  Vanadium in silicon carbide (SiC) is emerging as an important candidate
system for quantum technology due to its optical transitions in the telecom
wavelength range. However, several key characteristics of this defect family
including their spin relaxation lifetime (T1), charge state dynamics, and level
structure are not fully understood. In this work, we determine the T1 of an
ensemble of vanadium defects, demonstrating that it can be greatly enhanced at
low temperature. We observe a large spin contrast exceeding 90% and long
spin-relaxation times of up to 25s at 100mK, and of order 1s at 1.3K. These
measurements are complemented by a characterization of the ensemble charge
state dynamics. The stable electron spin furthermore enables high-resolution
characterization of the systems' hyperfine level structure via two-photon
magneto-spectroscopy. The acquired insights point towards high-performance
spin-photon interfaces based on vanadium in SiC.
