Group IV Vacancy Defects in Diamond: Sense and Sensitivity
Prof. Dr. Christoph Becher (Universität des Saarlandes)

Quantum bits based on solid-state spins are promising and potentially scalable systems for the implementation of quantum technologies ranging from quantum information processing to quantum-enhanced sensing and metrology. Ideally, they combine individually addressable spins with very long coherence times, optical emission spectra with narrow homogeneous and inhomogeneous broadenings and bright single-photon emission. In this respect, impurity-vacancy color centers in diamond based on group-IV elements (SiV, GeV, SnV, PbV) have emerged as interesting systems promising to combine all desired favorable properties.
Here, we report on recent experiments on SnV centers where we find promising optical and spin properties: The negatively charged SnV(-) center is a bright single photon emitter, showing a narrow inhomogeneous distribution of zero phonon lines in a high-temperature annealed sample and truly lifetime-limited transition linewidths down to 20 MHz. We explore the charge transition cycle upon resonant excitation which leads to shelving in the dark SnV(2-) state and find that illumination with a second light field in the blue spectral range leads to fast and efficient initialization into the desired negative charge state. The charge-stabilized SnV(-) center exhibits exceptional spectral stability with very small spectral diffusion (4 MHz on a homogenous linewidth of 25 MHz over 1 hour) and promising spin dephasing time (5 µs, measured via coherent population trapping).
We discuss possible applications in quantum communication, based on the prospects of coherent spin manipulation and generation of indistinguishable single photons, as well as in quantum sensing by exploiting the option of all-optical sensing schemes.

J. Görlitz et al., Coherence of a charge stabilised tin-vacancy spin in diamond, npj Quantum Inf. 8, 45 (2022).