  We present the fabrication and characterization of an optical antenna that
converts the dipolar radiation of a quantum emitter to a directional beam with
99% efficiency. Aside from its implications for efficient detection of
nanoscopic emitters, this antenna facilitates a deterministic single-photon
source with applications in quantum information processing, metrology and
sub-shot-noise detection of absorption. We discuss the photophysical
limitations of the currently used quantum emitters for the realization of such
a device.
