Leggett inequality

Leggett inequality

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The Leggett inequalities, named for Anthony James Leggett
Anthony James Leggett
Sir Anthony James Leggett, KBE, FRS , aka Tony Leggett, has been a Professor of Physics at the University of Illinois at Urbana-Champaign since 1983....

, who derived them, are a related pair of mathematical expressions concerning the correlations of properties of entangled
Quantum entanglement
Quantum entanglement occurs when electrons, molecules even as large as "buckyballs", photons, etc., interact physically and then become separated; the type of interaction is such that each resulting member of a pair is properly described by the same quantum mechanical description , which is...

 particles. (As published by Leggett, the inequalities were exemplified in terms of relative angles of elliptical and linear polarizations.) They are fulfilled by a large class of physical theories based on particular non-local
Nonlocality
In Classical physics, nonlocality is the direct influence of one object on another, distant object. In Quantum mechanics, nonlocality refers to the absence of a local, realist model in agreement with quantum mechanical predictions.Nonlocality may refer to:...

 and realistic
Philosophical realism
Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....

 assumptions, that may be considered to be plausible or intuitive according to common physical reasoning.

The Leggett inequalities are violated by quantum mechanical theory
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

. The results of experimental tests in 2007 and 2010 have shown agreement with quantum mechanics rather than the Leggett inequalities.

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