Cross-spectral analysis is widely used for weak-signal extraction due to its ability to suppress uncorrelated noise. The common frequency-correlated noise of the probe laser in different detection channels restricts the cross-spectral noise suppression and degrades sensitivity. We propose and experimentally demonstrate a dual-channel Rydberg heterodyne scheme based on asymmetric optical detuning. This method with cross-spectral density (CSD) processing reduces the interchannel probe-frequency noise correlation while preserving the common microwave-induced atomic response essential for signal coherence. Experimental results confirm that asymmetric detuning selectively suppresses laser-noise-induced coherence without degrading signal correlation and thus improves the signal-to-noise ratio (SNR). Compared with single-channel power spectral density (PSD) analysis, this method reduces the noise floor and improves the SNR by 12 dB for the resonant case and by 3.7 dB for the detuned case. These results provide a practical and readily implementable strategy for suppressing correlated technical noise in Rydberg heterodyne receivers, advancing the development of high-sensitivity electric-field metrology.
Cross-spectral analysis is widely used for weak-signal extraction due to its ability to suppress uncorrelated noise. The common frequency-correlated noise of the probe laser in different detection channels restricts the cross-spectral noise suppression and degrades sensitivity. We propose and experimentally demonstrate a dual-channel Rydberg heterodyne scheme based on asymmetric optical detuning. This method with cross-spectral density (CSD) processing reduces the interchannel probe-frequency noise correlation while preserving the common microwave-induced atomic response essential for signal coherence. Experimental results confirm that asymmetric detuning selectively suppresses laser-noise-induced coherence without degrading signal correlation and thus improves the signal-to-noise ratio (SNR). Compared with single-channel power spectral density (PSD) analysis, this method reduces the noise floor and improves the SNR by 12 dB for the resonant case and by 3.7 dB for the detuned case. These results provide a practical and readily implementable strategy for suppressing correlated technical noise in Rydberg heterodyne receivers, advancing the development of high-sensitivity electric-field metrology.
Abstract Increasing the number of atoms that interact with microwave fields represents a promising strategy for enhancing the sensitivity of Rydberg atom-based superheterodyne receivers. Nevertheless, the practical implementation of this approach is impeded by adverse effects such as excitation saturation of Rydberg atoms and power broadening. Here, we demonstrate enhanced microwave field measurements based on two specific velocity groups of atoms, simultaneously addressed by dual-channel probe beams in a Sagnac loop interferometer. The application of resonance detuning in two-photon excitation enables selective addressing of atoms moving along the beam direction, thereby significantly mitigating atomic transit noise. At 7.97 GHz, our method yields a 3 dB improvement in signal-to-noise ratio (SNR), achieving a sensitivity of 10.7 nV⋅cm −1 ⋅Hz −1/2 . This approach offers a viable pathway to further improve the sensitivity of Rydberg atom-based microwave electrometers.
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.
We conduct a theoretical investigation into the impacts of local microwave electric field frequency detuning, laser frequency detuning, and transit relaxation rate on enhancing heterodyne Rydberg atomic receiver sensitivity. To optimize the output signal amplitude given the input microwave signal, we derive the steady-state solutions of the atomic density matrix. Numerical results show that laser frequency detuning and local microwave electric field frequency detuning can improve the system detection sensitivity, which can help the system achieve extra sensitivity gain. It also shows that the heterodyne Rydberg atomic receiver can detect weak microwave signals continuously over a wide frequency range with the same sensitivity or even more sensitivity than the resonance case. To evaluate the transit relaxation effect, a modified Liouville equation is used. We find that the transition relaxation rate increases the time it takes to reach steady state and decreases the sensitivity of the system detection.
This paper investigates the transfer of probe or coupling light modulation interference to density matrix elements in a four-level heterodyne Rydberg system. By combining the density matrix dynamical equations with power spectral density (PSD) analysis, we derive analytical solutions to describe this phenomenon. Our results demonstrate that coherence in multi-level systems fundamentally enables this transfer mechanism, thereby increasing the system's noise floor and degrading microwave detection sensitivity. Building on these findings, we establish a sensitivity-noise-constraint relationship to suppress the influence of noise.
Rydberg atom, which exhibits a strong response to weak electric fields, is regarded as a promising atomic receiver to surpass the sensitivity of conventional receivers. However, its sensitivity is strongly limited by the noise coming from both classical and quantum levels, and how to enhance it significantly remains challenging. In theory, we aim to optimize the laser array, highlighting the importance of coherence among microwave signals and the uniformity of laser beam power within the array, to enhance the signal-to-noise ratio (SNR) and elevate sensitivity to a new standard. To enhance practical application mobility and integration, we propose two optimization schemes: a six-port fiber-coupled vapor cell probe array and cascaded diffraction gratings. We maintain steady MW signal coherence in the laser array by using identical vapor cells and positioning the probe lasers on the incident wave’s equal phase plane. Our findings reveal that the wavefront phase difference for the six-port fiber-coupled vapor cell array is 10°, while the cascaded diffraction gratings show a 16° difference, with laser intensity uniformity reaching 90.4%. In our experiment, a 4.6-dB SNR enhancement was achieved by utilizing the cascaded diffraction gratings to generate2×2probe laser arrays compared to the performance of a laser beam, which can be enhanced further just by adding more laser beams. In particular, a2×2laser array experimental verification yielded19nv/cm/Hz@8.57 GHz. More importantly, the intermediate signals of the laser array maintain coherence. Therefore, SNR improvement is allowed even in detecting weak target signals amid strong noise and clutter. The results could offer an avenue for the design and optimization of ultrahigh-sensitivity Rydberg atomic receivers and promote applications in cosmology, meteorology, communication, and MW quantum technology.
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.