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arXiv:2605.08535 · Applied Physics Letters

Microwave Power-to-Frequency Transduction via Injection Pulling of a Self-Sustained Oscillator for Rydberg Superheterodyne Sensing

Darmindra Arumugam

quant-phSubmitted May 8, 2026• Announced May 12, 2026• 0 citations
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Abstract

A Rydberg superheterodyne sensing architecture is demonstrated in which a self-sustained oscillator (SSO) serves as a dynamically perturbed local oscillator (LO) for microwave detection. The SSO is realized by a phase-controlled radio-frequency (RF) feedback loop coupled to a transverse electromagnetic (TEM) cavity containing a Rydberg vapor cell. The system operates near 5.49 GHz using a cesium ladder scheme with an 852 nm probe and 510 nm coupling laser addressing the 6S to 6P to 49D transition, with microwave coupling to the 50P state. Injection of a microwave signal pulls the SSO frequency via nonlinear dynamics, converting input power into a measurable frequency shift read out optically as a Rydberg probe intermediate-frequency (IF) signal. The response follows Adler-type injection-pulling behavior, with continuous IF tuning with input power. A peak responsivity of 35 kHz/dB is observed, with enhanced sensitivity near synchronization. These results demonstrate power-to-frequency transduction using a dynamically perturbed LO combined with Rydberg atomic readout.

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A Rydberg superheterodyne sensing architecture is demonstrated in which a self-sustained oscillator (SSO) serves as a dynamically perturbed local oscillator (LO) for microwave detection. The SSO is realized by a phase-controlled radio-frequency (RF) feedback loop coupled to a transverse electromagnetic (TEM) cavity containing a Rydberg vapor cell. The system operates near 5.49 GHz using a cesium ladder scheme with an 852 nm probe and 510 nm coupling laser addressing the 6S to 6P to 49D transition, with microwave coupling to the 50P state. Injection of a microwave signal pulls the SSO frequency via nonlinear dynamics, converting input power into a measurable frequency shift read out optically as a Rydberg probe intermediate-frequency (IF) signal. The response follows Adler-type injection-pulling behavior, with continuous IF tuning with input power. A peak responsivity of 35 kHz/dB is observed, with enhanced sensitivity near synchronization. These results demonstrate power-to-frequency transduction using a dynamically perturbed LO combined with Rydberg atomic readout.
Microwave power-to-frequency transduction is demonstrated using the emergent oscillation frequency of a magnetically initiated Rydberg dissipative time crystal (DTC). In a room-temperature 87Rb vapor, a ~14 G magnetic field establishes a self-sustained DTC near 21 kHz, while a near-resonant 8.325 GHz field coupling the 63D3/2 to 64P3/2 manifold continuously shifts the autonomous oscillation frequency. The resulting field-to-frequency transfer function is strongly nonlinear, with a total fundamental-frequency excursion of ~6.7 kHz and peak responsivity approaching 1 kHz/(mV/cm). The nonlinear transition is substantially steeper than a simple quadratic saturation response and is captured by a self-consistent mean-field picture in which microwave-driven Rydberg-population redistribution modifies the collective resonance condition. Higher DTC harmonics preserve the same normalized transfer function while exhibiting approximately linear growth of absolute responsivity with harmonic order. These results establish an intrinsic many-body atomic route to RF amplitude-to-frequency conversion, enabling continuous frequency-domain sensing through an emergent atomic frequency without an externally engineered RF feedback oscillator, repeated optical spectral scans, or resolved Autler Townes splitting.
We propose and investigate a Rydberg atom sensor based on a loop-level structure, which utilizes the eigenfrequencies of the energy levels as a reference. This design eliminates the need for the local oscillator (LO) electric field required in the traditional superheterodyne structure while maintaining a linear relationship between the readout signal and the microwave (MW) electric field to be measured, along with exhibiting significantly lower harmonic distortion. For experimental validation, we implemented a cesium atomic system based on the loop five-level structure. The system achieved a sensitivity of 62 nVcm -1 Hz -1/2 and maintained 30 dB of harmonic suppression even near the nonlinear operational region under the strong electric field, which is approximately 20 dB higher than that of the superheterodyne structure. This work demonstrates that loop-level-based atomic sensors enable high-sensitivity and wide-dynamic-range (including nonlinear region) MW detection, making them particularly suitable for receiving frequency- and phase-modulated signals that are insensitive to power variations.
We show experimentally obtained frequency- and power-dependent optical response of a room-temperature cesium vapor cell used as a Rydberg microwave receiver based on electromagnetically induced transparency. An applied microwave field couples the 70S1/2{70S_{1/2}}70S1/2​ Rydberg state to the nearby 70P1/2{70P_{1/2}}70P1/2​, 70P3/2{70P_{3/2}}70P3/2​, 69P1/2{69P_{1/2}}69P1/2​, and 69P3/2{69P_{3/2}}69P3/2​ states, modifying the probe-transmission spectrum. Probe transmission is recorded over a 800 MHz range of coupling laser detunings. These EIT spectra are measured for RF frequencies from 9 to 13.5 GHz and over a 40 dB range of RF power. We analyze the RF induced splittings in the recorded EIT spectra. We observe both limiting cases, where the EIT peak separation is either dominated by the RF detuning or by the RF power. At higher powers we are also able to observe complex features due to coupling of multiple nearby Rydberg states. We further analyze the probe-transmission signal at zero coupling-laser detuning. Sigmoidal fits to the power-response curves are used to determine the midpoint power and the 10-90% transition interval as functions of RF frequency.
A long baseline phase-coherent microwave receiver is demonstrated using a remotely interrogated cesium Rydberg atom sensor over an 8 m free-space optical link. A 3.989 GHz local oscillator (LO) is intensity-modulated onto an 852 nm optical probe and recovered remotely for atomic superheterodyne detection. A 509 nm coupling laser establishes a Rydberg electromagnetically induced transparency (EIT) system addressing the 6S1/2 to 6P3/2 to 56D5/2 ladder, with microwave coupling to 57P3/2. A test signal offset by 5 kHz generates an optically detected intermediate-frequency (IF) response returned to the reference station for centralized coherent acquisition. This eliminates independent remote oscillators, electronic IF acquisition, and distributed clock synchronization. Over 10 min, the differential phase between remote and local reference exhibits a standard deviation of 0.476 deg and a minimum overlapping phase Allan deviation of 0.048 deg at approximately 200 s averaging. Following optical-link interruption, the differential phase recovers without recalibration, with a measured pre- and post-interruption difference of 0.01 deg. These results demonstrate phase coherent remotely interrogated atomic microwave reception with reduced instrumentation, supporting future distributed interferometry, multistatic radar, and coherent sensor arrays.
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.
We report the enhanced sensitivity of the Rydberg microwave (MW) receiver by exploiting the Doppler effect in a vapor cell. A two-photon Rydberg ladder scheme is implemented via the co-propagation of probe and coupling lasers, which enhances the Doppler effect. When an MW field is applied, microwave dressing modifies the velocity-dependent resonance condition, enabling stronger contributions from atoms with non-zero velocities and leading to an enhancement of the EIT transmission. Based on this mechanism, we achieve a sensitivity of 35.1 nV cm−1 Hz−1/235.1\ \mathrm{nV\ cm^{-1}\ Hz^{-1/2}}35.1 nV cm−1 Hz−1/2 using the heterodyne technique, which is 1.5 times better than that obtained in the counter-propagating configuration. Meanwhile, the required local oscillator (LO) field is reduced by a factor of 17.6 compared with the counter-propagating configuration, which is advantageous for applications requiring minimal radiation and low power consumption. Moreover, the co-propagating configuration is more amenable to integration or portable sensing platforms because multiple laser fields can be delivered through a single optical fiber.