  Group-IV color centers in diamond are a promising light-matter interface for
quantum networking devices. The negatively charged tin-vacancy center (SnV) is
particularly interesting, as its large spin-orbit coupling offers strong
protection against phonon dephasing and robust cyclicity of its optical
transitions towards spin-photon entanglement schemes. Here, we demonstrate
multi-axis coherent control of the SnV spin qubit via an all-optical stimulated
Raman drive between the ground and excited states. We use coherent population
trapping and optically driven electronic spin resonance to confirm coherent
access to the qubit at 1.7 K, and obtain spin Rabi oscillations at a rate of
$\Omega/2\pi$=3.6(1) MHz. All-optical Ramsey interferometry reveals a spin
dephasing time of $T_2^*$=1.3(3)$\mu$s and two-pulse dynamical decoupling
already extends the spin coherence time to $T_2$=0.33(14) ms. Combined with
transform-limited photons and integration into photonic nanostructures, our
results make the SnV a competitive spin-photon building block for quantum
networks.
