The operational no-signalling constraints and their implications

TL;DR

This paper develops a unified operational no-signalling framework to analyze quantum correlations in relativistic spacetimes, revealing implications for causality, symmetry, and black hole physics.

Contribution

It introduces a comprehensive framework for studying nonlocal and temporal correlations in relativistic contexts, challenging recent claims about causal loops and superluminal signalling.

Findings

Violation of no-signalling implies paradoxes or symmetry violations in Minkowski spacetime.

Jamming of nonlocal correlations can occur without violating no-signalling constraints.

Black hole spacetimes allow jamming of correlations across the event horizon without causality issues.

Abstract

The study of quantum correlations within relativistic spacetimes, and the consequences of relativistic causality on information processing using such correlations, has gained much attention in recent years. In this paper, we establish a unified framework in the form of operational no-signalling constraints to study both nonlocal and temporal correlations within general relativistic spacetimes. We explore several intriguing consequences arising from our framework. Firstly, we show that the violation of the operational no-signalling constraints in Minkowski spacetime implies either a logical paradox or an operational infringement of Poincar\'{e} symmetry. We thereby examine and subvert recent claims in [Phys. Rev. Lett. 129, 110401 (2022)] on the possibility of witnessing operationally detectable causal loops in Minkowski spacetime. Secondly, we explore the possibility of jamming of nonlocal correlations, controverting a recent claim in [Nat. Comm. 16, 269 (2025)] that a physical mechanism for jamming would necessarily lead to superluminal signalling. Finally, we show that in black hole spacetimes certain nonlocal correlations under and across the event horizon can be jammed by any agent without spoiling the operational no-signalling constraints.