Universal quantum storage with spin wave in a ring array of nuclear spins

We propose a novel solid state based protocol to implement the universal quantum storage for electronic spin qubit. The quantum memory in this protocol is the magnons in the ring array of nuclei in a quantum well. We show that the quantum information carried by an arbitrary state of the electronic spin can be coherently mapped onto the magnon excitations in the spin wave quantum memory. With appropriate external control, the stored quantum state in quantum memory can be read out reversibly. We also explore the novel mechanism of quantum decoherence due to the inhomogeneous couplings between the electronic spin and the nuclear spins