  The absorption of broadband photons in atomic ensembles requires either an
effective broadening of the atomic transition linewidth, or an off-resonance
Raman interaction. Here we propose a scheme for a quantum memory capable of
storing and retrieving ultrafast photons in an ensemble of two-level atoms by
using a propagation medium with a time-dependent refractive index generated
from aligning an ensemble of gas-phase diatomic molecules. The refractive index
dynamics generates an effective longitudinal inhomogeneous broadening of the
two-level transition. We numerically demonstrate this scheme for storage and
retrieval of a weak pulse as short as 50 fs, with a storage time of up to 20
ps. With additional optical control of the molecular alignment dynamics, the
storage time can be extended about one nanosecond leading to time-bandwidth
products of order $10^4$. This scheme could in principle be achieved using
either a hollow-core fiber or a high-pressure gas cell, in a gaseous host
medium comprised of diatomic molecules and a two-level atomic vapor at room
temperature.
