Storage and retrieval of light pulses in atomic media with “slow” and “fast” light

We report experimental evidence that light storage, understood as the controlled release of a light pulse by an atomic sample dependent on the past presence of a writing pulse, is not restricted to small-group-velocity media but can also occur in a negative-group-velocity medium. We present a numerical modeling in close agreement with our observations and a simple physical picture applicable to light storage experiments in both “slow” and “fast” light media.

Figure 1

Upper: Level scheme and experimental setup. Center: observed signals for the probe field intensity transmission. Trace $a$ transition $5S_{1∕2}(F=2)\to 5P_{1∕2}(F^{\prime }=1)$ of ${}^{87}\mathrm{Rb}$ with Gaussian probe pulse; dashed, Gaussian envelope of transmitted probe pulse without dark interval. Trace $b$: Same transition; square probe pulse. Trace $c$: Transition $5S_{1∕2}(F=2)\to 5P_{3∕2}(F^{\prime }=3)$ of ${}^{87}\mathrm{Rb}$; square probe pulse. Bottom: timing sequence for the drive and probe fields.

Figure 2

Dotted (dashed): drive (probe) time sequence. Trace $a$: Calculated transmitted probe field intensity for the transition $5S_{1∕2}(F=2)\to 5P_{1∕2}(F^{\prime }=1)$ of ${}^{87}\mathrm{Rb}$. Trace $b$: Same for the transition $5S_{1∕2}(F=2)\to 5P_{3∕2}(F^{\prime }=3)$. Parameters (see [14]): ${\Omega }_D∕\Gamma =0.3$ (trace $a$), ${\Omega }_D∕\Gamma =0.6$ (trace $b$), ${\Omega }_D∕{\Omega }_P=2$, $\gamma ∕\Gamma ={10}^{-3}$, $\alpha =8$, $B=0$ (${\Omega }_D$ and ${\Omega }_P$ are the drive and probe field Rabi frequencies).

Figure 3

Basic level schemes for the light-atom interaction. White arrow, applied field; dashed arrow, spontaneous emission; solid arrow, stimulated Raman emission; curved arrow, ground-state coherence. (a) Incoherent optical pumping, (b) optical pumping with coherence, and (c) generalization of (a) for two levels with Zeeman degeneracy.