  We study the transfer dynamics of non-classical fluctuations of light to the
ground-state collective spin components of an atomic ensemble during a pulsed
quantum memory sequence, and evaluate the relevant physical quantities to be
measured in order to characterize such a quantum memory. We show in particular
that the fluctuations stored into the atoms are emitted in temporal modes which
are always different than those of the readout pulse, but which can
nevertheless be retrieved efficiently using a suitable temporal mode-matching
technique. We give a simple toy model - a cavity with variable transmission -
which accounts for the behavior of the atomic quantum memory.
