  Nanophotonic interfaces between single emitters and light promise to enable
new quantum optical technologies. Here, we use a combination of finite element
simulations and analytic quantum theory to investigate the interaction of
various quantum emitters with slot-waveguide rings. We predict that for rings
with radii as small as 1.44 $\mu$m (Q = 27,900), near-unity emitter-waveguide
coupling efficiencies and emission enhancements on the order of 1300 can be
achieved. By tuning the ring geometry or introducing losses, we show that
realistic emitter-ring systems can be made to be either weakly or strongly
coupled, so that we can observe Rabi oscillations in the decay dynamics even
for micron-sized rings. Moreover, we demonstrate that slot waveguide rings can
be used to directionally couple emission, again with near-unity efficiency. Our
results pave the way for integrated solid-state quantum circuits involving
various emitters.
