Abstract
We experimentally study a broadband implementation of the atomic frequency comb (AFC) rephasing protocol with a cryogenically cooled ${{\rm Pr}^{3 +}}:{{\rm Y}_2}{{\rm SiO}_5}$ crystal. To allow for storage of broadband pulses, we explore a novel, to the best of our knowledge, regime where the input photonic bandwidth closely matches the inhomogeneous broadening of the material $(\sim 5 \;{\rm GHz})$, thereby significantly exceeding the hyperfine ground and excited state splitting $(\sim 10 \;{\rm MHz})$. Through an investigation of different AFC preparation parameters, we measure a maximum efficiency of 10% after a rephasing time of 12.5 ns. With a suboptimal AFC, we witness up to 12 rephased temporal modes.
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