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arXiv:2606.02669 · Optics Express

Sensitivity Enhancement of S-Band Rydberg Atom Microwave Receiver Using Resonant Cavity

Yipeng Xie, Xinbing Chen, Mingwei Lei, Meng Shi

physics.atom-phquant-phSubmitted Jun 1, 2026• Announced Jun 2, 2026• 0 citations
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Abstract

Rydberg atom-based microwave electric field sensing has attracted growing interest owing to its inherent advantages, such as absolute calibration, wideband operability, and compatibility with room-temperature devices. A critical bottleneck that limits sensitivity is the inefficient coupling between the Rydberg atoms and the incident microwave field, particularly when detecting weak signals propagating in free space. Here we propose and experimentally validate a scheme that integrates a horn antenna with a resonant microwave cavity to significantly improve this coupling for free-space signal reception in the S-band. Using a two-photon excitation scheme in a cesium vapor cell, we systematically characterize the sensing performance under three configurations: a bare cell, direct cavity injection, and a cavity coupled to a horn antenna that captures free-space microwave signals over a 1 m distance. In the antenna-coupled cavity configuration, we achieve an optimal sensitivity of 2.33 nV/cm/$\sqrt{\text{Hz}}$ at the receiving antenna, which corresponds to an enhancement of approximately 17.9 dB compared to the optimized bare vapor cell configuration. Our findings offer a practical and effective route to boost the sensitivity of Rydberg atomic sensors, facilitating their adoption in real-world microwave metrology and wireless communication applications where weak free-space electric fields must be reliably measured.

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11 pages, 4 figures

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Rydberg atom-based microwave electric field sensing has attracted growing interest owing to its inherent advantages, such as absolute calibration, wideband operability, and compatibility with room-temperature devices. A critical bottleneck that limits sensitivity is the inefficient coupling between the Rydberg atoms and the incident microwave field, particularly when detecting weak signals propagating in free space. Here we propose and experimentally validate a scheme that integrates a horn antenna with a resonant microwave cavity to significantly improve this coupling for free-space signal reception in the S-band. Using a two-photon excitation scheme in a cesium vapor cell, we systematically characterize the sensing performance under three configurations: a bare cell, direct cavity injection, and a cavity coupled to a horn antenna that captures free-space microwave signals over a 1 m distance. In the antenna-coupled cavity configuration, we achieve an optimal sensitivity of 2.33 nV/cm/Hz\sqrt{\text{Hz}}Hz​ at the receiving antenna, which corresponds to an enhancement of approximately 17.9 dB compared to the optimized bare vapor cell configuration. Our findings offer a practical and effective route to boost the sensitivity of Rydberg atomic sensors, facilitating their adoption in real-world microwave metrology and wireless communication applications where weak free-space electric fields must be reliably measured.
Abstract Developing microwave electric field sensing based on Rydberg atoms has received significant attention due to its unique advantages. However, achieving effective coupling between Rydberg atoms and the microwave electric field in the sensing process is a challenging problem that greatly impacts the sensitivity. To address this, we propose using a microwave resonant cavity to enhance the effective coupling between the Rydberg atoms and the microwave electric field. In our experiment, Rydberg atoms are prepared via a three-photon excitation scheme, and the electric fields are measured without and with a microwave cavity in which the vapor cell is placed inside, respectively. As a result, we achieved an 18 dB enhancement of power sensitivity by adding the cavity, which is an effective enhancement in electric field pulse signal detection. This experimental testing provides a promising direction for enhancing the sensitivity of Rydberg atomic electric field sensors and paves the way for their application in precision electric field measurements.
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