Simple explanation of the quantum violation of a fundamental inequality

TL;DR

This paper demonstrates that the maximum quantum violation of the KCBS inequality aligns with a principle called global exclusivity, which constrains probabilities of pairwise exclusive events, providing insights into quantum contextuality and ruling out nonlocal boxes.

Contribution

It introduces the principle of global exclusivity as a fundamental explanation for quantum violations of the KCBS inequality and related nonlocality constraints.

Findings

Maximum quantum violation equals the limit set by global exclusivity.

Global exclusivity singles out quantum contextuality scenarios.

The principle excludes the existence of nonlocal boxes.

Abstract

We show that the maximum quantum violation of the Klyachko-Can-Binicioglu-Shumovsky (KCBS) inequality is exactly the maximum value satisfying the following principle: The sum of probabilities of pairwise exclusive events cannot exceed 1. We call this principle "global exclusivity," since its power shows up when it is applied to global events resulting from enlarged scenarios in which the events in the inequality are considered jointly with other events. We identify scenarios in which this principle singles out quantum contextuality, and show that a recent proof excluding nonlocal boxes follows from the maximum violation imposed by this principle to the KCBS inequality.