Single-photon quantum nonlocality: Violation of the Clauser-Horne-Shimony-Holt inequality using feasible measurement setups

TL;DR

This paper demonstrates that single-photon quantum nonlocality can be observed using feasible measurement setups involving on-off and homodyne detections, with maximal violation of the CHSH inequality achieved through squeezed-and-displaced on-off measurements.

Contribution

It introduces a practical measurement scheme for detecting single-photon nonlocality and shows its robustness against experimental imperfections.

Findings

Single-photon nonlocality detected with up to two homodyne detections.

Maximum CHSH violation achieved with squeezed-and-displaced on-off measurements.

Squeezed-and-displaced schemes outperform displacement-only measurements under imperfections.

Abstract

We investigate quantum nonlocality of a single-photon entangled state under feasible measurement techniques consisting of on-off and homodyne detections along with unitary operations of displacement and squeezing. We test for a potential violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality, in which each of the bipartite party has a freedom to choose between 2 measurement settings, each measurement yielding a binary outcome. We find that single-photon quantum nonlocality can be detected when two or less of the 4 total measurements are carried out by homodyne detection. The largest violation of the CHSH inequality is obtained when all four measurements are squeezed-and-displaced on-off detections. We test robustness of violations against imperfections in on-off detectors and single-photon sources, finding that the squeezed-and-displaced measurement schemes perform better than the displacement-only measurement schemes.