Information causality in multipartite scenarios

The Bell nonlocality is one of the most intriguing and counterintuitive phenomena displayed by quantum systems. Interestingly, such stronger-than-classical quantum correlations are somehow constrained, and one important question to the foundations of quantum theory is whether there is a physical, operational principle responsible for those constraints. One candidate is the information causality principle, which, in some particular cases, is proven to hold for quantum systems and to be violated by stronger-than-quantum correlations. In multipartite scenarios, though, it is known that the original formulation of the information causality principle fails to detect even extremal stronger-than-quantum correlations, thus suggesting that a genuinely multipartite formulation of the principle is necessary. In this work, we advance towards this goal, reporting a different formu-lation of the information causality principle in multipartite scenarios. By proposing a change of perspective, we obtain multipartite informational inequalities that work as necessary criteria for the principle to hold. We prove that such inequalities hold for all quantum resources and forbid some stronger-than-quantum ones. Finally, we show that our approach can be strengthened if multiple copies of the resource are available, or, counterintuitively, if noisy communication channels are employed.

Automated summary

Bell nonlocality is a fascinating and counterintuitive phenomenon exhibited by quantum systems. The information causality principle is a potential explanation for the constraints on stronger-than-quantum correlations. However, the original formulation of this principle fails to detect even extreme stronger-than-quantum correlations in multipartite scenarios, indicating the need for a genuinely multipartite formulation. In this study, we propose a new formulation of the information causality principle in multipartite scenarios, introducing multipartite informational inequalities as necessary criteria for the principle to hold. We prove that these inequalities hold for all quantum resources and forbid some stronger-than-quantum ones. Furthermore, our approach can be strengthened with multiple copies of the resource or the use of noisy communication channels.