Single-Photon Nonlinearity from a Nanobeam with a Quantum Dot.

Optical nonlinearity at the single-photon level enables strong interactions between individual photons. Such single-photon nonlinearity underlies key applications including photon–photon logic operations, quantum information processing, and the generation of nonclassical light. Semiconductor quantum dots coupled to photonic crystal cavities offer an attractive platform for realizing photonic nonlinearity, as the cavity enhances light–matter interactions by confining light within a subwavelength volume. We demonstrate single-photon nonlinearity from a nanobeam photonic crystal cavity coupled to a single quantum dot. With a high-quality factor and very small mode volume of the cavity, we achieved strong quantum dot–cavity coupling with a cooperativity of 9. The nanobeam incorporates a tapered edge that enables efficient direct coupling to a single-mode optical fiber, achieving a maximum nanobeam-to-fiber coupling efficiency of 60%. We observe a large reflectivity contrast and clear photon antibunching in the reflected signal, showing efficient light–matter interactions at the single-photon level. This single-photon nonlinearity in a nanobeam cavity serves as a robust and scalable platform for photonic quantum technologies.