Quantum nonlocality
In theoretical physics, Quantum nonlocality refers to the phenomenon by which the measurement statistics of a multipartite quantum system do not allow an interpretation with local realism. Quantum nonlocality has been experimentally verified under a variety of physical assumptions.
Quantum nonlocality does not allow for faster-than-light communication, and hence is compatible with special relativity and its universal speed limit of objects. Thus, quantum theory is local in the strict sense defined by special relativity and, as such, the term “quantum nonlocality” is sometimes considered a misnomer. Still, it prompts many of the foundational discussions concerning quantum theory.
Quantum nonlocality is the phenomenon where entangled particles become permanently correlated, meaning a measurement on one particle instantaneously influences the state of another, regardless of the distance between them. This “spooky action-at-a-distance” violates the classical principle of locality but does not allow for faster-than-light communication. John Stewart Bell’s theorem provided a framework for experimentally verifying nonlocality, with tests by Clauser and Aspect confirming its existence. Nonlocality is a fundamental resource in quantum information science and technologies like quantum cryptography and secure communication.
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What is it?
- Entanglement: Quantum nonlocality is a consequence of quantum entanglement, a state where two or more particles are linked in such a way that they share the same fate.
- Instantaneous Correlation: When entangled particles are separated, a measurement performed on one particle instantly determines the state of the other, no matter how far apart they are.
- Violation of Locality: Classical physics assumes locality, meaning that effects can only propagate at or below the speed of light through physical connections. Nonlocality challenges this by demonstrating correlations that appear to happen faster than light.
Key Concepts
- Bell’s Theorem: In 1964, John Stewart Bell established an inequality that any theory based on local hidden variables would have to satisfy.
- Experimental Verification: Experiments by John Clauser and Alain Aspect in the 1970s and 1980s demonstrated that quantum mechanical predictions, which violate Bell’s inequality, are correct, proving nonlocality is a real phenomenon.
- No Faster-Than-Light Communication: Despite the instantaneous correlation, quantum nonlocality does not permit sending information faster than light. This is because the outcomes of the measurements are random, and while they are correlated, one observer cannot control the outcome of the other’s measurement to send a specific message.
Why is it important?
- Fundamental Quantum Property: Quantum nonlocality reveals the deeply interconnected and non-intuitive nature of the quantum world.
- Technology: It serves as a vital resource for advanced technologies, including secure communication, quantum cryptography, and the certification of random numbers.
AI responses may include mistakes.
[1] https://quantumphysicslady.org/glossary/quantum-nonlocality/
[2] https://www.sciencedirect.com/topics/physics-and-astronomy/quantum-nonlocality
[3] wikipedia/en/Quantum_nonlocality
[5] https://dst.gov.in/new-study-quantum-nonlocality-expands-scope-its-use
[12] https://www.ncts.ncku.edu.tw/phys/qis/151210/
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