  We observe Wannier-Stark localization in curved photonic lattices, realized
using arrays of evanescently coupled optical waveguides. By correctly tuning
the strength of inter-site coupling in the lattice, we observe that
Wannier-Stark states become increasingly localized, and eventually fully
localized to one site, as the curvature of the lattice is increased. We then
demonstrate that tunneling can be successfully restored in the lattice by
applying a sinusoidal modulation to the lattice position, an effect that is a
direct analogue of photon-assisted tunneling. This precise tuning of the
tunneling matrix elements, through laser-fabricated on-site modulations, opens
a novel route for the creation of gauge fields in photonic lattices.
