  We analyze the disorder-perturbed transport of quantum states in the absence
of backscattering. This comprises, for instance, the propagation of edge-mode
wave packets in topological insulators, or the propagation of photons in
inhomogeneous media. We quantify the disorder-induced dephasing, which we show
to be bound. Moreover, we identify a gap condition to remain in the
backscattering-free regime despite disorder-induced momentum broadening. Our
analysis comprises the full disorder-averaged quantum state, on the level of
both populations and coherences, appreciating states as potential carriers of
quantum information. The well-definedness of states is guaranteed by our
treatment of the nonequilibrium dynamics with Lindblad master equations.
