Photon echo quantum memories in inhomogeneously broadened two level   atoms
  Here we propose a solid-state quantum memory that does not require spectral holeburning, instead using strong rephasing pulses like traditional photon echo techniques. The memory uses external broadening fields to reduce the optical depth and so switch off the collective atom-light interaction when desired. The proposed memory should allow operation with reasonable efficiency in a much broader range of material systems, for instance Er3+ doped crystals which have a transition at 1.5 um. We present analytic theory supported by numerical calculations and initial experiments. 
D. L. McAuslan, P. M. Ledingham, W. R. Naylor, S. E. Beavan, M. P.   Hedges, M. J. Sellars, and J. J. Longdell
quant-ph