1 Quantum Photonics, Department of Photonics Engineering, Technical University of Denmark2 Department of Photonics Engineering, Technical University of Denmark3 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
This thesis reports research on quantum dots coupled to dielectric and plasmonic nano-structures by way of nano-structure fabrication, optical measurements, and theoretical modeling. To study light-matter interaction, plasmonic gap waveguides with nanometer dimensions as well as samples for studies of quantum dots in proximity to semiconductor/air and semiconductor/metal interfaces, were fabricated. We measured the decay dynamics of quantum dots near plasmonic gap waveguides and observed modied decay rates. The obtainable modications with the fabricated structures are calculated to be too small to allow for e- cient plasmon-based single-photon sources. Theoretical studies of coupling and propagation properties of plasmonic waveguides reveal that a high-refractive index of the medium surrounding the emitter, e.g. nGaAs = 3.5, limits the realizability of ecient plasmon-based single-photon sources using self-assembled quantum dots. The measured decay dynamics of quantum dots in proximity to semiconductor/ metal interfaces reveal that the dipole approximation generally does not hold for quantum dots due to their mesoscopic size. In order to explain the observations, a theoretical model for the spontaneous emission of mesoscopic quantum emitters is developed. The light-matter interaction is in this model modied beyond the dipole expectancy and found to both suppress and enhance the coupling to plasmonic modes in excellent agreement with our measurements. We demonstrate that this mesoscopic effect can be utilized to strongly modify the coupling to plasmonic modes on metal nanowires and gap waveguides and we propose its use for spontaneous-emission control beyond the dipole approximation in nano-structured environments in general. The mesoscopic effect can be utilized to strongly modify the coupling to plasmonic modes on metal nanowires and gap waveguides. We fabricate plasmonic gap waveguides and study the coupling of single quantum dots to these.