An Optimal Polarization-Entanglement Source: Frequency-Converted SPDC with Degeneracy, Indistinguishability, and Ultra-High Purity Configurable Over a Large Spectral Range

TL;DR

This paper introduces a novel SPDC technique that produces high-purity, indistinguishable, and degenerate polarization-entangled photon pairs across a broad spectral range, enhancing quantum networking capabilities.

Contribution

The authors develop a new SPDC method that overcomes phase-matching trade-offs, achieving near-perfect entanglement properties at any visible or NIR wavelength.

Findings

Achieves >99% spectral purity of entangled photons

Provides degeneracy and indistinguishability across a large spectral range

Enables generation of optimal polarization-entangled states for quantum networks

Abstract

Modeling and simulations of entanglement-based quantum-networking protocols commonly assume perfect entangled states. Some investigations have been performed which show how imperfections cause the efficiency of the protocols to rapidly deteriorate. For polarization-entangled states created by SPDC, the fundamentals of phase matching lead to a trade-off problem for the optimal properties of the state. We present a new SPDC method which circumvents the trade-off problem and allows one to obtain degeneracy, indistinguishability, and heralded-single-photon spectral purity greater than 99% for any target SPDC wavelength in the visible and NIR spectrum. Therefore, our method can in principle generate optimal polarization-entangled states for polarization-entanglement-based quantum-networking protocols.