  Photonic integration is an enabling technology for photonic quantum science,
offering greater scalability, stability, and functionality than traditional
bulk optics. Here, we describe a scalable, heterogeneous III-V/silicon
integration platform to produce Si$_3$N$_4$ photonic circuits incorporating
GaAs-based nanophotonic devices containing self-assembled InAs/GaAs quantum
dots. We demonstrate pure singlephoton emission from individual quantum dots in
GaAs waveguides and cavities - where strong control of spontaneous emission
rate is observed - directly launched into Si$_3$N$_4$ waveguides with > 90 %
efficiency through evanescent coupling. To date, InAs/GaAs quantum dots
constitute the most promising solidstate triggered single-photon sources,
offering bright, pure and indistinguishable emission that can be electrically
and optically controlled. Si$_3$N$_4$ waveguides offer low-loss propagation,
tailorable dispersion and high Kerr nonlinearities, desirable for linear and
nonlinear optical signal processing down to the quantum level. We combine these
two in an integration platform that will enable a new class of scalable,
efficient and versatile integrated quantum photonic devices
