  The interrelationship between localization, quantum transport, and disorder
has remained a fascinating focus in scientific research. Traditionally, it has
been widely accepted in the physics community that in one-dimensional systems,
as disorder increases, localization intensifies, triggering a metal-insulator
transition. However, a recent theoretical investigation [Phys. Rev. Lett. 126,
106803] has revealed that the interplay between dimerization and disorder leads
to a reentrant localization transition, constituting a remarkable theoretical
advancement in the field. Here, we present the experimental observation of
reentrant localization using an experimentally friendly model, a photonic SSH
lattice with random-dimer disorder, achieved by incrementally adjusting
synthetic potentials. In the presence of correlated on-site potentials, certain
eigenstates exhibit extended behavior following the localization transition as
the disorder continues to increase. We directly probe the wave function in
disordered lattices by exciting specific lattice sites and recording the light
distribution. This reentrant phenomenon is further verified by observing an
anomalous peak in the normalized participation ratio. Our study enriches the
understanding of transport in disordered mediums and accentuates the
substantial potential of integrated photonics for the simulation of intricate
condensed matter physics phenomena.
