Bell measurement rules out supraquantum correlations

TL;DR

This paper demonstrates that adding a specific global measurement to non-signaling boxes restricts their correlations to those allowed by quantum mechanics, effectively ruling out stronger supraquantum correlations.

Contribution

The authors introduce a global measurement in non-signaling boxes that, when combined with existing constraints, limits correlations to quantum levels, bridging non-signaling theories and quantum mechanics.

Findings

Global measurement rules out supraquantum correlations

System admits only quantum correlations of two qubits

Interpolation between quantum and no-signaling theories achieved

Abstract

The so called bipartite non-signaling boxes are systems whose statistics is constrained solely by the principle of no instantaneous signaling between distant locations. Such systems can exhibit much stronger correlations than those admitted by quantum mechanics. Inspired by quantum logic approach of Tylec and Ku\'{s}, J. Phys. A: Math. Theor. 48 (2015) 505303, we consider non-signaling boxes with three inputs per party, and extend the set of measurements with just a single {\it global} measurement - one that mimics quantum two-party Bell measurement. We then show that this seemingly mild extension completely rules out supraquantum correlations: the resulting system admits precisely quantum mechanical correlations of two qubits. We also consider non-maximally entangled measurements, obtaining interpolation between quantum and full no-signaling theory. Our study paves a way to a general programme of amending no-signaling theories with some measurements inherited from quantum mechanics, leading to various interpolations between non-signaling boxes and quantum mechanics.