Theoretical Investigation of a Spectrally Pure-State Generation from Isomorphs of KDP Crystal at Near-Infrared and Telecom Wavelengths

In photonic quantum information processing, spectrally uncorrelated biphoton states generated from nonlinear crystals are a fundamental resource, but a rare one, and researchers have only used a few kinds of crystals to produce such biphoton states, over a limited wavelength range. This study reveals that crystals of a family of phosphate and arsenate salts similar to potassium dihydrogen phosphate (KDP) can be used to generate spectrally pure (as high as 98%) states from near-infrared to telecommunication wavelengths. The key is to engineer group-velocity matching.