  We demonstrate the use of a quantum transport model to study heavily graded
graphene p-n junctions in the quantum Hall regime. A combination of p-n
interface roughness and delta function disorder potential allows us to compare
experimental results on different devices from the literature. We find that
wide p-n junctions suppress mixing of $n \neq 0$ Landau levels. Our simulations
spatially resolve carrier transport in the device, for the first time,
revealing separation of higher order Landau levels in strongly graded
junctions, which suppresses mixing.
