Quantum dot plasmonics: from weak to strong coupling

The complementary optical properties of surface plasmon excitations of metal nanostructures and long-lived excitations of semiconductor quantum dots (QDs) make them excellent candidates for studies of optical coupling at the nanoscale level. Plasmonic devices confine light to nanometer-sized regions of space, which turns them into effective cavities for quantum emitters. QDs possess large oscillator strengths and high photostability, making them useful for studies down to the single-particle level. Depending on structure and energy scales, QD excitons and surface plasmons (SPs) can couple either weakly or strongly, resulting in different unique optical properties. While in the weak coupling regime plasmonic cavities (PCs) mostly enhance the radiative rate of an emitter, in the strong coupling regime the energy level of the two systems mix together, forming coupled matter-light states. The interaction of QD excitons with PCs has been widely investigated experimentally as well as theoretically, with an eye on potential applications ranging from sensing to quantum information technology. In this review we provide a comprehensive introduction to this exciting field of current research, and an overview of studies of QD-plasmon systems in the weak and strong coupling regimes.