  We report the experimental realization of a cross-linked chiral ladder with
ultracold fermionic atoms in an optical lattice. In the ladder, the legs are
formed by the orbital states of the optical lattice and the complex inter-leg
links are generated by the orbital-changing Raman transitions that are driven
by a moving lattice potential superimposed onto the optical lattice. The
effective magnetic flux per ladder plaquette is tuned by the spatial
periodicity of the moving lattice, and the chiral currents are observed from
the asymmetric momentum distributions of the orbitals. The effect of the
complex cross links is demonstrated in quench dynamics by measuring the
momentum dependence of the inter-orbital coupling strength. We discuss the
topological phase transition of the chiral ladder system for the variations of
the complex cross links.
