  Unlike radiowave antennas, optical nanoantennas so far cannot be fed by
electrical generators. Instead, they are driven by light or via optically
active materials in their proximity. Here, we demonstrate direct electrical
driving of an optical nanoantenna featuring an atomic-scale feed gap. Upon
applying a voltage, quantum tunneling of electrons across the feed gap creates
broadband quantum shot noise. Its optical frequency components are efficiently
converted into photons by the antenna. We demonstrate that the properties of
the emitted photons are fully controlled by the antenna architecture, and that
the antenna improves the quantum efficiency by up to two orders of magnitude
with respect to a non-resonant reference system. Our work represents a new
paradigm for interfacing electrons and photons at the nanometer scale, e.g. for
on-chip wireless data communication, electrically driven single- and
multiphoton sources, as well as for background-free linear and nonlinear
spectroscopy and sensing with nanometer resolution.
