We present an experimental study of a Δ system in a room temperature, dilute sample of 85 Rb atoms. A Δ system in the D2 manifold of 85 Rb is formed by connecting the two lower hyperfine energy levels of a Λ system by a microwave drive field at 3.0357GHz. We show that when the Rabi frequency of a microwave drive field exceeds that of the optical probe field, a three-wave mixing nonlinear interaction is established. This nonlinear interaction changes the enhanced transmission of the optical probe to a deep absorption for a relative phase difference of π between all the three fields. We establish through our experiment and our numerical simulation, the phase-sensitive and nonlinear nature of the Δ system's response to the applied microwave and optical fields. Using this feature, we demonstrate a high-contrast microwave phase controlled switch for the optical probe field. In comparison with intensity and phase switching demonstrated with all-optical fields so far, our experiment opens up the possibility of obtaining the highest contrast optical switching with room temperature atoms.

We study phase-sensitive amplification of electromagnetically induced transparency in a warm 85 Rb vapor wherein a microwave driving field couples the two lower energy states of a Λ energy-level system thereby transforming into a ∆ system. Our theoretical description includes effects of groundstate coherence decay and temperature effects. In particular, we demonstrate that driving-field enhanced electromagnetically induced transparency is robust against significant loss of coherence between ground states. We also show that for specific field intensities, a threshold rate of groundstate coherence decay exists at every temperature. This threshold separates the probe-transmittance behavior into two regimes: probe amplification vs. probe attenuation. Thus, electromagnetically induced transparency plus amplification is possible at any temperature in a ∆ system.

Coherent microwave-to-optical conversion by three-wave mixing in a room temperature atomic system.