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

We demonstrate a multiphoton Rydberg dark resonance where a Lambda-system is coupled to a Rydberg state. This 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 nd_{5/2} Rydberg state in 87Rb (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 V/cm. We show that, even when photons with different wavevectors are involved, the resonance can be Doppler-free. Applications in electro-optic switching and photonic phase gates are discussed.