Single-Photon-Level Atomic Frequency Comb Storage in Room Temperature Alkali Vapour

Abstract

We have demonstrated the coherent storage and retrieval of single-photon-level light using the atomic frequency comb protocol in a room temperature rubidium vapour. 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 $5^2$P${}_{3/2}$ excited state. Weak coherent states of average photon number $\hat{I}{¼}_{\mathrm{in}}=0.083(5)$ are stored with pre-programmed recall time of $7.5$ns with an efficiency of $\hat{I}{\cdot }_{\text{AFC}}=6.59(5)\%$, while two temporally distinct modes have been stored and recalled with $\hat{I}{\cdot }_{\text{AFC}}=2.6(1)\%$, allowing for time-bin qubit storage. Finally, the efficiency is observed to be independent of the input pulse polarisation, paving the way for polarisation qubit storage.

17 pages, 9 figures