  Optically interfaced spins in the solid promise scalable quantum networks.
Robust and reliable optical properties have so far been restricted to systems
with inversion symmetry. Here, we release this stringent constraint by
demonstrating outstanding optical and spin properties of single silicon vacancy
centres in silicon carbide. Despite the lack of inversion symmetry, the
system's particular wave function symmetry decouples its optical properties
from magnetic and electric fields, as well as from local strain. This provides
a high-fidelity spin-to-photon interface with exceptionally stable and narrow
optical transitions, low inhomogeneous broadening, and a large fraction of
resonantly emitted photons. Further, the weak spin-phonon coupling results in
electron spin coherence times comparable with nitrogen-vacancy centres in
diamond. This allows us to demonstrate coherent hyperfine coupling to single
nuclear spins, which can be exploited as qubit memories. Our findings promise
quantum network applications using integrated semiconductor-based
spin-to-photon interfaces.
