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arXiv:2502.20792 · Optics Express

Cavity-enhanced Rydberg atomic superheterodyne receiver

Yukang Liang, Qinxia Wang, Zhi‐Hui Wang, Shijun Guan, Pengfei Yang, Yuchi Zhang, Jun He, Pengfei Zhang, Gang Li, Tiancai Zhang

Published Mar 4, 2025• 7 citations
arXivHTMLPDF

Abstract

High-sensitivity measurements of the microwave electric field are important in applications of communication and metrology. The sensitivity of traditional Rydberg superheterodyne receivers in free space is effectively determined by the signal-to-noise ratio (SNR), which is often considered equivalent to sensitivity in practical sensing applications. In this work, we demonstrate a cavity-enhanced receiver, where an optical cavity significantly amplifies the interaction between the probe light and cesium atoms, which substantially improves the signal-to-noise ratio via enhancing the expansion coefficient κ . Here, κ is the edge slope of the single peak obtained by fitting the double-peak EIT-AT spectrum, characterizing the response of the probe light to the frequency detuning of the coupling laser. The sensitivity is thus boosted by a factor of approximately 19 dB. This study highlights the pivotal role of optical cavities in advancing Rydberg-based detection systems, offering a promising approach for high-sensitivity microwave electric field measurements.

DOI
10.1364/oe.552016

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High-sensitivity measurements of the microwave electric field are important in applications of communication and metrology. The sensitivity of traditional Rydberg superheterodyne receivers in free space is effectively determined by the signal-to-noise ratio (SNR), which is often considered equivalent to sensitivity in practical sensing applications. In this work, we demonstrate a cavity-enhanced receiver, where an optical cavity significantly amplifies the interaction between the probe light and cesium atoms, which substantially improves the signal-to-noise ratio via enhancing the expansion coefficient κ . Here, κ is the edge slope of the single peak obtained by fitting the double-peak EIT-AT spectrum, characterizing the response of the probe light to the frequency detuning of the coupling laser. The sensitivity is thus boosted by a factor of approximately 19 dB. This study highlights the pivotal role of optical cavities in advancing Rydberg-based detection systems, offering a promising approach for high-sensitivity microwave electric field measurements.
Measurement sensitivity is crucial for the practical application of Rydberg atomic microwave superheterodyne receiver systems in communication, radar, and navigation. Based on laser-atom-microwave interaction mechanisms, the influence of laser powers and local-oscillator (LO) microwave field intensity on measurement sensitivity is systematically studied in this paper. Measurement sensitivity is analyzed through electromagnetically induced transparency (EIT) spectral characteristics, specifically EIT amplitude and full-width-half-maximum (FWHM),larger amplitudes and narrower FWHM indicate improved signal-to-noise ratios. For a 60D-state Rydberg atomic system with fixed probe and coupling laser beam waists (800 µm and 875 µm), optimal parameters are determined: probe laser power of 60 µW(Rabi frequency: 2π×7.02 MHz), coupling laser power of 40 mW (Rabi frequency: 2π×0.66 MHz), and LO microwave Rabi frequency of 2π×8.34 MHz. Experimental results demonstrate a 4.6 dB sensitivity enhancement, advancing from −137.5dBm/Hz to −142.1 dBm/Hz at 3.21 GHz microwave field. This improvement is attributed to precise alignment of laser-atom and microwave-atom interactions, bridging the gap toward quantum sensitivity limits.
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.
High-precision spectra of Rydberg atoms are of significance in studying the interaction between Rydberg atoms, the energy level structure of Rydberg atom, and the precision measurement of the electromagnetic field. To enhance the measurement sensitivity, it is necessary to achieve the high contrast, high signal-to-noise ratio, and narrow linewidth of the spectra of the Rydberg atoms. In this work, the cavity-enhanced spectra of Rydberg atoms are studied theoretically and experimentally. Comparing with the free-space spectra of Rydberg atoms, the contrast and the signal-to-noise ratio are enhanced by 11.5 times, with the linewidth unchanged. Under the condition of two-photon resonance, both the electro-magnetically induced transparency and the double-resonance optical-pumping process can suppress the absorption of the probe laser, thereby improving the impedance matching of the cavity. As the intracavity probe laser intensity turns stronger, the contrast and signal-to-noise ratio can be improved further, and the improvement depends on the transmission of the probe laser through the atom vapor. It is expected that the contrast and signal-to-noise ratio can be improved by a factor of 23 through optimizing the temperature of the cesium atom vapor. This work provides an important reference for improving the contrast of the spectra of Rydberg atoms and the sensitivity of Rydberg-based precision measurements.
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.
Rydberg atom-based microwave (MW) atomic receiver is regarded as a promising atomic receiver to surpass the sensitivity of conventional receivers. This article proposes a tunable Fabry-Perot (FP) cavity that locally enhances the MW electric (E) field to improve measurement sensitivities. This FP cavity includes a 0.9947 reflection coefficient periodic metal slit structure and a reflective plate. In our experiment, 21-dB signal-to-noise ratio (SNR) enhancement is achieved by utilizing the FP cavity. Ultimately, the atomic receiver loaded with a FP cavity provides a sensitivity of$ \mathbf {5 \mathbf {nv/cm/\sqrt {Hz}}}@8.57GHzthatisthemostadvancedsensitivityknownbasedon@8.57 GHz that is the most advanced sensitivity known based on@8.57GHzthatisthemostadvancedsensitivityknownbasedon\mathbf {^{133}\textrm {Cs}}resonanttransitionresonant transitionresonanttransition\mathbf {|44D_{5/2}\rangle \rightarrow |45P_{3/2}\rangle }$. Since the FP cavity is different from the traditional closed cavity and split-ring resonance mechanism, a large enhancement tunable frequency bandwidth of 4.8–12.2 GHz can be achieved by adjusting the plate spacing. In addition, the FP cavity solves the direct coupling between the electromagnetic wave and the resonator in the X-band, which provides mobility and flexibility. We take all the vapor cell wall’s refractive index and metal reflections into account as the resonance-based system is more sensitive to errors.
In recent years, electric field measurement techniques based on Rydberg atoms have shown unique advantages in high sensitivity and wideband applications and miniaturization. The Rydberg atom receiver senses the electromagnetic signal using the quantum coherence effect, which overcomes the inherent defects of traditional electronic receivers in terms of thermal noise, insertion loss of microwave devices, and the use of wavelength-dependent antennas, thus providing the Rydberg atomic receivers the potential to become the next generation of microwave receivers. For some particular application scenarios such as radar and communication, superheterodyne reception is a critical technical approach, and the linear dynamic range is an essential factor in evaluating the performance of the superheterodyne receivers. It is challenging to promote the Rydberg atomic receiver without figuring out the influence of system parameters on the linear dynamic range. This paper starts with the response mechanism of the Rydberg atomic superheterodyne receiver, and a theoretical model is established to simulate the atom-microwave responses. Then the harmonics' generation mechanism is discussed, and the atomic linear dynamic range under different probe light Rabi frequencies is studied further. Furthermore, a method to evaluate the antiblocking performance of the system is proposed. This work is expected to provide theoretical guidance for the design and performance optimization of the Rydberg atomic superheterodyne receiver.