An invariance property of the repton model

It is required on physical grounds that the eigenvalues of the transition-rate matrix of the Rubinstein-Duke repton model for all values of the spatial wave number q be invariant to the choice of marker repton. This is not immediately obvious from the structure of the transition-rate matrix itself, but we show that these matrices for different choices of marker are related by similarity transformation and therefore have the same eigenvalues.