Storage of multiple coherent microwave excitations in an electron spin ensemble

Abstract: We demonstrate the storage and retrieval of weak 10 GHz coherent excitations in distributed memories based on electron spin ensembles. Each excitation is phase encoded by a field gradient and the use of pulsed field gradients permits the stored excitations to be recalled in an arbitrary order. We have stored up to 100 weak microwave excitations in a spin ensemble and recalled them sequentially. We further demonstrate the use of a coupled nuclear spin, which can offer coherence times in excess of seconds, for even more robust storage.