Measurement sharpness cuts nonlocality and contextuality in every physical theory

TL;DR

This paper proposes a fundamental principle of measurement sharpness that constrains nonlocality and contextuality in all physical theories, aligning their violations with quantum limits and supporting recent foundational principles.

Contribution

It introduces a measurement sharpness postulate that limits nonlocality and contextuality, providing a unifying constraint across physical theories and supporting principles like Local Orthogonality.

Findings

Reduces Bell and Kocher-Specker inequality violations to near quantum levels.

Supports the principles of Local Orthogonality and Consistent Exclusivity.

Provides a fundamental motivation for quantum bounds on nonlocality.

Abstract

Gathering data through measurements is at the basis of every experimental science. Ideally, measurements should be repeatable and, when extracting only coarse-grained data, they should allow the experimenter to retrieve the finer details at a later time. However, in practice most measurements appear to be noisy. Here we postulate that, despite the imperfections observed in real life experiments, there exists a fundamental level where all measurements are ideal. Combined with the requirement that ideal measurements remain so when coarse-grained or applied in parallel on spacelike separated systems, our postulate places a powerful constraint on the amount of nonlocality and contextuality that can be found in an arbitrary physical theory, bringing down the violation of Bell and Kocher-Specker inequalities near to its quantum value. In addition, it provides a new compelling motivation for the principles of Local Orthogonality and Consistent Exclusivity, recently proposed for the characterization of the quantum set of probability distributions.