Photonic integrated circuits (PICs) are attractive platforms to perform large-scale quantum information processing. While highly functional PICs (e.g., silicon-based photonic circuits) and high-performance single-photon sources [SPSs, e.g., compound-semiconductor quantum dots (QDs)] have been independently demonstrated, their combination for single-photon-based applications has still been limited. This is largely due to the complexities of introducing SPSs into existing PIC platforms, which are generally realized with different materials and using distinct fabrication protocols. Here, we report a novel approach to combine SPSs and PICs prepared independently. We employ transfer printing, by which multiple desired SPSs can be integrated in a simple pick-and-place manner with a theoretical waveguide coupling efficiency >99%, fulfilling the demanding requirements of large-scale quantum applications. Experimentally, we demonstrated QD-based SPSs with high waveguide coupling efficiencies, together with the integration of two SPSs into a waveguide. Our approach will accelerate scalable fusion between modern PICs and cutting-edge quantum technologies.
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