  We investigate theoretically the non-Markovian dynamics of a degenerate
V-type quantum emitter in the vicinity of a metallic nanosphere, a system that
exhibits quantum interference in spontaneous emission due to the anisotropic
Purcell effect. We calculate numerically the electromagnetic Green's tensor and
employ the effective modes differential equation method for calculating the
quantum dynamics of the emitter population, with respect to the resonance
frequency and the initial state of the emitter, as well as its distance from
the nanosphere. We find that the emitter population evolution varies between a
gradually total decay and a partial decay combined with oscillatory population
dynamics, depending strongly on the specific values of the above three
parameters. Under strong coupling conditions, coherent population trapping can
be observed in this system. We compare our exact results with results when the
flat continuum approximation for the modified by the metallic nanosphere vacuum
is applied. We conclude that the flat continuum approximation is an excellent
approximation only when the spectral density of the system under study is
characterized by non-overlapping plasmonic resonances.
