All Optical Initialisation and Readout and Coherent Population Trapping of a Single Germanium Vacancy in Diamond

Optically active defects in diamond have received considerable interest as platforms for quantum information processing. Yet defects that offer the necessary photonic and spin properties have remained elusive. Here, we investigate the recently discovered, negatively charged germanium vacancy which has attractive spectral properties: its highly stable optical transitions, high Debye-Waller factor and short excited state lifetime. We demonstrate the capability to address the spin sub-levels of the germanium vacancy and thus, perform all optical spin initialisation and readout. Additionally, we generate dark coherent superpositions of the germanium vacancy spin states through coherent population trapping and use Raman spectroscopy to probe the hyperfine structure between the high spin (I=9/2) host ⁷³Ge nuclear spin and the GeV electron spin.

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