Narrowband and high-rate entangled photon-pair generation from a high-Q silicon microring resonator

Entangled photon-pair sources are indispensable building blocks of quantum information processing technologies. Among the available approaches, on-chip microresonators are particularly promising owing to their resonant enhancement, CMOS-compatible fabrication, and wafer-scale integration capabilities. In this study, we optimized the structure of silicon microring resonators to suppress sidewall scattering. As a result, we achieved an intrinsic Q-factor of 1.26$\times$10${}^6$ using only standard fabrication processes. The high-Q resonator enabled a brightness coefficient of 3.9$\times$10${}^9$ Hz/GHz/mW${}^2$, with a maximum brightness of 22.0 MHz/GHz and a maximum photon-pair generation rate of 9.19 MHz. Furthermore, Franson-type two-photon interference exhibited a visibility of 98.0$\pm$0.2%, confirming time-energy entanglement. These results show that narrow bandwidth and high generation rate can be achieved simultaneously in CMOS-compatible silicon photonic sources, advancing their use in quantum repeaters.