  Coherent manipulation of single-photon wave packets is essentially important
for optical quantum communication and quantum information processing. In this
paper, we realize controllable splitting and modulation of single-photon-level
pulses by using a tripod-type atomic medium. The adoption of two control beams
enable us to store one signal pulse into superposition of two distinct atomic
collective excitations. By controlling the time delay between the two control
pulses, we observe splitting of a stored wave packet into two
temporally-distinct modes. By controlling the frequency detuning of the control
beams, we observe both temporal and frequency-domain interference of the
retrieval signal pulses, which provides a method for pulse modulation and
multi-splitting of the signal photons.
