Engineered electron-phonon interaction of negatively charged Silicon-Vacancy center in nanostructured diamond.

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The aim of the project is to prolong coherence properties of SiV-center while operating at moderate temperatures of few Kelvin. We pursue two strategies. 1) Employing SiV- center in nanodiamonds (NDs) introduces a cut-off frequency for resonant phonon modes. When working with sizes of a few tens of nanometers phonon frequencies below the relevant fine structure transition will be suppressed. Challenges for this strategy arise from the small size and therefore the proximity of the SiV-center to the diamond surface resulting in photo-instability and spectral-instability. Methods include chemical stabilization of SiV-center in NDs and improvements in ND production process. 2) Since spin relaxation originates from interaction with phonon modes of E point-group symmetry the spin relaxation can be reduced by embedding SiV-centers in nano-mechanical resonators where density of available phonon states is reduced and coupling to E phonon modes that are resonant with fine structure transitions is suppressed. Main advantage compared to SiV- center in NDs is the increased structure size. The emitters are further away from the diamond surface resulting in bulk-like optical properties. Main challenges of this strategy arise from dedicated diamond nano-structuring and fabrication of nano-pillar structures (NPs) of various geometry as well as positioning of SiV-center within phononic mode. With this project, we establish a new quantum emitter with excellent optical properties and long coherence times at moderate temperatures with potential applications in Quantum repeaters, Quantum sensing, or Quantum Information.