Contextuality, Complementarity, Signaling, and Bell tests

TL;DR

This review explores the interplay between contextuality, complementarity, and signaling in quantum mechanics, emphasizing how Bell inequalities serve as tests for contextuality and how signaling affects these tests.

Contribution

It clarifies the relationship between contextuality and Bell inequalities, introduces the concept of signaling in experimental data, and discusses the framework of Contextuality by Default (CbD).

Findings

Bell inequalities test for joint measurement contextuality.

Signaling can be an experimental artifact or an intrinsic feature.

Bell-Dzhafarov-Kujala inequalities quantify signaling effects.

Abstract

This is a review devoted to the complementarity-contextuality interplay with connection to the Bell inequalities. Starting discussion with complementarity, we point out to contextuality as its seed. {\it Bohr-contextuality} is dependence of observable's outcome on the experimental context, on system-apparatus interaction. Probabilistically, complementarity means that the {\it joint probability distribution} (JPD) does not exist. Instead of the JPD, one has to operate with contextual probabilities. The Bell inequalities are interpreted as the statistical tests of contextuality and, hence, incompatibility. For context dependent probabilities, these inequalities may be violated. We stress that contextuality tested by the Bell inequalities is so called {\it joint measurement contextualit}y (JMC), the special case of Bohr's contextuality. Then, we examine the role of signaling (marginal inconsistency). In QM, signaling can be considered as an experimental artifact. However, often experimental data has signaling patterns. We discuss possible sources of signaling; for example, dependence of the state preparation on measurement settings. In principle, one can extract the measure of "pure contextualize" from data shadowed by signaling. This theory known as {\it Contextuality by Default} (CbD). It leads to inequalities with the additional term quantifying signaling, Bell-Dzhafarov-Kujala inequalities.