Linear-optical test of quantum contextuality with sequential measurements

TL;DR

This paper presents a linear-optical experimental setup demonstrating quantum contextuality through violation of the KCBS inequality using sequential measurements on single photons, highlighting nonclassical behavior.

Contribution

The authors propose and experimentally implement a linear-optical scheme for testing quantum contextuality with sequential measurements, ensuring consistent physical operations across contexts.

Findings

Successful violation of the KCBS inequality with single photons

Demonstrated robustness against photon loss

Provided a practical tool for probing non-classicality and verifying single-photon sources

Abstract

Quantum contextuality provides a fundamental signature of nonclassical behavior that cannot be explained by noncontextual hidden-variable models. We propose and experimentally implement a linear-optical setup for demonstrating Kochen-Specker contextuality via a violation of the KCBS inequality using single photons. Our scheme employs sequential measurements realized with linear-optical networks and on-off photodetectors. The construction ensures that each co-measured observable is implemented by the same physical operation across different contexts. Our experimental results demonstrate a clear violation of the KCBS inequality and robustness against photon loss. Beyond fundamental investigations, the proposed setup provides a practical tool for probing non-classicality and photon-number statistics of quantum states, which in turn enables the verification of single-photon sources.