Effects of static dc electric-field orientation on two-photon Rydberg electromagnetically induced transparency

We examine the influence of a static dc electric field on Electromagnetically Induced Transparency (EIT) resonances that involve highly excited Rydberg states. Our focus is on how these resonances are altered when the relative orientation between the laser polarization and the external electric field vectors are varied. We experimentally demonstrate characteristic variations in the amplitude of the Stark-split EIT resonances, which can be explained by the selection rules in various geometries. We also present a simplified semi-analytical model that closely resembles the experimental observations. We use these findings to obtain information about the spatially inhomogeneous electric field, produced by a biased wire, using EIT fluorescence measurements that agrees with the expected angular dependencies. These results suggest that simultaneous analysis of frequency shifts and amplitudes of Rydberg EIT resonances may enable vector electrometry of electrostatic fields, necessary for many quantum sensing applications.