Storage and Retrieval of a Microwave Field in a Spin Ensemble
  We report the storage and retrieval of a small microwave field from a superconducting resonator into collective excitations of a spin ensemble. The spins are nitrogen-vacancy centers in a diamond crystal. The storage time of the order of 30 ns is limited by inhomogeneous broadening of the spin ensemble. 
Y. Kubo, I. Diniz, A. Dewes, V. Jacques, A. Dreau, J.-F. Roch, A.   Auffeves, D. Vion, D. Esteve and P. Bertet
cond-mat.mes-hall quant-ph