  We realize a photonic analog simulator of the quantum Rabi model, based on
light transport in femtosecond-laser-written waveguide superlattices, which
provides an experimentally accessible testbed to explore the physics of
light-matter interaction in the deep strong coupling regime. Our optical
setting enables to visualize dynamical regimes not yet accessible in cavity or
circuit quantum electrodynamics, such as bouncing of photon number wave packets
in parity chains of Hilbert space.
