Fluctuation-dissipation theorem for chiral systems in nonequilibrium steady states

We consider a three-terminal system with a chiral edge channel connecting the source and drain terminals. Charge can tunnel between the chiral edge and a third thermal. The third terminal is maintained at a different temperature and voltage than the source and drain. We prove a general relation for the current noises detected in the drain and third terminal. It has the same structure as an equilibrium fluctuation-dissipation relation with the nonlinear response $\partial I/\partial V$ in place of the linear conductance. The result applies to a general chiral system and may be useful for detecting ``upstream'' modes on the quantum Hall edges.