  We investigate transport in a gate-defined graphene quantum point contact in
the quantum Hall regime. Edge states confined to the interface of p and n
regions in the graphene sheet are controllably brought together from opposite
sides of the sample and allowed to mix in this split-gate geometry. Among the
expected quantum Hall features, an unexpected additional plateau at 0.5 h/e^2
is observed. We propose that chaotic mixing of edge channels gives rise to the
extra plateau.
