theory would be able to duplicate all the results of quantum physics. The result will satisfy the inequality if and only if the statistical correlation between the entangled particles can be explained by local hidden variables. In other words, if there are hidden variables, the correlation between the results of several measurements will always be below some threshold. If an experiment is designed in a certain way, however, quantum mechanics predicts that Bell’s inequality will be broken, allowing for a larger correlation than would normally be feasible.

# Experiments With The Entangled States And Violation Of Bell’s Inequality

In order to study and manipulate particles in entangled states for different applications and discoveries, the three Nobel laureates conducted extraordinary and ground-breaking experiments.

John Clauser, Michael Horne, Abner Shimony, and Richard Holt (CHSH) began exploring Bell’s inequality in 1968 by using a variant of the EPR thought experiment. He sent the entangled photons in opposite directions to filters that let only one orientation of polarized photons through. In this modified version of the experiment, he found out that under certain conditions measurements violate Bell’s inequality and were showing a stronger correlation. He then went on to conduct another experiment, with Stuart Freedman, where they showed the result was a clear violation of a Bell inequality and agreed with the predictions of quantum mechanics.

While Clauser and other physicists were successful in showing that Bell’s inequality was broken, their experiments had flaws. For instance, Bell inequalities assume that the two entangled particles’ measurements are completely independent of one another and at random. However, because Clauser’s experiment used filters with predetermined angles, it was known beforehand whether or not photons of a given polarization would get through, hence the measurements were not completely random and independent. Alain Aspect, along with his collaborators Phillipe Grangier, Gérard Roger, and Jean Dalibard, planned a series of tests to plug the hole, employing refined methods and cutting-edge apparatus. When comparing his results to the Freedman-Clauser experiment’s results, which were only accurate to within six standard deviations, his breach of the Bell inequality stands out as particularly striking. To further guarantee the accuracy of the results, Aspect used random polarization settings for the photons as they traveled between the detectors.

The phenomena of quantum entanglement have quickly risen to the forefront of the new and exciting area of quantum information research. Multiple significant advances have been made since then in utilizing these entangled photons for their full potential. Anton Zeilinger started looking into the basics of quantum entanglement and its potential uses. The no-cloning theorem states that it is impossible to produce an independent and identical duplicate of any unknown quantum state. But an experiment conducted by Zeilinger and Francesco De Martini proved that teleporting a quantum state from one location to another is achievable; the only requirement is that the original copy be destroyed. In fact, Zeilinger and his group demonstrated that teleportation can occur over a distance of 144 kilometers between the two Canary Islands. He also showed that entangled photons can also be teleported, a phenomenon he called “Entanglement Swapping”. Recent advances in quantum computing are profoundly influenced by both of these phenomena. Moreover, Zeilinger heavily contributed to the field of multi-particle entanglement. Together with Daniel Greenberger and Michael Horne, he showed for the first time that entanglement can involve more than two particles in an experiment (GHZ theorem). Anton Zeilinger’s lab has contributed significantly to the development of novel entangled states and quantum cryptography.

# A New Era Of Quantum Technology

These studies and findings have paved the way for further investigation into quantum technologies like quantum computers, quantum networks, and quantum encrypted communication. Entangled photons are made to commute between large distances, as far as the distance between a satellite in space and a station on the earth. Systems with more than two entangled particles are now being experimented with and developed. Quantum computers, which largely depend on quantum entanglement, will be able to do complex computations way faster than classical computers. Secure data transmission may receive a significant boost from quantum cryptography, which has the potential to significantly affect existing cryptographic systems. In order to realize these advancements, many countries and big technology companies are currently investing in quantum computing.

Read about the Nobel Prize 2022 in Physiology or Medicine.

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