  The dynamics of an atomic few-level system can depend on the phase of driving
fields coupled to the atom if certain conditions are satisfied. This is of
particular interest to control interference effects, which can alter the system
properties considerably. In this article, we discuss the mechanisms of such
phase control and interference effects in an atomic three-level system in
$\Lambda$ configuration, where the upper state spontaneously decays into the
two lower states. The lower states are coupled by a driving field, which we
treat as quantized. This allows for an interpretation on the single photon
level for both the vacuum and the driving field. By analyzing the system
behavior for a driving field initially in non-classical states with only few
Fock number states populated, we find that even though the driving field is
coupled to the lower states only, it induces a multiplet of upper states. Then
interference occurs independently in three-level subsystems in $V$
configuration, each formed by two adjacent upper states and a single dressed
lower state.
