  Plasmonic nanoantennas have the ability to confine and enhance incident
electromagnetic fields into very sub-wavelength volumes, while at the same time
efficiently radiating energy to the far-field. These properties have allowed
plasmonic nanoantennas to be extensively used for exciting quantum
emitters-such as molecules and quantum dots-and also for the extraction of
photons from them for measurements in the far-field. Due to electromagnetic
reciprocity, it is expected that plasmonic nanoantennas radiate energy as
efficiently as an external source can couple energy to them. In this paper, we
adopt a multipole expansion (Mie theory) and numerical simulations to show that
although reciprocity holds, certain plasmonic antennas radiate energy much more
efficiently than one can couple energy into them. This work paves the way
towards designing plasmonic antennas with specific properties for applications
where the near-to-far-field relationship is of high significance, such as:
surface-enhanced Raman spectroscopy, strong coupling at room temperature, and
the engineering of quantum states in nanoplasmonic devices.
