  Photonic lattices enable experimental exploration of transport and
localization phenomena, two of the mayor goals in physics and technology. In
particular, the optical excitation of some lattice sites which evanescently
couple to a lattice array emulates radiation processes into structured
reservoirs, a fundamental subject in quantum optics. Moreover, the simultaneous
excitation of two sites simulates collective phenomena, leading to
phase-controlled enhanced or suppressed radiation, namely super and
subradiance. This work presents an experimental study of collective radiative
processes on a photonic kagome lattice. A single or simultaneous -- in or
out-of-phase -- excitation of the outlying sites controls the radiation
dynamics. Specifically, we demonstrate a controlable transition between a fully
localized profile at the two outlying sites and a completely dispersed state
into the quasi-continuum. Our result presents photonic lattices as a platform
to emulate and experimentally explore quantum optical phenomena in
two-dimensional structured reservoirs, while harnessing such phenomena for
controlling transport dynamics and implementing all-optical switching devices.
