Spin wave based quantum storage of electronic spin with a ring array of   nuclear spins
  We propose a solid state based protocol to implement the universal quantum storage for electronic spin qubit. The quantum memory in this scheme is the spin wave excitation in the ring array of nuclei in a quantum dot. We show that the quantum information carried by an arbitrary state of the electronic spin can be coherently mapped onto the spin wave excitations or the magnon states. With an appropriate external control, the stored quantum state in quantum memory can be read out reversibly. We also explore in detail the quantum decoherence mechanism due to the inhomogeneous couplings between the electronic spin and the nuclear spins. 
Y. D. Wang, Y. Li, Z. Song and C. P. Sun