Topological heat current in a thermal equilibrium

We investigate the role of topological light states in the transport of thermally generated radiation at a thermodynamic equilibrium. Remarkably, even when the field fluctuations are purely quantum mechanical, i.e., in the zero temperature limit, there is a persistent transport of energy in the cavity in closed orbits, stemmed in two spatially separated unidirectional topological channels. In general, the persistent heat current is associated with a nontrivial electromagnetic orbital angular momentum of light.