Hetero-integrated diamond-on-AlGaN/AlN waveguides for optical color center interfacing

Quantum photonic devices require efficient access to solid-state spin qubits serving as quantum memories or single-photon sources and nonlinearities. Additionally, they demand nonlinear and electro-optic components for frequency converters and phase shifters. The serial production of quantum devices needs the on-chip integration of all these photonic components. These requirements motivate the hetero-integration of materials with complementary properties. Diamond color centers provide access to spin registers, long coherence times, and suitability for quantum networking. In contrast, aluminum gallium nitride-on-aluminum nitride (AlGaN/AlN) photonics features second-order nonlinear and first-order electro-optic effects. Here, we demonstrate the accurate integration of diamond waveguides containing nitrogen-vacancy (NV) centers into AlGaN/AlN waveguides using a pick-and-place method. Both waveguides possess tapered sections for adiabatic mode transfer. We model the tapered diamond-AlGaN/AlN interface with finite element simulations, implementing fabrication constraints and placement uncertainties. Measured coupling efficiencies coincide closely with simulation model predictions.