Properties of entangled photon pairs generated by a CW laser with small coherence time: theory and experiment

TL;DR

This paper investigates how the coherence time of a continuous-wave laser affects the quality of entangled photon pairs generated via parametric down-conversion, combining theoretical analysis and experimental validation.

Contribution

It presents a comprehensive model and experimental verification of entangled photon generation using a compact setup with small coherence time lasers, including effects on entanglement quality and Bell inequality violation.

Findings

Coherence time influences entanglement visibility.

Bell inequality violation depends on crystal length.

Quantum tomography confirms the theoretical model.

Abstract

The generation of entangled photon pairs by parametric down--conversion from solid state CW lasers with small coherence time is theoretically and experimentally analyzed. We consider a compact and low-cost setup based on a two-crystal scheme with Type-I phase matching. We study the effect of the pump coherence time over the entangled state visibility and over the violation of Bell's inequality, as a function of the crystals length. The full density matrix is reconstructed by quantum tomography. The proposed theoretical model is verified using a purification protocol based on a compensation crystal.