Versatile on-chip reconfigurable two-photon interference platforms using thin-film lithium niobate

Integrated quantum photonic technologies require scalable devices with high-visibility quantum interference. Recent studies have demonstrated that lithium niobate on insulator enables efficient nonlinear interactions, via quasi-phase matching in periodically poled lithium niobate (PPLN) waveguides. However, the on-chip control of two-photon interference utilizing path entanglement remains limited. In this study, we demonstrate on-chip generation of single-photon sources via quantum interference using path-entangled N00N states in two ways. Using the basic structure of a reverse Hong–Ou–Mandel (RHOM) configuration, we directly observe high on-chip visibility of quantum interference. We achieve a visibility of 97.7% ± 1.1% using a dual-PPLN waveguide as the basic RHOM configuration. To improve the compactness, efficiency, and stability of on-chip operation, we further incorporate a PPLN ring resonator with a Sagnac loop. This allows counter-propagating paths to share a single periodically poled waveguide, achieving a visibility of 84.4% ± 1.6%. These results demonstrate that lithium niobate on insulator (LNOI)-based quantum photonic systems provide a robust foundation for the development of future integrated quantum technologies.