Duda, CK; Ferguson, KR; Ahlefeldt, RL; Hedges, MP; Sellars, MJ
We studied the recall efficiency as a function of optical depth of rephased amplified spontaneous emission (RASE), a protocol for generating entangled light. The experiments were performed on the 3H4  1D2 transition in the rare-earth doped crystal Pr3+:Y2SiO5, using a four-level echo sequence between four hyperfine levels to rephase the emission. Rephased emission was observed for optical depths in the range of αL = 0.8 to 2.0 with a maximum rephasing efficiency of 14 % observed while incorporating spin storage. This efficiency is a significant improvement over the previously reported non-classical result but is well short of the predicted efficiency. We discuss the possible mechanisms limiting the protocol’s performance, and suggest ways to overcome these limits.