  The search for topological excitations such as Majorana fermions has spurred
interest in the boundaries between distinct quantum states. Here, we explore an
interface between two prototypical phases of electrons with conceptually
different ground states: the integer quantum Hall insulator and the s-wave
superconductor. We find clear signatures of hybridized electron and hole states
similar to chiral Majorana fermions, to which we refer as chiral Andreev edge
states (CAES). They propagate along the interface in the direction determined
by magnetic field and their interference can turn an incoming electron into an
outgoing electron or a hole, depending on the phase accumulated by the CAES
along their path. Our results demonstrate that these excitations can propagate
and interfere over a significant length, opening future possibilities for their
coherent manipulation.
