Resonant Structures for Sensitivity Enhancement of Rydberg-Atom Microwave Receivers

Rydberg atoms at room temperature have been demonstrated as narrowband-sensitive receivers of incident microwave electric fields across MHz to THz frequencies. A comparison to conventional microwave receiver noise temperature suggests that some type of microwave field enhancement is required to make these atomic receivers competitive with or better than their conventional room-temperature electronic counterparts. This article presents a sensitivity analysis appropriate for the comparison of the two fundamentally different types of receivers, which relates the noise-equivalent temperature (NET), noise-equivalent field (NEF), and enhancement factor (F). Several methods for achieving enhancement are presented, and the design and performance of a resonant waveguide cavity method are presented in further detail. The experimental validation is performed at 10.22 GHz with a Rydberg-atom vapor cell enclosed in a
$X$
-band resonant cavity designed for field uniformity. The Rydberg-atom receiver with no enhancement has a sensitivity of
$23~\mu \text{V}$
/m
$(\mathrm {Hz})^{1/2}$
at room temperature. When the resonant cavity is introduced, the sensitivity improves to
$1.58~\mu \text{V}$
/m
$(\mathrm {Hz})^{1/2}$
, as predicted by the analysis. This corresponds to an LNA with a noise figure of 42.44 dB before enhancement and 19.23 dB after the enhancement is implemented.