  We examine a quantum memory scheme based on controllable dephasing of atomic
coherence of a non-resonant, inhomogeneously broadened Raman transition. We
show that it generalizes the physical conditions for time-reversible
interaction between light and atomic ensembles from weak to strong fields and
from linear to non-linear interactions. We also develop a unified framework for
different realizations exploiting either controlled reversible inhomogeneous
broadening or atomic frequency combs, and discuss new aspects related to
storage and manipulation of quantum states.
