  The three-pulse photon echo is a well-known technique to store intense light
pulses in an inhomogeneously broadened atomic ensemble. This protocol is
attractive because it is relatively simple and it is well suited for the
storage of multiple temporal modes. Furthermore, it offers very long storage
times, greater than the phase relaxation time. Here, we consider the
three-pulse photon echo in both two- and three-level systems as a potential
technique for the storage of light at the single-photon level. By explicit
calculations, we show that the ratio between the echo signal corresponding to a
single-photon input and the noise is smaller than one. This severely limits the
achievable fidelity of the quantum state storage, making the three-pulse photon
echo unsuitable for single-photon quantum memory.
