  In this study, we investigated Rydberg atom-based microwave electrometry
using polarization spectroscopy in a room-temperature vapor cell. By measuring
Autler-Townes splitting in the electromagnetically induced transparency (EIT)
spectrum, we determined that the minimum measurable microwave electric field is
approximately five times lower than conventional EIT techniques. The results
are well reproduced by a full optical Bloch equation model, which takes into
account all the hyperfine levels involved. Subsequently, the EIT setup was used
to characterize a custom microwave cylindrical lens, which increases the field
at the focus by a factor of three, decreasing the minimum measurable microwave
electric field by the same amount. Our results indicate that the combination of
polarization spectroscopy and a microwave lens may enhance microwave
electrometry.
