Initialization protocol for efficient quantum memories using resolved hyperfine structure

We describe a quantum memory spectral preparation strategy that optimizes memory efficiency and bandwidth in materials such as Er3+167:Y2SiO5 in a high-field regime, where the hyperfine structure is resolved. We demonstrate the method in Er3+167:Y2SiO5 by preparing spectrally isolated 18-dB-absorbing features on a <1 dB background. Using these features we create an atomic frequency comb and show a quantum storage of 200-ns pulses with 22% efficiency, limited by the background absorption which arises from laser instability. We describe the experimental improvements needed to reach the material limits: O(1)-s spin-state storage, O(100)MHz bandwidth, and >90% efficiency.