  Deterministic coupling between photonic nodes in a quantum network is an
essential step towards implementing various quantum technologies. The
omnidirectionality of free-standing emitters, however, makes this coupling
highly inefficient, in particular if the distant nodes are coupled via low
numerical aperture (NA) channels such as optical fibers. This limitation
requires placing quantum emitters in nanoantennas that can direct the photons
into the channels with very high efficiency. Moreover, to be able to scale such
technologies to a large number of channels, the placing of the emitters should
be deterministic. In this work we present a method for directly locating single
free-standing quantum emitters with high spatial accuracy at the center of
highly directional bullseye metal-dielectric nanoantennas. We further employ
non-blinking, high quantum yield colloidal quantum dots (QDs) for on-demand
single-photon emission that is uncompromised by instabilities or non-radiative
exciton recombination processes. Taken together this approach results in a
record-high collection efficiency of 85% of the single photons into a low NA of
0.5, setting the stage for efficient coupling between on-chip, room temperature
nanoantenna-emitter devices and a fiber or a remote free-space node without the
need for additional optics.
