  Chiral edge states are a hallmark of quantum Hall physics. In electronic
systems, they appear as a macroscopic consequence of the cyclotron orbits
induced by a magnetic field, which are naturally truncated at the physical
boundary of the sample. Here we report on the experimental realization of
chiral edge states in a ribbon geometry with an ultracold gas of neutral
fermions subjected to an artificial gauge field. By imaging individual sites
along a synthetic dimension, we detect the existence of the edge states,
investigate the onset of chirality as a function of the bulk-edge coupling, and
observe the edge-cyclotron orbits induced during a quench dynamics. The
realization of fermionic chiral edge states is a fundamental achievement, which
opens the door towards experiments including edge state interferometry and the
study of non-Abelian anyons in atomic systems.
