The ideal photon-pair source for building up multi-qubit states needs to produce indistinguishable photons with high efficiency. Indistinguishability is crucial for minimising errors in two-photon interference, central to building larger states, while high heralding rates will be needed to overcome unfavourable loss scaling. Domain engineering in parametric down-conversion sources negates the need for lossy spectral filtering allowing one to satisfy these conditions inherently within the source design. Here, we present a telecom-wavelength parametric down-conversion photon source that operates on the achievable limit of domain engineering. We generate photons from independent sources which achieve two-photon interference visibilities of up to 98.6±1.1% without narrow-band filtering. As a consequence, we reach net heralding efficiencies of up to 67.5%, which corresponds to collection efficiencies exceeding 90%.
@article{arxiv.2101.08280,
title = {Optimised Domain-engineered Crystals for Pure Telecom Photon Sources},
author = {Alexander Pickston and Francesco Graffitti and Peter Barrow and Christopher Morrison and Joseph Ho and Agata M. Brańczyk and Alessandro Fedrizzi},
journal= {arXiv preprint arXiv:2101.08280},
year = {2021}
}