  The quantum Hall (QH) effect supports a set of chiral edge states at the
boundary of a 2-dimensional electron gas (2DEG) system. A superconductor (SC)
contacting these states induces correlation of the quasi-particles in the
dissipationless 1D chiral QH edge states. If the superconducting electrode is
narrower than the superconducting coherence length, the incoming electron are
correlated to outgoing hole along the chiral edge state by the Andreev process.
In order to realize this crossed Andreev conversion (CAC), it is necessary to
fabricate highly transparent and nanometer-scale superconducting junctions to
QH system. Here we report the observation of CAC in a graphene QH system
contacted with a nanostructured NbN superconducting electrode. The chemical
potential of the edge states across the superconducting electrode exhibits a
sign reversal, providing direct evidence of CAC. This hybrid SC/QH system is a
novel route to create isolated non-Abelian anyonic zero modes, in resonance
with the chiral QH edge.
