We present an experimental study of a gate-defined quantum point contact made on high-mobility graphene devices. Unlike usual 2D electron gases that can be fully depleted by electrostatic gating, the semi-metal character of graphene leads to the formation of transparent p-n junctions beneath gate electrodes. In this talk I will show that, in the quantum Hall regime of graphene, one can use p-n junction interfaces to guide quantum Hall edge channels and confine them into a n-p-n constriction. I will discuss the delicate regime of equilibration between electron and hole quantum Hall edge channels at the p-n junction interfaces, and show that there is a significant, equilibration-free gate parameters range that enables to operate the quantum point contact. Application to tunneling experiments in the fractional quantum Hall regime will be also discussed.