  Entanglement between two qubits (two level atoms) mediated by surface
plasmons in three-dimensional plasmonic waveguides is studied using a quantum
master equation formalism. Two types of waveguides, a nanowire and a V-shaped
channel cut in a flat metal plane, are considered. The Green functions for the
waveguides, which rigorously describes the dissipative qubit environment, are
calculated numerically using a direct finite-difference time-domain (FDTD)
solution of Maxwell's equations. Finite-length effects are shown to play a
crucial role in enhancing entanglement, and resonant-length plasmonic
waveguides can provide higher entanglement between qubits than infinite-length
waveguides. It is also shown that coupling slots can improve entanglement via
stronger qubit-waveguide coupling, for both the infinite- and finite-waveguide
cases.
