Consistency and Causality of Interconnected Nonsignaling Resources

TL;DR

This paper develops a framework for analyzing networks of nonsignaling resources shared among parties, establishing their joint distributions, causality, and extremal properties, with applications to nonlocality inequalities.

Contribution

It introduces a formal framework for interconnected nonsignaling resources, proving joint distribution uniqueness, causality, and the sufficiency of extremal resources in such networks.

Findings

Joint distribution for shared resources is uniquely determined and nonsignaling.

Considering extremal nonsignaling resources suffices for analyzing network properties.

The framework supports the causal interpretation of nonsignaling boxes and local wirings.

Abstract

This paper examines networks of $n$ measuring parties sharing $m$ nonsignaling resources that can be locally wired together: that is, each party follows a scheme to measure the resources in a cascaded fashion with inputs to later resources possibly depending on outputs of earlier-measured ones. A specific framework is provided for studying probability distributions arising in such networks, and this framework is used to directly prove some accepted, but often only implicitly invoked, facts: there is a uniquely determined and well-defined joint probability distribution for the outputs of all resources shared by the parties, and this joint distribution is nonsignaling. It is furthermore shown that is often sufficient to restrict consideration to only extremal nonsignaling resources when considering features and properties of such networks. Finally, the framework illustrates how the physical theory of nonsignaling boxes and local wirings is causal, supporting the applicability of the inflation technique to constrain such models. For an application, we probe the example of (3,2,2) inequalities that witness genuine three-party nonlocality according to the local-operations-shared-randomness definition, and show how all other examples can be derived from that of Mao et al. [Phys. Rev. Lett. 129:150401 (2022)]