  We explore the collective Zeno dynamics of giant artificial atoms that are
coupled, via multiple coupling points, to a common photonic or acoustic
reservoir. In this regime, the establishment of atomic cooperativity and the
revivification of exponential decay, are highly intertwined, which is utterly
beyond the non-Markovian regime with only retarded backaction. We reveal that
giant atoms build up their collective emission smoothly from the decay rate of
zero to that predicted by Markovian approximation, and show great disparity
between different waveguide QED setups. As a comparison, the step-like growth
of instantaneous decay rates in the retardation-only picture has also been
shown. All of these theoretical pictures predict the same collective behavior
in the long time limit. From a phenomenological standpoint, we observe that the
atomic superradiance exhabits significant directional property. In addition,
the subradiant photons feature prolonged oscillation in the early stage of
collective radiance, where the energy is exchanged remarkably between giant
emitters and the field. Our results might be probed in state-of-art waveguide
QED experiments, and fundamentally broaden the fields of collective emission in
systems with giant atoms.
