  Single-photon sources are of paramount importance in quantum communication,
quantum computation, and quantum metrology. In particular, there is great
interest in realizing scalable solid-state platforms that can emit triggered
photons on demand to achieve scalable nanophotonic networks. We report on a
visible-spectrum single-photon emitter in 4H silicon carbide (SiC). The emitter
is photostable at room and low temperatures, enabling photon counts per second
in excess of 2$\times$10$^6$ from unpatterned bulk SiC. It exists in two
orthogonally polarized states, which have parallel absorption and emission
dipole orientations. Low-temperature measurements reveal a narrow zero phonon
line (linewidth $<0.1~$nm) that accounts for $>30$% of the total
photoluminescence spectrum.
