Effective integration of highly-efficient focusing apodized grating and quantum dots on a solid substrate for scalable quantum photonic circuits

Recent advancements in quantum photonic circuits have significantly influenced the field of quantum information processing. The pursuit of an integrated quantum photonic circuit that offers an active, stable platform for large-scale integration and high processing efficiency remains a key objective. The grating coupler, as a crucial element for an efficient transformation output interface in the integrated quantum photonic circuits, presents significant potential for practical applications. Here, we demonstrate the integration block of a highly efficient shallow-etched focusing apodized grating coupler with indium arsenide (InAs) quantum dots (QDs) in gallium arsenide (GaAs) on a SiO₂ substrate for active quantum photonic circuits. The designed grating couplers possess a high efficiency over 90% in the broadband (900–930 nm) from the circuit to free space, and a nearly-perfect match with the fiber mode. Experimentally, the efficiency to free space reaches 81.8%, and the match degree with the fiber mode is high up to 92.1%. The proposed integration block offers the potential for large-scale integration of active quantum photonic circuits due to its stable solid substrate and highly performant output for quantum measurements.