Phase-stable source of high-quality three-photon polarization entanglement by cascaded downconversion

TL;DR

This paper introduces a fully phase-stable, high-fidelity three-photon polarization entanglement source using cascaded downconversion, enhancing robustness and usability for quantum communication applications.

Contribution

The authors develop a novel, phase-stable three-photon entanglement source based on cascaded Sagnac configurations, eliminating the need for active phase stabilization.

Findings

Achieved over 96% fidelity with GHZ state

Demonstrated stability over several days without optimization

Produced high-quality three-photon entangled states

Abstract

Stable sources of entangled photons are important requirements for quantum communications. In recent years, cascaded downconversion has been demonstrated as an effective method of directly producing three-photon entanglement. However, to produce polarization entanglement these sources have until now relied on intricate active phase stabilization schemes, thus limiting their robustness and usability. In this work, we present a completely phase-stable source of three-photon entanglement in the polarization degree of freedom. With this source, which is based on a cascade of two pair sources based on Sagnac configurations, we produce states with over 96\% fidelity with an ideal GHZ state. Moreover, we demonstrate the stability of the source over several days without any ongoing optimization. We expect this source to be a useful tool for applications requiring multiphoton entanglement, such as quantum secret sharing and producing heralded entangled photon pairs.