Conditions for the compatibility of channels in general probabilistic theory and their connection to steering and Bell nonlocality

TL;DR

This paper establishes general conditions for channel compatibility in probabilistic theories, linking them to steering and Bell nonlocality, and explores their implications in quantum theory with numerous examples.

Contribution

It introduces a formalism for channel steering and Bell nonlocality as entanglement-assisted incompatibility tests, extending concepts beyond measurements.

Findings

Steering is not necessary for Bell nonlocality in quantum channels.

All measurement-based definitions are recovered as special cases.

Many examples illustrate the new concepts and their implications.

Abstract

We derive general conditions for the compatibility of channels in general probabilistic theory. We introduce formalism that allows us to easily formulate steering by channels and Bell nonlocality of channels as generalizations of the well-known concepts of steering by measurements and Bell nonlocality of measurements. The generalization does not follow the standard line of thinking stemming from the Einstein-Podolsky-Rosen paradox, but introduces steering and Bell nonlocality as entanglement-assisted incompatibility tests. We show that all of the proposed definitions are, in the special case of measurements, the same as the standard definitions, but not all of the known results for measurements generalize to channels. For example, we show that for quantum channels, steering is not a necessary condition for Bell nonlocality. We further investigate the introduced conditions and concepts in the special case of quantum theory and we provide many examples to demonstrate these concepts and their implications.