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 2.2~GHz and a 3.6~GHz far-field excitation. Our measurements reveal a significant amplification of the EIT transparency 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 increases the signal-to-noise ratio (SNR) of the Rydberg RF receiver. This experimental validation highlights the potential of metamaterial-assisted quantum sensing to overcome the inherent bandwidth and sensitivity limitations of bare Rydberg receivers for a variety of applications, such as electromagnetic compatibility (EMC) testing, quantum radar, and wireless communications.