Single-photon-level atomic frequency comb storage in room temperature alkali vapor

We have demonstrated the coherent storage and retrieval of single-photon-level light using the atomic frequency comb protocol in a room temperature rubidium vapor. Velocity-selective optical pumping is used to prepare the comb within the F = 2 hyperfine ground state of rubidium, with the spacing between peaks coinciding with half the F = 2 − F = 3 hyperfine splitting of the 5 P 3 / 2 2 excited state. Weak coherent states of average photon number μ in = 0.083 ( 5 ) are stored with preprogrammed recall time of 7.5 ns with an efficiency of η AFC = 6.59 ( 5 ) % , while two temporally distinct modes have been stored and recalled with η AFC = 2.6 ( 1 ) % , allowing for time-bin qubit storage. Finally, the storage efficiency is observed to be independent of the input pulse polarization, satisfying a necessary condition for polarization qubit storage.