  Recent progress in nanotechnology has enabled us to fabricate subwavelength
architectures that function as antennas for improving the exchange of optical
energy with nanoscale matter. We describe the main features of optical antennas
for enhancing quantum emitters and review designs that increase the spontaneous
emission rate by orders of magnitude from the ultraviolet up to the
near-infrared spectral range. To further explore how optical antennas may lead
to unprecedented regimes of light-matter interaction, we draw a relationship
between metal nanoparticles, radio-wave antennas and optical resonators. Our
analysis points out how optical antennas may function as nanoscale resonators
and how these may offer unique opportunities with respect to state-of-the-art
microcavities.

Optics;Quantum Physics