  Diamond colour centres are promising optically-addressable solid state spins
that can be matter-qubits, mediate deterministic interaction between photons
and act as single photon emitters. Useful quantum computers will comprise
millions of logical qubits. To become useful in constructing quantum computers,
spin-photon interfaces must therefore become scalable and be compatible with
mass-manufacturable photonics and electronics. Here we demonstrate
heterogeneous integration of NV centres in nanodiamond with low-fluorescence
silicon nitride photonics from a standard 180 nm CMOS foundry process.
Nanodiamonds are positioned over pre-defined sites in a regular array on a
waveguide, in a single post-processing step. Using an array of optical fibres,
we excite NV centres selectively from an array of six integrated nanodiamond
sites, and collect the photoluminescence (PL) in each case into waveguide
circuitry on-chip. We verify single photon emission by an on-chip Hanbury Brown
and Twiss cross-correlation measurement, which is a key characterisation
experiment otherwise typically performed routinely with discrete optics. Our
work opens up a simple and effective route to simultaneously address large
arrays of individual optically-active spins at scale, without requiring
discrete bulk optical setups. This is enabled by the heterogeneous integration
of NV centre nanodiamonds with CMOS photonics.
