  We develop a consistent quantum description of surface plasmons interacting
with quantum emitters and external electromagnetic field. Within the framework
of macroscopic electrodynamics in dispersive and absorptive medium, we derive,
in the Markov approximation, the canonical Hamiltonian, commutation relations,
and coupling parameters for the plasmon modes in metal-dielectric structures of
an arbitrary shape whose characteristic size is well below the diffraction
limit. We then develop a new quantum approach bridging the macroscopic and
canonical schemes which describes the interacting plasmons in terms of bosonic
modes with linear dispersion whose coupling to the electromagnetic field and
quantum emitters is mediated by the classical plasmons. By accurately
accounting for medium optical dispersion and losses in the interactions of
surface plasmons with light and localized electron excitations, this approach
can serve as a framework for studying non-Markovian effects in plasmonics.
