Strong coupling between localized surface plasmons and point-like emitters within the classical scheme of the discrete dipole approximation

In this work, the possibility to achieve strong coupling between localized surface plasmons and point-like emitters and to theoretically predict this phenomenon within the classical framework of the Discrete Dipole Approximation (DDA), is reported. DDA allows to calculate the perturbations induced by any kind of metal nanostructure onto the decay dynamics of an oscillating dipole with a good level of accuracy and, if combined with a quantum electrodynamical treatment of radiation-matter interaction, can result in a powerful scheme which can be applied to nanoparticles of any shape and dispersive dielectric function. Here this approach is applied to sharp silver nanotips, demonstrating the advantage offered by these nanostructures with respect to spherically-shaped ones in reducing the threshold for the onset of strong coupling in the electromagnetic interaction of a point-like emitter with localized surface plasmons.