Transmission of phase information between electrons and holes in graphene

We have studied quantum interference between electrons and holes in a split-ring gold interferometer with graphene arms, one of which contained a pn junction. The carrier type, the pn junction and the phase of the oscillations in a magnetic field were controlled by a top gate placed over one of the arms. We observe clear Aharonov-Bohm oscillations at the Dirac point and away from it, regardless of the carrier type in each arm. We also find clear oscillations when one arm of the interferometer contains a single pn junction, allowing us to study the interplay of Aharonov-Bohm effect and Klein tunneling.