Single-pass generation of widely-tunable frequency-domain entangled photon pairs

We demonstrate a novel technique that generates entangled photon pairs in the frequency domain by using a single nonlinear crystal. The technique is based on the simultaneous occurrence of two spontaneous parametric down-conversion processes satisfying independent type-II collinear pseudo-phase matching conditions in periodically poled stoichiometric lithium tantalate. The generated photon pairs exhibit nondegenerate Hong-Ou-Mandel interference, indicating the presence of quantum entanglement in the frequency domain. This method provides a light source capable of wide-range quantum sensing and quantum imaging or high-dimensional quantum processing.