  In the framework of open quantum systems, we study the dynamics of a static
polarizable two-level atom interacting with a bath of fluctuating vacuum
electromagnetic field and explore under which conditions the coherence of the
open quantum system is unaffected by the environment totally. For both a
single-qubit and two-qubit systems, we find that the quantum coherence can not
be protected from noise when the atom interacts with a non-boundary
electromagnetic field. However, with the presence of a boundary, the dynamical
conditions for the insusceptible of quantum coherence are fulfilled only when
the atom is close to the boundary and is transversely polarizable. Otherwise,
the quantum coherence can only be protected in some degree in other polarizable
direction.
