Final Report Summary - PLACQED (Plasmonic cavity quantum electrodynamics with diamond-based quantum systems) This project aims to realize plasmonic cavity quantum electrodynamics using optically active diamond-based quantum systems such as atomic impurities and metal-dielectric contructs on nanometer dimensions. Color centers in diamond provide a suitable test bed for applications of quantum information processing, as well as selected spin-spin interactions. While there are hundreds of known color centers in diamond, only one (nitrogen vacancy) is studied extensively within the remit of quantum information processing. To this end, we have focused on chromium-based and silicon-based colour centres as viable alternatives from both photonics and spin perspectives. Indeed we managed to observe one of the narrowest typical linewidths for diamond-based emitters to-date. We further showed that the optical transition frequency can be tuned significantly via an applied voltage rendering these systems attractive for spectral control of photonic states. The next challenge was to demonstrate optical addressability of the internal degrees of freedom such as electronic spin.We then proceeded to show that resonant optical excitation leads to spin-tagged fluorescence for silicon-vacancy centres with high spin purity. In parallel, we have shown spectral tunability of a plasmonic nanoantenna mode by modifying the antenna environment in a controlled fashion via nanopositioning a dielectric nanostructure. We also achieved first individual then multiple coherently coupled emitter-antenna systems as a testbed for plasmon-based electro-optic circuitry.
