Spectrally multiplexed and bright entangled photon pairs in a lithium niobate microresonator

On-chip bright quantum sources with multiplexing ability are extremely high in demand for integrated quantum networks with unprecedented scalability and complexity. Here, we demonstrate a bright and broadband biphoton quantum source with spectral multiplexing generated in a lithium niobate microresonator system. Without introducing the conventional domain poling, the on-chip microdisk produces photon pairs covering a broad bandwidth promised by natural phase matching in spontaneous parametric down conversion. Experimentally, the multiplexed photon pairs are characterized by 30 nm bandwidth limited by the filtering system, providing over 40 multiplexing channels with a 0.8 nm channel spacing. Meanwhile, the generation rate reaches 5.13 MHz/µW with a coincidence-to-accidental ratio up to 804, and the quantum source manifests a high purity with a heralded single photon correlation g_H⁽²⁾(0) = 0.0098 ± 0.0021. Furthermore, the energy-time entanglement is demonstrated with an excellent interference visibility of 96.5% ± 2%. Such a quantum source at the telecommunication band paves the way for high-dimensional entanglement and future integrated quantum information systems.