Extraction of Effective Electromagnetic Material Properties for Rydberg Electrometer Vapor Cells from 10-300 MHz
Quantum sensors often consist of packaging, such as dielectric-based vapor cells and metallic electrodes, that reduces and spatially alters the locally observed electromagnetic fields. These effects have been well studied in the optical regime, and even in the RF regime over a few GHz. However, there have been few studies in the electrically small regime below 1 GHz. In order to account for or remove the effects of the packaging, more studies are needed across a broad range of frequencies. This paper reports on the complex permittivity and conductivity of several commercially available vapor cells used for Rydberg electric field sensing from 10-300 MHz. A new method using a stripline transmission measurement was performed and full wave electromagnetics modeling was used to extract the effective dielectric constitutive parameters from the vapor cells. Additionally, the field reduction inside the vapor cell is reported, and published atomic measurements of the electric field are used to further validate the results presented here. Several observations were made from the measurements, such as the frequency dependencies of the RF dispersion and absorption. Applications of this technique include making precise numerical field corrections or physically designing a more optimal vapor cell via coatings, material changes, or geometric changes to improve field strength and uniformity.