Spontaneous radiation of a two-level atom into multipole modes of a plasmonic nanoparticle

•We consider the relaxation of an excited two-level system (TLS) positioned near a spherical plasmonic nanoparticle (NP).•The transition frequency of the TLS coincides with the frequency of the condensation point of the NP plasmonic resonances.•The relaxation of the TLS excitation is a two-step process. At the first step, the relaxation is exponential.•At the second step, the exponential decay breaks into Rabi oscillations.•The probability of the TLS being in the excited state exhibits either chaotic or nearly regular oscillations.

We consider the relaxation of an excited two-level system (TLS) positioned near a spherical plasmonic nanoparticle (NP). The transition frequency of the TLS is assumed to coincide with the frequency of the condensation point of NP plasmonic resonances. We show that the relaxation of the TLS excitation is a two-step process. Following an initial exponential decay, the TLS breaks in to Rabi oscillations. Depending upon the distance between the TLS and NP, the probability of the TLS being in the excited state exhibits either chaotic or nearly regular oscillations. In the latter case, the eigenfrequency of the TLS-NP system coincides with one of NP multipole modes.