  Modifying light fields at single-photon level is a key challenge for upcoming
quantum technologies and can be realized in a scalable manner through
integrated quantum photonics. Laser-written diamond photonics offers
three-dimensional fabrication capabilities and large mode-field diameters
matched to fiber optic technology, though limiting the cooperativity at the
single-emitter level. To realize large cooperativities, we combine excitation
of single shallow-implanted silicon vacancy centers via large numerical
aperture optics with detection assisted by laser-written type-II waveguides. We
demonstrate single-emitter extinction measurements with a cooperativity of
0.153 and a beta factor of 13% yielding 15.3% as lower bound for the quantum
efficiency of a single emitter. The transmission of resonant photons reveals
single-photon subtraction from a quasi-coherent field resulting in
super-Poissonian light statistics. Our architecture enables single quantum
level light field engineering in an integrated design which can be fabricated
in three dimensions and with a natural connectivity to optical fiber arrays.
