Independent high-purity photons created in domain-engineered crystals

Advanced photonic quantum technology relies on multiphoton interference, which requires bright sources of high-purity photons. Single-photon sources based on nonlinear parametric processes typically require lossy spectral filtering for enhancing the spectral purity of the heralded photons. Here, we implement a novel domain-engineering technique for tailoring the nonlinearity of a parametric down-conversion crystal in order to generate indistinguishable and spectrally pure photons without filtering. We create pairs of independently heralded telecom-wavelength photons with high heralding efficiency (up to 65%) and brightness (4 kHz/mW), and we demonstrate a high lower bound for the indistinguishability (98.7 +/- 0.2%) and spectral purity (90.7 +/- 0.3%) via two-photon interference experiments. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.