  Off-resonant Raman interaction of a single-photon wave packet and a classical
control field in an atomic medium with controlled refractive index is
investigated. It is shown that a continuous change of refractive index during
the interaction leads to the mapping of a single photon state to a
superposition of atomic collective excitations (spin waves) with different wave
vectors and visa versa. The suitability of refractive index control for
developing multichannel quantum memories is discussed and possible schemes of
implementation are considered.
