Figure 1

(a) The atomic structure for the proposed cascade emission scheme involving excitation by pumps I and II. Pump II and the signal photons lie in the telecommunication wavelength range when a suitable level of orbital angular momentum $L=0$ or $L=2$ is used as level $|d⟩$. For atomic rubidium, the signal wavelength is $1.32\mu \mathrm{m}$ ($6s_{1/2}\to 5p_{1/2}$ transition), $1.37\mu \mathrm{m}$ $6s_{1/2}\to 5p_{3/2}$ transition), $1.48\mu \mathrm{m}$ ($4d_{3/2(5/2)}\to 5p_{1/2}$ transition), $1.53\mu \mathrm{m}$ ($4d_{3/2(5/2)}\to 5p_{3/2}$ transition). For atomic cesium, the signal wavelength is $1.36\mu \mathrm{m}$ ($7s_{1/2}\to 6p_{1/2}$ transition), $1.47\mu \mathrm{m}$ ($7s_{1/2}\to 6p_{3/2}$ transition). For Na and K the corresponding wavelengths are in the $1.1–1.4\mu \mathrm{m}$ range. (b) Schematic of experimental setup based on ultracold ${}^{85}\mathrm{Rb}$ atomic gas. For ${\lambda }_s=776\mathrm{nm}$, phase matching results in the angles ${\epsilon }^{\prime }\approx \epsilon \approx 1°$, while for ${\lambda }_s=1.53\mu \mathrm{m}$, ${\epsilon }^{\prime }\approx 2\epsilon \approx 2°$. $P_1$ and $P_2$ are polarizers; $D1$ and $D2$ are detectors.Reuse & Permissions

Figure 2

(a) Count rate proportional to the signal-idler intensity correlation function $G_{\mathrm{si}}$ as a function of signal-idler delay $\tau$, $|d⟩=|5d_{5/2},F=4⟩$. The quantum beats are associated with 120 MHz hyperfine splitting, $F=3$ and 4, of the $5p_{3/2}$ level [14]. The solid curve is a fit of the form $\beta +A\exp (-t/\alpha ){sin}^2(\pi \Omega t)$, where $\beta =63$, $A=2972$, $\alpha =11\mathrm{ns}$, and $\Omega =117\mathrm{MHz}$ are adjustable parameters. (b) Same as (a), but for $|d⟩=|5d_{5/2},F=5⟩$. Since this state can only decay though the $F=4$ component of the $5p_{3/2}$ level, there are no quantum beats. The solid curve is an exponential fit with decay time of 3.2 ns. (c) The measured decay time vs the inverse measured optical thickness. (d) Measured coincidence fringes for ${\theta }_s=45°$ (red diamonds) and ${\theta }_s=135°$ (blue circles). The solid curves are fits based on Eqs. (1, 2), with $\cos \chi =1/\sqrt{5}$.Reuse & Permissions

Figure 3

(a) Same as Figs. 2a, 2b, but for $|d⟩=|4d_{5/2},F=5⟩$. The solid curve is an exponential fit with decay time of 6.7 ns. (b) Measured coincidence fringes for ${\theta }_i=45°$ (red diamonds) and ${\theta }_i=135°$ (blue circles). The solid curves are fits based on Eqs. (1, 2), with $\cos \chi =1/\sqrt{5}$.Reuse & Permissions

Figure 4

Efficiency of storage and subsequent retrieval of a coherent idler field with decay time of 6 ns in an auxiliary atomic ensemble, obtained by numerical integration of the Maxwell-Bloch equations [12, 18, 23]. This efficiency is independent of the storage time as long as the latter is much shorter than the atomic memory time. The control field Rabi frequency is chosen to be $3/t_s$, and is turned off smoothly between 10 and 30 ns after the idler enters the auxiliary ensemble. For these parameters the maximum efficiency is limited since the spectral width of the idler pulse is much wider than the transparency window. However, increased storage efficiency is found using larger control field intensities [12].Reuse & Permissions