From contextuality of a single photon to realism of an electromagnetic wave

TL;DR

This paper argues that classical light experiments cannot violate Bell inequalities because they measure field intensities, which differ fundamentally from single-photon detections used in genuine quantum Bell tests, thus reaffirming the non-classicality indicator.

Contribution

It clarifies that classical light experiments cannot truly violate Bell inequalities due to measurement differences, reinforcing the significance of single-photon detection in quantum non-locality tests.

Findings

Classical light experiments do not violate Bell inequalities.

Field intensity measurements differ fundamentally from single-photon detections.

Classical bounds of Bell inequalities are shifted to algebraic limits in classical experiments.

Abstract

Violations of Bell inequalities have been an incontestable indicator of non-classicality since the seminal paper by John Bell. However, recent claims of Bell inequalities violations with classical light have cast some doubts on their significance as hallmarks of non-classicality. Here, we challenge those claims. The crux of the problem is that such classical experiments simulate quantum probabilities with intensities of classical fields. However, fields intensities measurements are radically different from single-photon detections, which are primitives of any genuine Bell experiment. We show that this fundamental difference between field intensities measurements and single photon detections shifts the classical bound of relevant Bell inequalities to its algebraic limit, leaving no place for their violations.