Testing Single Photon Entanglement using Self-Referential Measurements

TL;DR

This paper demonstrates a novel method to test single-photon entanglement by using self-referential measurements on two copies of the state, avoiding complex homodyne setups and potential loopholes.

Contribution

It introduces an alternative experimental approach to violate Bell inequalities with single photons using joint measurements on identical copies, simplifying the process.

Findings

Achieved CHSH parameters of 2.71 and 2.23, confirming violation of Bell inequality.

Implemented a self-referential measurement scheme that avoids homodyne detection.

Provides a more accessible method for testing single-photon nonlocality.

Abstract

Entanglement does not always require one particle per party. It was predicted some thirty years ago that a single photon traversing a beam splitter could violate a Bell inequality. Although initially debated, single-photon nonlocality was eventually demonstrated via homodyne measurements. Here, we present an alternate realisation that avoids the complexity of homodyne measurements and potential loopholes in their implementation. We violate a Bell inequality by performing joint measurements on two copies of the same single-photon entangled state, where one photon acts as a phase reference for the other, making it self-referential. We observe CHSH parameters of $2.71\pm 0.09$ and $2.23\pm 0.07$, depending on the joint measurements implemented. This offers a new perspective on single-photon nonlocality and a more accessible experimental route, potentially applicable to general mode-entangled states in diverse platforms.