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In an isotopically pure 143 Nd 3+: Y 7 LiF 4 crystal we demonstrate an optical quantum memory on a single photon level using the atomic frequency comb memory protocol. Using weakened laser pulses we demonstrate storage efficiency of 6. 5% with the storage time of 60 ns and signal to noise ratio of around 3.
Ахмеджанов et al. (Tue,) studied this question.