  Decoherence largely limits the physical realization of qubits and its
mitigation is critical to quantum science. Here, we construct a robust qubit
embedded in a decoherence-protected subspace, obtained by hybridizing an
applied microwave drive with the ground-state electron spin of a silicon
carbide divacancy defect. The qubit is protected from magnetic, electric, and
temperature fluctuations, which account for nearly all relevant decoherence
channels in the solid state. This culminates in an increase of the qubit's
inhomogeneous dephasing time by over four orders of magnitude (to > 22
milliseconds), while its Hahn-echo coherence time approaches 64 milliseconds.
Requiring few key platform-independent components, this result suggests that
substantial coherence improvements can be achieved in a wide selection of
quantum architectures.
