S., Deb, A

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 quantization of atomic angular momentum. Using an electromagnetically-induced transparency (EIT) sensing scheme, specific combinations of atomic terms are shown to give rise to universal, distinctive fingerprints in the detected optical fields upon rotating a linearly polarized RF field. Employing a dressed state picture, we identify two types of atomic angular momentum ladders that display strikingly disparate spectroscopic characteristics, including the distinctive absence or presence of a central spectral EIT peak. Our study adds important insights into the prospects of Rydberg atomic gases for quantum metrological electric field characterization including polarimetry. In particular, it calls into question prevailing interpretations of SI-traceable Rydberg atom electrometers.