Bell test

An experiment that measures correlations between separated outcomes and tests whether they satisfy Bell inequalities. Violations rule out local hidden-variable theories under specified assumptions.

Bell inequality: A mathematical bound on correlations predicted by local hidden-variable theories under specified assumptions. A Bell test compares observed correlations with this bound.
John Stewart Bell: A Northern Irish physicist who derived inequalities constraining correlations in local hidden-variable theories. His 1964 theorem made the experimental distinction precise.
Freedman–Clauser experiment: A 1972 photon-correlation experiment that found a violation of a Bell inequality. It was the first influential experimental violation of a Bell inequality.
Local realism: A worldview combining locality with the idea that physical properties have definite values independent of measurement. Bell violations conflict with theories satisfying the assumptions commonly grouped under this label.
Bell state: A maximally entangled quantum state of two subsystems with correlations that cannot be explained by local hidden-variable theories. Bell tests often measure pairs prepared in these entangled states.
EPR paradox: A 1935 argument that quantum mechanics might be incomplete because it predicts distant correlations between entangled systems. Bell tests address the challenge to quantum completeness raised by this argument.
Aspect's Bell test experiments: A series of 1980s photon experiments by Alain Aspect and colleagues testing Bell inequalities with rapidly switched analyzers. The experiments addressed whether measurement settings could be coordinated through ordinary signals.
Nonlocal hidden-variable theory: A hidden-variable theory that permits influences or dependencies incompatible with relativistic locality. Bell violations exclude local hidden variables, not every hidden-variable account.
Quantum entanglement: A quantum relation in which multiple systems share a state that cannot be described as independent states. Entanglement supplies the correlations that can violate Bell inequalities.
Hidden-variable theory: A class of theories supplementing quantum mechanics with variables intended to account for measurement outcomes. Bell's inequality tests constrain the local versions of these theories.

Linked from 18 pages