We propose a method to implement a quantum memory for light based on
ensembles of two-level atoms. Our protocol is based on controlled reversible
inhomogeneous broadening (CRIB), where an external field first dephases the
atomic polarization and thereby stores an incoming light pulse into collective
states of the atomic ensemble, and later a reversal of the applied field leads
to a rephasing of the atomic polarization and a reemission of the light. As
opposed to previous proposals for CRIB based quantum memories we propose to
only apply the broadening for a short period after most of the pulse has
already been absorbed by the ensemble. We show that with this procedure there
exist certain modes of the incoming light field which can be stored with an
efficiency approaching 100% in the limit of high optical depth and long
coherence time of the atoms. These results demonstrate that it is possible to
operate an efficient quantum memory without any optical control fields
