In this paper, we propose a joint delay-Doppler estimation framework for Rydberg atomic quantum receivers (RAQRs) leveraging affine frequency division multiplexing (AFDM), as a future enabler of hyper integrated sensing and communication (ISAC) in 6G and beyond. The proposed approach preserves the extreme sensitivity of RAQRs, while offering a pioneering solution to the joint estimation of delay-Doppler parameters of mobile targets, which has yet to be addressed in the literature due to the inherent coupling of time-frequency parameters in the optical readout of RAQRs to the best of our knowledge. To overcome this unavoidable ambiguity, we propose a dual-chirp AFDM framework where the utilization of distinct chirp parameters effectively converts the otherwise ambiguous estimation problem into a full-rank system, enabling unique delay-Doppler parameter extraction from RAQRs. Numerical simulations verify that the proposed dual-chirp AFDM shows superior delay-Doppler estimation performance compared to the classical single-chirp AFDM over RAQRs.
In this paper, we propose a joint delay-Doppler estimation framework for Rydberg atomic quantum receivers (RAQRs) leveraging affine frequency division multiplexing (AFDM), as a future enabler of hyper integrated sensing and communication (ISAC) in 6G and beyond. The proposed approach preserves the extreme sensitivity of RAQRs, while offering a pioneering solution to the joint estimation of delay-Doppler parameters of mobile targets, which has yet to be addressed in the literature due to the inherent coupling of time-frequency parameters in the optical readout of RAQRs to the best of our knowledge. To overcome this unavoidable ambiguity, we propose a dual-chirp AFDM framework where the utilization of distinct chirp parameters effectively converts the otherwise ambiguous estimation problem into a full-rank system, enabling unique delay-Doppler parameter extraction from RAQRs. Numerical simulations verify that the proposed dual-chirp AFDM shows superior delay-Doppler estimation performance compared to the classical single-chirp AFDM over RAQRs.
We propose a multi-chirp affine frequency division multiplexing (MC-AFDM) scheme for joint delay-Doppler estimation with Rydberg atomic quantum receivers (RAQRs). The work is motivated by the fact that RAQRs, while offering superior sensitivity and advantageous sensing capabilities, suffer from an optical ambiguity due to Doppler shifts in doubly-dispersive (DD) channel caused by target mobility, which precludes the reliable estimation of delay-Doppler parameters. To resolve this optical ambiguity and unleash the potential of RAQRs in DD channel, the proposed MC-AFDM employs multiple distinct AFDM post-chirp signals to overcome the rank-deficiency problem of the classical single-chirp AFDM (SC-AFDM), thereby enabling accurate delay-Doppler estimation of multiple targets. Our analysis reveals that the edge distribution of the multiple post-chirp parameters can further improve estimation accuracy by minimizing the condition number. Building on the proposed MC-AFDM waveform, we design a sequential signal processing algorithm based on orthogonal matching pursuit (OMP) and least squares (LS), and we derive the theoretical lower bounds for delay and Doppler estimation. Numerical results show that the proposed MC-AFDM improves range and velocity estimation accuracy by up to two orders of magnitude compared to the classical SC-AFDM, and approaches its theoretical bounds through post-chirp optimization, validating the quantum-induced advantage of RAQRs for high-resolution quantum wireless sensing.
As a key enabler for next-generation wireless systems, integrated sensing and communication (ISAC) requires significantly higher receiver sensitivity than conventional architectures to achieve long-range target detection, thereby introducing new challenges in receiver design. Among potential solutions, Rydberg atomic quantum receivers (RAQRs) have attracted growing attention for their unique quantum sensing capabilities. By exploiting the exceptional responsiveness of Rydberg atoms to electromagnetic fields, RAQRs enable direct and highly sensitive measurement of radio-frequency (RF) signals without relying on traditional antenna-based front ends. However, this enhanced sensitivity also renders them more vulnerable to interference, particularly from undesired targets and long-delay multipath components. To address this limitation, this article presents practical strategies for improving the interference robustness and selective reception performance of RAQRs in ISAC scenarios. Specifically, we begin with a comprehensive overview of RAQR principles and identify the interference-related challenges encountered in ISAC applications. Building on this foundation, we introduce the Actively Selective RAQR (AS-RAQR) architecture, which integrates tunable gating mechanisms to actively suppress unwanted signals. The proposed design is validated through representative case studies, followed by a discussion of open challenges and future research directions.
Rydberg atomic quantum receivers (RAQR) exhibit exceptional sensitivity to radio-frequency (RF) signals, positioning them as promising candidates for next-generation wireless systems. Extending their capabilities to orthogonal frequency-division multiplexing (OFDM), however, requires atomic responses that go beyond broadband reception and are tailored to the structured interference of multicarrier signals. To bridge this gap, we develop an atomic-comb Rydberg receiver based on six-wave mixing (SWM) transduction. In particular, injecting a multi-tone local oscillator (LO) into the RAQR generates frequency-shifted replicas of the intrinsic SWM response. By subtly tuning the amplitude and phase of each LO tone, constructive and destructive interference can be selectively induced to preserve desired response components while attenuating harmful frequency offsets. Furthermore, we harness the response-reshaping capability of the proposed atomic comb to proactively mitigate OFDM interference. More explicitly, by exploiting the discrete difference-frequency structure of both carrier-frequency-offset (CFO)-induced and phase-noise (PN)-induced inter-carrier interference (ICI), we optimize the atomic-comb response to suppress dominant ICI components directly. We further reveal an intrinsic coupling between spectral shaping and the time-domain effective channel memory, motivating a joint optimization of both ICI and inter-symbol interference (ISI), which simultaneously suppresses inter-carrier leakage and post-cyclic-prefix (CP) tail energy. Extensive simulation results validate our atomic-comb design, unveiling that the proposed atomic comb can effectively reshape the receiver response over the OFDM, while mitigating ICI, shortening the effective channel memory, and substantially lowering CP overhead.
Rydberg-atom quantum receivers (RAQRs) offer highly sensitive RF reception, but their communication performance depends jointly on atomic response, optical transduction, receiver noise, bandwidth, and wireless-channel conditions. This paper develops a BER-aware communication-theoretic framework for superheterodyne RAQR-assisted wireless communication, linking four-level Rydberg-atom dynamics and coherent optical detection to multipath propagation and digital communication performance. Closed-form instantaneous and average SNR and BER expressions are derived for square Gray-coded M-QAM over correlated Rayleigh fading. The RAQR operating point is then jointly optimized over atomic, optical, RF, and geometric parameters using analytical block-wise updates within a fixed-point procedure subject to physical and bandwidth constraints. Numerical results demonstrate substantial gains in low-power reception, bandwidth utilization, robustness to detuning, fading and delay spread, outage, and communication coverage compared with conventional, advanced, and fixed-point RAQR receivers. The results demonstrate that BER-aware joint optimization translates the intrinsic sensitivity of Rydberg-atom sensing into tangible communication-level gains.
The significant progress of quantum sensing technologies offer numerous radical solutions for measuring a multitude of physical quantities at an unprecedented precision. Among them, Rydberg atomic quantum receivers (RAQRs) emerge as an eminent solution for detecting the electric field of radio frequency (RF) signals, exhibiting great potential in assisting classical wireless communications and sensing. So far, most experimental studies have aimed for the proof of physical concepts to reveal its promise, while the practical signal model of RAQR-aided wireless communications and sensing remained under-explored. Furthermore, the performance of RAQR-based wireless receivers and their advantages over classical RF receivers have not been fully characterized. To fill these gaps, we introduce the RAQR to the wireless community by presenting an end-to-end reception scheme. We then develop a corresponding equivalent baseband signal model relying on a realistic reception flow. Our scheme and model provide explicit design guidance to RAQR-aided wireless systems. We next study the performance of RAQR-aided wireless systems based on our model, and compare them to classical RF receivers. The results show that Doppler broadening-free RAQRs are capable of achieving a substantial received signal-to-noise ratio (SNR) gain of over 27 decibel (dB) and 40 dB in the photon shot limit and standard quantum limit regimes, respectively.
Quantum sensing technologies have experienced rapid progresses since entering the ‘second quantum revolution’. Among various candidates, schemes relying on Rydberg atoms exhibit compelling advantages for detecting radio frequency signals. Based on this, Rydberg atomic quantum receivers (RAQRs) have emerged as a promising solution to classical wireless communication and sensing. To harness the advantages and exploit the potential of RAQRs in wireless sensing, we investigate the realization of the direction of arrival (DOA) estimation by RAQRs. Specifically, we first conceive a Rydberg atomic quantum uniform linear array (RAQ-ULA) aided wireless receiver for multi-target DOA detection and propose the corresponding signal model of this sensing system. Our model reveals that the presence of the radio-frequency local oscillator in the RAQ-ULA creates sensor gain mismatches, which degrade the DOA estimation significantly by employing the classical Estimation of Signal Parameters via Rotational Invariant Techniques (ESPRIT). To solve this sensor gain mismatch problem, we propose the Rydberg atomic quantum ESPRIT (RAQ-ESPRIT) relying on our model. Lastly, we characterize our scheme through numerical simulations, where the results exhibit that it is capable of reducing the estimation error of its classical counterpart on the order of >400- fold and >9000- fold in the PSL and SQL, respectively.