Experimental Sensitivity Enhancement of a Quantum Rydberg Atom-Based RF Receiver with a Metamaterial GRIN Lens

We experimentally demonstrate enhanced sensitivity of an atom-based Rydberg radio frequency (RF) receiver integrated with a gradient refractive index (GRIN) Luneburg-type metamaterial lens. By analyzing the electromagnetically induced transparency (EIT) effect in Cesium vapor, we compare receiver performance with and without the GRIN lens under a 2.2GHz and a 3.6GHz far-field excitation. Our measurements reveal a significant amplification of the EIT window when the lens is introduced, consistent with the theoretical prediction that the local E-field enhancement at the vapor cell reduces the minimum detectable electric field and improves the microwave electric field measurement sensitivity of the Rydberg atom-based RF receiver over an ultrawide bandwidth of the lens. This experimental validation demonstrates the potential of metamaterial-enhanced quantum RF sensing for a wide range of applications, such as electromagnetic compatibility (EMC) testing, quantum radar, and wireless communication.

💡 Research Summary

This paper presents a novel approach to boost the sensitivity of a Rydberg‑atom‑based radio‑frequency (RF) receiver by integrating a passive gradient‑index (GRIN) metamaterial lens of the Luneburg type. Conventional atom‑based RF sensors exploit electromagnetically induced transparency (EIT) in hot alkali vapors, but their practical sensitivity is limited by Doppler broadening, thermal noise, and the relatively weak interaction between the incident microwave field and the atomic transition dipole. Prior attempts to enhance the field—such as split‑ring resonators, Fabry‑Perot cavities, or interferometric schemes—either introduce spurious emissions, are narrowband, or require complex, costly hardware.

The authors therefore design a broadband, low‑loss, non‑resonant GRIN lens that focuses planar microwave wavefronts onto the centre of the vapor cell. The lens follows the Luneburg refractive‑index profile n(r)=√