Electromagnetically induced transparency and optical pumping in the hyperfine Paschen-Back regime

We report spectroscopy experiments of rubidium vapor in a high magnetic field under conditions of electromagnetically induced transparency (EIT) and optical pumping. The 1.1-T static magnetic field decouples nuclear and electronic spins and shifts each magnetic state via the Zeeman effect, allowing us to resolve individual optical transitions of the $D_2$ line in a Doppler-broadened medium. By varying the control laser power driving one leg of a spectrally isolated $\mathrm{\Lambda }$ system we tune the vapor from the EIT regime to conditions of Autler-Townes line splitting. The resulting spectra conform to simple three-level models demonstrating the effective simplification of the energetic structure. Further, we quantify the viability of state preparation via optical pumping on nuclear spin-forbidden transitions. We conclude that the “cleanliness” of this system greatly enhances the capabilities of quantum control in hot vapor, offering advantages in a broad variety of quantum applications plagued by spurious light-matter interaction processes, such as atomic quantum memories for light.