Competition between finite-size effects and dipole-dipole interactions in few-atom systems

In this paper, we study the competition between finite-size effects (i.e. discernibility of particles) and dipole-dipole interactions in few-atom systems coupled to the electromagnetic field in vacuum. We consider two hallmarks of cooperative effects, superradiance and subradiance, and compute for each the rate of energy radiated by the atoms and the coherence of the atomic state during the time evolution. We adopt a statistical approach in order to extract the typical behavior of the atomic dynamics and average over random atomic distributions in spherical containers with prescribed $k_0R$ with $k_0$ the radiation wavenumber and $R$ the average interatomic distance. Our approach allows us to highlight the tradeoff between finite-size effects and dipole-dipole interactions in superradiance/subradiance. In particular, we show the existence of an optimal value of $k_0R$ for which the superradiant intensity and coherence pulses are the less affected by dephasing effects induced by dipole-dipole interactions and finite-size effects.