  Semiconductor quantum dots (QDs) provide an essential link between light and
matter in emerging fields such as light-harvesting, all-solid-state quantum
communication, and quantum computing. QDs are excellent single-photon sources
and can store quantum bits for extended periods making them promising
interconnects between light and matter in integrated quantum information
networks. To this end the light-matter interaction strength must be strongly
enhanced using nanophotonic structures such as photonic crystal cavities and
waveguides or plasmonic nanowires. So far it has been assumed that QDs can be
treated just like atomic photon emitters where the spatial properties of the
wavefunction can be safely ignored. Here we demonstrate that the point-emitter
description for QDs near plasmonic nanostructures breaks down. We observe that
the QDs can excite plasmons eight times more efficiently depending on their
orientation due to their mesoscopic character. Either enhancement or suppresion
of the rate of plasmon excitation is observed depending on the geometry of the
plasmonic nanostructure in full agreement with a new theory. This discovery has
no equivalence in atomic systems and paves the way for novel nanophotonic
devices that exploit the extended size of QDs as a resource for increasing the
light-matter interaction strength.
