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arXiv:2503.22864 · AIP Advances

Microwave phase mapping and angle-of-arrival detection using Rydberg atom-based electrometry

Alexander Gill, A. Buikema, S. Sirisky, Hannah Clevenson

Published Feb 1, 2026• 0 citations
arXivHTMLPDF

Abstract

We present a method for simultaneously measuring the phase fronts of three or more RF fields using thermal Rydberg atoms. We demonstrate this method using an all-dielectric atomic electrometer acting in a heterodyne configuration to detect three single tone continuous-wave microwave signals propagating in free space. We show that this method can be used to measure the angle of arrival of each source. This method requires no calibration of the incident fields and assumes only far-field distance and phase stability of the incident phase fronts. Because the sensor is minimally perturbing, it provides a direct probe of signal phase even in complex environments, such as the near field of an antenna source or a scattering surface. The measurements presented here are performed using a single scanned sensor, but this technique can trivially be extended to an array of sensors, which would enable phase-sensitive imaging and related applications.

DOI
10.1063/5.0278352

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We present a method for simultaneously measuring the phase fronts of three or more RF fields using thermal Rydberg atoms. We demonstrate this method using an all-dielectric atomic electrometer acting in a heterodyne configuration to detect three single tone continuous-wave microwave signals propagating in free space. We show that this method can be used to measure the angle of arrival of each source. This method requires no calibration of the incident fields and assumes only far-field distance and phase stability of the incident phase fronts. Because the sensor is minimally perturbing, it provides a direct probe of signal phase even in complex environments, such as the near field of an antenna source or a scattering surface. The measurements presented here are performed using a single scanned sensor, but this technique can trivially be extended to an array of sensors, which would enable phase-sensitive imaging and related applications.
In this work, we demonstrate the use of a Rydberg atom-based sensor for determining the angle of arrival of an incident radio frequency (RF) wave or signal. The technique uses electromagnetically induced transparency in Rydberg atomic vapor in conjunction with a heterodyne Rydberg atom-based mixer. The Rydberg atom mixer measures the phase of the incident RF wave at two different locations inside an atomic vapor cell. The phase difference at these two locations is related to the direction of arrival of the incident RF wave. To demonstrate this approach, we measure phase differences of an incident 19.18 GHz wave at two locations inside a vapor cell filled with cesium atoms for various incident angles. Comparisons of these measurements with both the full-wave simulation and the plane wave theoretical model show that these atom-based sub-wavelength phase measurements can be used to determine the angle of arrival of an RF field.
Deep subwavelength radio-frequency (RF) imaging with atomic Rydberg sensors has overcome fundamental limitations of traditional antennas and enabled ultra-wideband detection of omni-directional time varying fields all in a compact form factor. However, in most applications, Rydberg sensors require the use of a secondary strong RF reference field to serve as a phase reference. Here, we demonstrate a new type of Rydberg sensor for angle-of-arrival (AoA) sensing, which utilizes subwavelength imaging of standing wave fields. By placing a metallic plate within the Rydberg cell, we can determine the AoA independent of the strength of incoming RF field and without requiring a secondary strong RF phase reference field. We perform precision AoA measurements with a robotic antenna positioning system for 4.2, 5.0, and 5.7 GHz signals and demonstrate a 1.7° polar angular resolution from 0° to 60° AoA and 4.1° over all possible angles.
The electric field sensing technology based on the Rydberg atom has attracted widespread attention due to its powerful detection ability for the amplitude, phase, and polarization of the electric field. In this work, based on the electromagnetically induced transparency (EIT) of the Rydberg atom and combined with a heterodyne Rydberg atom-based mixer, we measured the binary array composed of the Rydberg Field Probes (RFPs). The measured phase difference of the electric field at two different RFPs is related to the direction of incidence. We digitally transform the received signal at 2.63 GHz and conduct digital beamforming (DBF) processing to obtain its array pattern and beam direction. The measurement accuracy and reliability are greatly improved compared with the phase comparison method, and the angle-of-arrival (AOA) variance is less than 1.5°. The effectiveness of DBF based on the Rydberg atomic sensor is verified, which lays the foundation for the subsequent linear and planar array reception of the Rydberg atomic sensor. In addition, the occlusion based on RFPs is also measured, and its weak occlusion characteristics are confirmed. This unique feature provides feasible support for the 3-D receiving array based on the Rydberg atomic sensor.
The determination of the angle of arrival (AoA) of Ku-band microwave signals is of great significance in satellite communications, spectrum monitoring, and national defense security, which has created an urgent demand for high-precision and interference-resistant passive detection techniques. In this study, we propose a Rydberg-atom-based passive measurement method for estimating the AoA of Ku-band incident signals. Based on well-established quantum optical techniques, the proposed method converts the EIT-AT splitting intervals induced by waves or signals incident from different directions in Rydberg atoms within a single vapor cell into the electric-field intensity at the atomic sensor. An electric-field-intensity-angle response model is then established for AoA estimation of a 13.6 GHz wave or signal. Simulation results demonstrate that the proposed method can determine the incident direction within a certain angular range, with an estimation error of less than 3.8°. Without the need for self-calibration and free from interference caused by actively emitted probing electromagnetic waves or reference electric fields, the proposed approach enables AoA determination of incident waves or signals using a single vapor cell with a length of 5 cm.
Radio-frequency (rf) receivers using Rydberg atoms offer appealing features over classical sensors, such as their size, frequency tuning range, and lack of field absorption. In this work, we extend the application space by demonstrating a Rydberg atom rf polarimeter. Using rf heterodyne with three independent and orthogonal local oscillators, we are able to extract the polarization ellipse of the field in three dimensions, in addition to the total amplitude of the field. We use the relative phases and amplitudes of the three generated heterodyne signals to measure the field amplitudes and phases along three cardinal axes giving the full three-dimensional polarization. We demonstrate this polarization measurement for incoming fields at different angles around the sensor. Lastly, we investigate the reception of data symbols encoded in the horizontal and vertical signal field polarizations and the phase between them. Our measurements yield an amplitude noise of $57\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{V}/\mathrm{m}/\sqrt{\text{Hz}}$ for horizontal polarization, $66\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{V}/\mathrm{m}/\sqrt{\text{Hz}}$ for vertical polarization, and a standard deviation of 0.094 rad in the phase between the field components.
We present on the recent development of an atomic antenna probe and front-end based on Rydberg atoms for applications in radio-frequency (RF) imaging and synthetic apertures. Fundamental atom-RF responses and RF amplitude and phase determination methods for Rydberg atom probes are described. We demonstrate electric field imaging in the near-field of a 2.5 GHz Yagi-Uda antenna device under test (DUT) using a portable Rydberg atom probe and integrated front-end, the Rydberg Field Probe (RFP). A wide-area RF electric field map is generated by positioning of the RFP at discrete spatial measurement locations in the near field of the DUT, from which a composite image of the two-dimensional antenna pattern is realized at a spatial resolution of λ/2\lambda /2λ/2 and field uncertainties within 5.5%. Finally, we demonstrate RF phase imaging of a 100 GHz field using a Rydberg EIT optical fluorescence imager and RF self-homodyning, towards RF phase-sensing and imaging at millimeter-wave frequencies.