Photon-Echo Quantum Memory
  The future of long-distance quantum communication relies on the availability of quantum memory, i.e. devices that allow temporal storage of quantum information. We review research related to quantum state storage based on a photon-echo approach in rare earth ion doped crystals and glasses. 
W. Tittel (1), M. Afzelius (2), R. L. Cone (3), T. Chaneli\`ere (4),   S. Kr\"oll (5), S. A. Moiseev (6), and M. Sellars (7)...