Abstract
Rydberg atoms efficiently link photons between the radio-frequency (RF) and optical domains. They furnish a medium in which the presence of an RF field imprints on the transmission of a probe laser beam by altering the coherent coupling between atomic quantum states. The immutable atomic energy structure underpins quantum-metrological RF field measurements and has driven intensive efforts to realize inherently self-calibrated sensing devices. Here we investigate spectroscopic signatures owing to the angular momentum quantization of the atomic states utilized in an electromagnetically-induced transparency (EIT) sensing scheme for linearly-polarized RF fields. Specific combinations of atomic terms are shown to give rise to universal, distinctive fingerprints in the detected optical fields upon rotating the RF field polarization. Using a dressed state picture, we identify two types of angular momentum ladders that display strikingly disparate spectroscopic signatures, including the absence or presence of a central spectral EIT peak. We verify our predicted complementary response in rubidium vapour cell experiments and through density matrix calculations. Our study adds important insights into the prospects of Rydberg atomic polarimetry for quantum metrological electric field characterization.