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IEEE Microwave and Wireless Technology Letters

Quadrupole Interaction-Based Detection of OAM Microwaves Using Rydberg Atoms

Zheyuan Wang, Chao Zhang

Published Oct 30, 2025• 0 citations
Publisher

Abstract

The orbital angular momentum (OAM) technology, promising for future communications, radar, and quantum information processing, confronts challenges in OAM detection of the microwave photons, due to the noise and equipment complexity. Conventional detection approaches based on gyrotron systems, which demand vacuum and high-voltage environments, prove impractical for scalable applications. Thus, we introduce a Rydberg-atom-based architecture for OAM detection of vortex microwave photons, which operates in normal pressure and low voltage with miniaturized equipment. Specifically, leveraging the unique dipole-forbidden, quadrupole-allowed transitions of Rydberg atoms, we can receive the vortex microwave photons and identify the corresponding intrinsic OAM (IOAM), with precise frequency alignment by external electrode plates for fine-tuning. Moreover, experimental observations reveal the insight of Autler–Townes splitting, confirming that the OAM of microwave photons can couple to atomic energy levels through electric-quadrupole interactions, inducing a dynamic Stark effect. In contrast, the experiments with plane microwave photons, i.e., the OAM mode is zero, show the result with only static stark broadening rather than the peak splitting, which highlights the critical role of quadrupole transitions in OAM detection. Significantly, this approach overcomes the limitations of conventional techniques requiring high-energy superconducting devices or high-voltage setups, offering a low-cost, scalable solution for efficient vortex microwave photons detection with promising applications, e.g., secure wireless communications and quantum radars.

DOI
10.1109/lmwt.2025.3621009

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The orbital angular momentum (OAM) technology, promising for future communications, radar, and quantum information processing, confronts challenges in OAM detection of the microwave photons, due to the noise and equipment complexity. Conventional detection approaches based on gyrotron systems, which demand vacuum and high-voltage environments, prove impractical for scalable applications. Thus, we introduce a Rydberg-atom-based architecture for OAM detection of vortex microwave photons, which operates in normal pressure and low voltage with miniaturized equipment. Specifically, leveraging the unique dipole-forbidden, quadrupole-allowed transitions of Rydberg atoms, we can receive the vortex microwave photons and identify the corresponding intrinsic OAM (IOAM), with precise frequency alignment by external electrode plates for fine-tuning. Moreover, experimental observations reveal the insight of Autler–Townes splitting, confirming that the OAM of microwave photons can couple to atomic energy levels through electric-quadrupole interactions, inducing a dynamic Stark effect. In contrast, the experiments with plane microwave photons, i.e., the OAM mode is zero, show the result with only static stark broadening rather than the peak splitting, which highlights the critical role of quadrupole transitions in OAM detection. Significantly, this approach overcomes the limitations of conventional techniques requiring high-energy superconducting devices or high-voltage setups, offering a low-cost, scalable solution for efficient vortex microwave photons detection with promising applications, e.g., secure wireless communications and quantum radars.
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Quantum Orbital Angular Momentum (OAM) indicates that each Electro-Magnetic (EM) photon of an EM wave carries OAM. In the microwave band, such an EM wave photon is called a vortex microwave photon. Physical properties distinguish between EM waves with vortex and plane wave photons. When illuminating a traditional stealthy target composed of absorbing materials, a vortex microwave photon can achieve higher echo power, thereby improving the Radar Cross Section (RCS), the corresponding receiving signal power, and detection probability. Hence, the vortex microwave photon shows promise in antistealth technology. In this paper, a vortex microwave quantum radar based on the OAM quantum state is proposed. Its basic physical architecture and corresponding mathematical model are given, and the high echo power characteristics of the vortex microwave photon are analyzed using Quantum Electro-Dynamics (QED). The correctness of the theoretical calculation was experimentally verified with an approximate 9 dB improvement in echo power. Moreover, the simulations are performed to clarify the improvement in radar performance, including the receiving power and detection probability, illustrating the capability of the vortex microwave photon when applied to antistealth radar.
Optical vortex beams (OVBs) carrying orbital angular momentum (OAM) offer access to an unbounded set of orthogonal states, enabling a dramatic increase in the information capacity for optical communication systems. However, practical OAM detection in telecommunication platforms remains challenging due to background noise, detector limitations at infrared communication wavelengths, and the destructive nature of conventional sampling methods. Here, we introduce an all-optical, nearly nondestructive OAM detection method based on sum-frequency generation (SFG) that overcomes these limitations by transferring the information on the OAM into a distinct frequency domain. In our scheme, two OVBs─one carrying OAM-encoded information and the other serving as a reference─are coupled within a beta-barium borate (BBO) crystal to generate an SFG signal. Our theoretical and experimental studies demonstrate that SFG efficiency is governed by the spatial overlap of the interacting vortex profiles, providing mode-selective and OAM-resolved detection. Crucially, as only a small fraction of the input photons undergo conversion into the nonlinear signal, the original beams remain functionally intact. Since detection is performed exclusively on the upconverted signal in a spectrally distinct visible wavelength region, the signal-to-noise ratio can be improved. Moreover, the SFG signal is generated only when specific OAM states and temporal overlap conditions are simultaneously satisfied, enabling ultrafast and conditionally gated access to the OAM information. This nonlinear selectivity offers enhanced physical-layer security and high-throughput capabilities. Together, our approach provides a robust and versatile platform for advanced OAM-based optical communications and high-capacity photonics applications.
The OAM quantum properties of photons, especially microwave photons, have been extremely attractive for researches. However, the research on the quantum properties of microwave photons has been limited due to the use of superconducting or cryogenic environments. To address this problem, the use of Rydberg Atoms, which can operate at room temperature and pressure, has been proposed as our solution in this paper. Furthermore, we propose an OAM keying encoding method for microwave quantum with the utilization of Rydberg atom detection. The proposed system exhibits excellent noise immunity, which is a crucial factor in maintaining reliable performance. The potential consequence of this advancement is the ability to minimize the size of the quantum characterization device for microwave photons, which may enable it to fit within a compact box.
Communication technologies advance toward secure communication, with frequency hopping communication (FH-C) widely used. However, traditional FH-C is limited by slow hopping speed, narrow bandwidth, and a few hopping points. Rydberg atoms offer a solution but face challenges like poor non-resonant microwave sensitivity and local oscillator synchronization limits. Here, we propose a frequency-hopping receiver based on atomic heterodyne detection that employs high orbital angular momentum (high-OAM) Rydberg states for resonant detection of rapidly hopping radio-frequency signals across multiple, widely separated frequency bands. The high-OAM Rydberg atoms ( l =3,4,5) resonantly detect 315 MHz, 1.7 GHz, and 29.74 GHz RF hopping signals (spanning 6 octaves). With heterodyne detection and a continuous excitation scheme, the system eliminates spectral establishment time, achieving 60 khops/s without transmitter-receiver synchronization, and uses frequency combs to extend hopping points to 5 MHz around resonant frequencies. These advances demonstrate the potential of Rydberg-atom–based receivers for high-speed and wide-band frequency-hopping communication.
Recent advances in Rydberg-atom electrometry detail promising applications in radio frequency communications. Presently, most applications use carrier frequencies greater than 1 GHz where resonant Autler–Townes splitting provides the highest sensitivity. This letter documents a series of experiments with Rydberg atomic sensors to collect and process waveforms from the automated identification system (AIS) used in maritime navigation in the very high frequency (VHF) band. Detection in this band is difficult with conventional resonant Autler–Townes based Rydberg sensing and requires a new approach. We show the results of a method called high angular momentum matching excited Raman (HAMMER), which enhances low frequency detection and exhibits superior sensitivity compared to the traditional AC Stark effect. From measurements of electromagnetically induced transparency in rubidium and cesium vapor cells, we show the relationship between incident electric field strength and observed signal-to-noise ratio and find that the sensitivity of the HAMMER scheme in rubidium achieved an equivalent single VHF tone sensitivity of 100μV/m/Hz. With these results, we estimate the usable range of the atomic vapor cell antenna for AIS waveforms given current technology and detection techniques.