Compact Polarization-Entangled Photon Source Based on Coexisting Noncritically Birefringent and Quasi Phase Matching in a Nonlinear Crystal

TL;DR

This paper introduces a compact, high-fidelity polarization-entangled photon source using coexisting phase-matching techniques in a nonlinear crystal, suitable for scalable quantum technologies.

Contribution

It demonstrates a novel photon source that combines noncritical birefringent and quasi phase matching in a single crystal, eliminating complex alignment and post-processing.

Findings

Photon pairs with fidelity 0.998 and concurrence 0.935.

Violates CHSH inequality by 84 standard deviations.

Compact, scalable source suitable for quantum computing and communication.

Abstract

Polarization-entangled photons are indispensable to numerous quantum technologies and fundamental studies. In this paper, we propose and demonstrate a novel source that generates collinear polarization-entangled photons by simultaneously achieving two distinct types of phase-matching conditions (noncritically birefringent and quasi phase matching) in a periodically poled nonlinear crystal with a large poling period of 2 mm. The photon pairs are generated in a polarization-entangled state with a fidelity and concurrence of 0.998 and 0.935, respectively, and violate the Clauser-Horne-Shimony-Holt inequality by 84 standard deviations. The compact source does not require interferometer, delicate domain structures, or post selection, and is advantageous for scalable quantum computing and communication, where many replicas or chip-scale devices are needed.