Optimizing type-I polarization-entangled photons

TL;DR

This paper presents methods to optimize type-I polarization-entangled photon sources, achieving high fidelity and brightness by using compensation techniques and novel crystal materials, advancing quantum information processing capabilities.

Contribution

It introduces combined compensation techniques and the first polarization-entanglement from BiBO crystals, significantly improving source quality and brightness.

Findings

Over 400-fold improvement in phase flatness with spatial compensation

Achieved 99% fidelity in ultrafast polarization-entanglement

First demonstration of polarization-entanglement from BiBO crystal

Abstract

Optical quantum information processing needs ultra-bright sources of entangled photons, especially from synchronizable femtosecond lasers and low-cost cw-diode lasers. Decoherence due to timing information and spatial mode-dependent phase has traditionally limited the brightness of such sources. We report on a variety of methods to optimize type-I polarization-entangled sources - the combined use of different compensation techniques to engineer high-fidelity pulsed and cw-diode laser-pumped sources, as well as the first production of polarization-entanglement directly from the highly nonlinear biaxial crystal BiB3O6 (BiBO). Using spatial compensation, we show more than a 400-fold improvement in the phase flatness, which otherwise limits efficient collection of entangled photons from BiBO, and report the highest fidelity to date (99%) of any ultrafast polarization-entanglement source. Our numerical code, available on our website, can design optimal compensation crystals and simulate entanglement from a variety of type-I phasematched nonlinear crystals.