Multimode Memories in Atomic Ensembles

The ability to store multiple optical modes in a quantum memory allows for increased efficiency of quantum communication and computation. Here we compute the multimode capacity of a variety of quantum memory protocols based on light storage in ensembles of atoms. We find that adding a controlled inhomogeneous broadening improves this capacity significantly.

Figure 1

(a) An incident signal field is mapped to a stationary spin wave inside an ensemble quantum memory. (b) The multimode scaling of unbroadened ensemble memories (solid line) alongside the TCRIB (dashed line) and LCRIB (dotted line) protocols, with a threshold $\theta =70\%$.

Figure 2

(a) The multimode scaling for the Raman protocol with an applied broadening (solid line) and without (dashed line). Here we set $\Omega (\tau )=\sqrt{10d}\gamma e^{-(10\gamma \tau {)}^2}$ and $\Delta =\sqrt{90d}\gamma$. (b) The capacity of AFC with several different numbers of comb teeth, indicated by the numbers in the plot. We used a threshold $\theta =70\%$.