  The studies on quantum open system play key roles not only in fundamental
problems in quantum mechanics but also in quantum computing and information
processes. Here we propose a scheme to use a one dimensional coupling cavity
array (CCA) as an artificial electromagnetic environment of a two-level atom.
For a finite length of CCA, we find that after a turning time the population of
excited state deviates suddenly from the exponential decay. We show that
physically this phenomena corresponds to a transition from a naked atom decay
to a dressed state decay. We hope that our finding will promote the studies on
quantum system with a finite size environment.
