Interaction and Entanglement of a Pair of Quantum Emitters near a Nanoparticle: Analysis beyond ElectricDipole Approximation In this paper, we study the collective effects which appear as a pair of quantum emitters is positioned in close vicinity to a plasmonic nanoparticle. These effects include multipolexe2x80x93multipole interaction and collective decay, the strengths and rates of which are modified by the presence of the nanoparticle. As a result, entanglement is generated between the quantum emitters, which survives in the stationary state. To evaluate these effects, we exploit the Greenxe2x80x99s tensorbased quantization scheme in the Markovian limit, taking into account the corrections from lightxe2x80x93matter coupling channels higher than the electric dipole. We find these higherorder channels to significantly influence the collective rates and degree of entanglement, and in particular, to qualitatively influence their spatial profiles. Our findings indicate that, apart from quantitatively modifying the results, the higherorder interaction channels may introduce asymmetry into the spatial distribution of the collective response.

Multipartite Entanglement Generation in a Structured Environment In this paper, we investigate the entanglement generation of nqubit states in a model consisting of n independent qubits, each coupled to a harmonic oscillator which is in turn coupled to a bath of N additional harmonic oscillators with nearestneighbor coupling. With analysis, we can find that the steady multipartite entanglement with different values can be generated after a longtime evolution for different sizes of the quantum system. Under weak coupling between the system and the harmonic oscillator, multipartite entanglement can monotonically increase from zero to a stable value. Under strong coupling, multipartite entanglement generation shows a speedup increase accompanied by some oscillations as nonMarkovian behavior. Our results imply that the strong coupling between the harmonic oscillator and the N additional harmonic oscillators, and the large size of the additional oscillators will enhance nonMarkovian dynamics and make it take a very long time for the entanglement to reach a stable value. Meanwhile, the couplings between the additional harmonic oscillators and the decay rate of additional harmonic oscillators have almost no effect on the multipartite entanglement generation. Finally, the entanglement generation of the additional harmonic oscillators is also discussed.