Single-photon extraction via spatial topological transition

Scalable integrated single-photon sources are critical for quantum photonics and can enable applications such as high-speed quantum communication and quantum information processing. Ideally, to establish a scalable platform, such single-photon sources require emission speed-up and efficient extraction in a single architecture, especially for extremely large extraction decay rates. However, this goal remains elusive so far. Current approaches to enhance photon extraction decay rates for plasmonic nanostructures, including hybrid antennas, plasmonic cavities, photonic hypercrystals, and metamaterials, are either dependent on hybrid plasmonic modes, which suffer from structural complexity, or limited by poor outcoupling efficiency. Here, we propose a novel paradigm-spatial topological transition in the architecture of feasible metamaterial structure (e.g., an array of silver flat-topped conical rods), which can strongly enhance the photon extraction decay rate of quantum emitters. The underlying physics relies on the emerging unique feature of spatial topological transitions due to the transition from elliptical to hyperbolic iso-frequency contours in a single spatially varying metamaterial. Hence, the supported high-k eigenmodes in the metamaterial can now become momentum-matched with the radiative modes. More importantly, due to the existence of elliptical and hyperbolic zones, it is possible to allow for the realization of an extremely large value of extraction decay rate. Our results thus represent a crucial step for the integration of single-photon sources into photonic quantum networks and quantum information applications.