  Optical nanoantennas, i.e., elements transforming localized light or
waveguide modes into freely propagating fields and vice versa, are vital
components for modern nanophotonics. Optical antennas have been demonstrated to
cause the Dicke superradiance effect, i.e., collective spontaneous emission of
quantum sources. However, the impact of coherent excitation on the antenna
performance, such as directivity, efficiency, and Purcell effect, remains
mostly unexplored. Herein, using full-wave numerical simulations backed by a
quantum model, we unveil that coherent excitation allows controlling antenna
multipoles, on-demand excitation of nonradiative states, enhanced directivity
and improves antenna radiation efficiency. This collective excitation
corresponds to the states with nonzero dipole moment in the quantum picture,
where the quantum phase is well defined. The results of this work bring another
degree of freedom - the collective phase of an ensemble of quantum emitters -
to control optical nanoantennas and, as such, pave the way to the use of
collective excitations for nanophotonic devices with superb performance. To
make the discussion independent of the frequency range, we consider the
all-dielectric design and use dimensionless units.
