  We introduce the quantum mechanical formalism for treating surface plasmon
polariton scattering at an interface. Our developed theory - which is
fundamentally different from the analogous photonic scenario - is used to
investigate the possibility of plasmonic beamsplitters at the quantum level.
Remarkably, we find that a wide-range of splitting ratios can be reached. As an
application, we characterize a 50:50 plasmonic beamsplitter and investigate
first-order quantum interference of surface plasmon polaritons. The results of
this theoretical study show that surface plasmon beamsplitters are able to
reliably and efficiently operate in the quantum domain.

Quantum Physics;Mesoscale and Nanoscale Physics;Optics