CHSH inequality

<p>In <a href="/facts/Physics/a7aH2y08">physics</a>, the Clauser–Horne–Shimony–Holt (CHSH) inequality can be used in the proof of <a href="/facts/Bell%2527s_theorem/lg1V6kpk">Bell's theorem</a>, which states that certain consequences of <a href="/facts/Quantum_entanglement/afzslwN0">entanglement</a> in <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a> cannot be reproduced by <a href="/facts/Local_hidden-variable_theory/wXo2mmvp">local hidden-variable theories</a>. Experimental verification of the inequality being violated is seen as <a href="/facts/Experimental_confirmation/182j8RWE">confirmation</a> that nature cannot be described by such theories. CHSH stands for <a href="/facts/John_Clauser/o6CjMy76">John Clauser</a>, <a href="/facts/Michael_Horne_(physicist)/2l2RtuDh">Michael Horne</a>, <a href="/facts/Abner_Shimony/x2NjV8p1">Abner Shimony</a>, and Richard Holt, who described it in a much-cited paper published in 1969. They derived the CHSH inequality, which, as with <a href="/facts/John_Stewart_Bell/vsrqUAX3">John Stewart Bell</a>'s original inequality, is a constraint—on the statistical occurrence of coincidences in a <a href="/facts/Bell_test/YDKYlhGa">Bell test</a>—which is necessarily true if an underlying <a href="/facts/Local_hidden-variable_theory/wXo2mmvp">local hidden-variable theory</a> exists. In practice, the inequality is routinely violated by modern experiments in quantum mechanics.
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CHSH inequality open-in-new

CHSH inequality