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Physics Encyclopedia Entry 1779493265

** This entry discusses the fundamental principles of **Quantum Entanglement**, a phenomenon in which particles become connected and correlated, exhibiting non-local behavior. ## Overview Quantum Entanglement is a fundamental aspect of **Quantum Mechanics**, the branch of physics that describes the behavior of matter and energy at the smallest scales. It was first proposed by **Albert Einstein** in 1935 as a thought experiment to demonstrate the seemingly absurd implications of **Quantum Mechanics**. However, subsequent experiments have confirmed the existence of entanglement, revealing a fascinating and counterintuitive aspect of the quantum world. At its core, entanglement is a phenomenon in which two or more particles become correlated in such a way that the state of one particle is dependent on the state of the other, even when separated by large distances. This correlation is not due to any physical connection between the particles, but rather a fundamental aspect of the quantum world. Entanglement has been observed in a wide range of systems, from photons to electrons to atoms, and has been used in various applications, including quantum computing and cryptography. ## History/Background The concept of entanglement was first introduced by **Albert Einstein**, **Boris Podolsky**, and **Nathan Rosen** in their 1935 paper "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?" (EPR). They proposed a thought experiment in which two particles, A and B, were created in such a way that their properties were correlated. If the state of particle A was measured, the state of particle B would be instantaneously determined, regardless of the distance between the two particles. This seemed to imply that information was being transmitted faster than the speed of light, violating the principles of **Special Relativity**. However, in 1964, **John Stewart Bell** showed that entanglement was a real phenomenon that could be experimentally verified. He derived a mathematical inequality, now known as Bell's theorem, which showed that if entanglement was real, it would be possible to violate certain statistical constraints. This led to a series of experiments, starting with the work of **Claude Cohen-Tannoudji** and **Gérard Grynberg** in 1972, which confirmed the existence of entanglement. ## Key Information * **Quantum Entanglement** is a fundamental aspect of **Quantum Mechanics**, describing the correlation between particles. * Entanglement is a non-local phenomenon, meaning that the state of one particle is dependent on the state of the other, even when separated by large distances. * Entanglement has been observed in a wide range of systems, including photons, electrons, and atoms. * Entanglement is used in various applications, including **Quantum Computing** and **Quantum Cryptography**. * The EPR paradox, proposed by **Albert Einstein**, **Boris Podolsky**, and **Nathan Rosen**, demonstrated the seemingly absurd implications of entanglement. ## Significance Quantum Entanglement has far-reaching implications for our understanding of the quantum world and its applications. It has been used in various fields, including: * **Quantum Computing**: Entanglement is a key resource for quantum computing, allowing for the creation of quantum gates and the implementation of quantum algorithms. * **Quantum Cryptography**: Entanglement-based cryptography offers secure communication over long distances, using the principles of entanglement to encode and decode messages. * **Quantum Information**: Entanglement is a fundamental aspect of quantum information theory, describing the correlation between particles and the principles of quantum measurement. INFOBOX: - **Name:** Quantum Entanglement - **Type:** Quantum Phenomenon - **Date:** 1935 (EPR paradox), 1964 (Bell's theorem), 1972 (first experimental confirmation) - **Location:** Theoretical, with experimental verification in various laboratories - **Known For:** The fundamental aspect of **Quantum Mechanics**, describing the correlation between particles. TAGS: **Quantum Mechanics**, **Quantum Entanglement**, **EPR Paradox**, **Bell's Theorem**, **Quantum Computing**, **Quantum Cryptography**, **Quantum Information**, **Non-Locality**.