  An outstanding hurdle for defect spin qubits in silicon carbide (SiC) is
single-shot readout - a deterministic measurement of the quantum state. Here,
we demonstrate single-shot readout of single defects in SiC via spin-to-charge
conversion, whereby the defect's spin state is mapped onto a long-lived charge
state. With this technique, we achieve over 80% readout fidelity without pre-
or post-selection, resulting in a high signal-to-noise ratio (SNR) that enables
us to measure long spin coherence times. Combined with pulsed dynamical
decoupling sequences in an isotopically purified host material, we report
single spin T2 > 5s, over two orders of magnitude greater than previously
reported in this system. The mapping of these coherent spin states onto single
charges unlocks both single-shot readout for scalable quantum nodes and
opportunities for electrical readout via integration with semiconductor
devices.
