  We provide a general theoretical platform based on quantized radiation in
absorptive and inhomogeneous media for investigating the coherent interaction
of light with metallic structures in the immediate vicinity of quantum
emitters. In the case of a very small metallic cluster, we demonstrate extreme
regimes where a single emitter can either counteract or enhance particle
absorption by three orders of magnitude. For larger structures, we show that an
emitter can eliminate both scattering and absorption and cloak a plasmonic
antenna. We provide physical interpretations of our results and discuss their
applications in active metamaterials and quantum plasmonics.
