  There has been great interest in realizing quantum simulators of charged
particles in artificial gauge fields. Here, we perform the first quantum
simulation explorations of the combination of artificial gauge fields and
disorder. Using synthetic lattice techniques based on parametrically-coupled
atomic momentum states, we engineer zigzag chains with a tunable homogeneous
flux. The breaking of time-reversal symmetry by the applied flux leads to
analogs of spin-orbit coupling and spin-momentum locking, which we observe
directly through the chiral dynamics of atoms initialized to single lattice
sites. We additionally introduce precisely controlled disorder in the site
energy landscape, allowing us to explore the interplay of disorder and large
effective magnetic fields. The combination of correlated disorder and
controlled intra- and inter-row tunneling in this system naturally supports
energy-dependent localization, relating to a single-particle mobility edge. We
measure the localization properties of the extremal eigenstates of this system,
the ground state and the most-excited state, and demonstrate clear evidence for
a flux-dependent mobility edge. These measurements constitute the first direct
evidence for energy-dependent localization in a lower-dimensional system, as
well as the first explorations of the combined influence of artificial gauge
fields and engineered disorder. Moreover, we provide direct evidence for
interaction shifts of the localization transitions for both low- and
high-energy eigenstates in correlated disorder, relating to the presence of a
many-body mobility edge. The unique combination of strong interactions,
controlled disorder, and tunable artificial gauge fields present in this
synthetic lattice system should enable myriad explorations into intriguing
correlated transport phenomena.
