  Coupling superconductors to quantum Hall edge states is the subject of
intense investigation as part of the ongoing search for non-abelian
excitations. Our group has previously observed supercurrents of hundreds of
picoamperes in graphene Josephson junctions in the quantum Hall regime. One of
the explanations of this phenomenon involves the coupling of an electron edge
state on one side of the junction to a hole edge state on the opposite side. In
our previous samples, these states are separated by several microns. Here, a
narrow trench perpendicular to the contacts creates counterpropagating quantum
Hall edge channels tens of nanometres from each other. Transport measurements
demonstrate a change in the low-field Fraunhofer interference pattern for
trench devices and show a supercurrent in both trench and reference junctions
in the quantum Hall regime. The trench junctions show no enhancement of quantum
Hall supercurrent and an unexpected supercurrent periodicity with applied
field, suggesting the need for further optimization of device parameters.
