Electro-optic control of atom-light interactions using Rydberg dark-state polaritons

We demonstrate a multiphoton Rydberg dark resonance where a $\ensuremath{\Lambda}$ system is coupled to a Rydberg state. This $\mathcal{N}$-type level scheme combines the ability to slow and store light pulses associated with long-lived ground-state superpositions with the strongly interacting character of Rydberg states. For the $n{d}_{5/2}$ Rydberg state in $^{87}\text{R}\text{b}$ (with $n=26$ or 44) and a beam size of 1 mm, we observe a resonance linewidth of less than 100 kHz in a room-temperature atomic ensemble limited by transit-time broadening. The resonance is switchable with an electric field of order $1\text{ }\text{V}\text{ }{\text{cm}}^{\ensuremath{-}1}$. Applications in electro-optic switching and photonic phase gates are discussed.