arXiv:2601.20062

Comment on "Determining angle of arrival of radio-frequency fields using subwavelength, amplitude-only measurements of standing waves in a Rydberg atom sensor"

M. Chilcott, N. Kjærgaard

quant-phphysics.atom-phSubmitted Jan 27, 2026• Announced Jan 29, 2026

Abstract

We discuss the consequence of excluding allowed RF-transition between substates of a field-dressed Rydberg manifold when predicting the spectrum that will be observed if the dressed system is probed in an optical EIT scheme.

Journal reference: Journal of Applied Physics 139, 226101 (2026)
DOI: 10.1063/5.0310791
Comments: Comment on arXiv:2502.09835 published in J. Appl. Phys. 138, 114402 (2025). The following article has been submitted to Journal of Applied Physics

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arXiv:2601.20062

Comment on "Determining angle of arrival of radio-frequency fields using subwavelength, amplitude-only measurements of standing waves in a Rydberg atom sensor"

M. Chilcott, N. Kjærgaard

quant-phphysics.atom-phSubmitted Jan 27, 2026• Announced Jan 29, 2026

arXiv HTML PDF

Abstract

Journal reference: Journal of Applied Physics 139, 226101 (2026)
DOI: 10.1063/5.0310791
Comments: Comment on arXiv:2502.09835 published in J. Appl. Phys. 138, 114402 (2025). The following article has been submitted to Journal of Applied Physics

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Rydberg atoms in a vapor cell are used to measure the angle-of-arrival (AoA) of an incident radio-frequency plane wave through sub-wavelength phase measurements using a heterodyne technique.

Conference on Lasers and Electro-OpticsJan 1, 20213 citations

Determining angle of arrival of radio-frequency fields using subwavelength, amplitude-only measurements of standing waves in a Rydberg atom sensor

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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.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.

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|m_J|

sublevels, while their relative excitation strengths depend strongly on the relative orientation of the RF and optical polarizations. Under the controlled polarization geometry considered here, this dependence enables determination of the AoA magnitude without requiring RF phase measurements or spatially separated sensing locations. We experimentally demonstrate the method at RF frequencies of 1.27 GHz, 2 GHz, 3 GHz, and 4 GHz using a subwavelength cesium vapor cell. Within the

20^\circ-40^\circ

region of highest angular sensitivity, the estimated repeatability-based

1σ

AoA uncertainty ranges from approximately

0.6^\circ

2^\circ

across the investigated RF frequencies. A model combining Floquet-Shirley calculations of the RF-dressed Rydberg states with a coherent hyperfine-to-fine-structure optical excitation model qualitatively reproduces the experimental observations. These results establish a path toward compact, phase-independent AoA sensing using spatially localized Rydberg-atom spectroscopy.