  Ordered media often support vortex structures with intriguing topological
properties. Here, we investigate non-Abelian vortices in tetrahedral order,
which appear in the cyclic phase of spin-2 Bose--Einstein condensates and in
the tetrahedratic phase of bent-core nematic liquid crystals. Using these
vortices, we construct topologically protected knots in the sense that they
cannot decay into unlinked simple loop defects through vortex crossings and
reconnections without destroying the phase. The discovered structures are the
first examples of knots bearing such topological protection in a known
experimentally realizable system.
