Superdirective receive arrays, whose gain can exceed that of traditional antenna arrays, have been historically challenging to realize due to high sensitivity to white noise, strong mutual coupling, and the complexity of designing receive matching networks in conventional systems. This paper proposes and analyzes a novel superdirective receiver architecture based on an array of Rydberg atomic sensors to overcome these fundamental limitations. By leveraging the quantum properties of Rydberg atoms, the proposed receiver is inherently immune to the internal thermal noise that plagues traditional receivers. As a result, the system performance is primarily limited by external background noise and fundamental quantum noise. We develop a comprehensive signal and noise model and the-oretically derive the upper bound on the directivity gain for the proposed Rydberg-based receiver. Furthermore, we prove that for multi-user scenarios, the effective channel vectors for different users become asymptotically orthogonal as the number of sensors approaches infinity, enabling high-capacity spatial multiplexing even with deep sub-wavelength element spacing. Extensive simulations demonstrate the superior performance of the proposed system over traditional superdirective receivers and validate our theoretical findings. The results highlight Rydberg atomic arrays as a promising technology for developing ultra-sensitive, compact, and broadband superdirective receivers for next-generation communication and sensing applications.
Superdirective receive arrays, whose gain can exceed that of traditional antenna arrays, have been historically challenging to realize due to high sensitivity to white noise, strong mutual coupling, and the complexity of designing receive matching networks in conventional systems. This paper proposes and analyzes a novel superdirective receiver architecture based on an array of Rydberg atomic sensors to overcome these fundamental limitations. By leveraging the quantum properties of Rydberg atoms, the proposed receiver is inherently immune to the internal thermal noise that plagues traditional receivers. As a result, the system performance is primarily limited by external background noise and fundamental quantum noise. We develop a comprehensive signal and noise model and the-oretically derive the upper bound on the directivity gain for the proposed Rydberg-based receiver. Furthermore, we prove that for multi-user scenarios, the effective channel vectors for different users become asymptotically orthogonal as the number of sensors approaches infinity, enabling high-capacity spatial multiplexing even with deep sub-wavelength element spacing. Extensive simulations demonstrate the superior performance of the proposed system over traditional superdirective receivers and validate our theoretical findings. The results highlight Rydberg atomic arrays as a promising technology for developing ultra-sensitive, compact, and broadband superdirective receivers for next-generation communication and sensing applications.
Rydberg atomic quantum receivers have been seen as novel radio frequency measurements and the high sensitivity to a large range of frequencies makes it attractive for communications reception. However, current implementations of Rydberg array antennas predominantly rely on simple stacking of multiple single-antenna units. While conceptually straightforward, this approach leads to substantial system bulkiness due to the unique requirements of atomic sensors, particularly the need for multiple spatially separated laser setups, rendering such designs both impractical for real-world applications and challenging to fabricate. This limitation underscores the critical need for developing multiplexed Rydberg sensor array architectures. In the domain of conventional RF array antennas, hybrid analog-digital beamforming has emerged as a pivotal architecture for large-scale millimeter-wave (mmWave) multiple-input multiple-output (MIMO) systems, as it substantially reduces the hardware complexity associated with fully-digital beamforming while closely approaching its performance. Drawing inspiration from this methodology, we conduct a systematic study in this work on the design principles, equivalent modeling, and precoding strategies for low-complexity multiplexed Rydberg array, an endeavor crucial to enabling practical and scalable quantum-enhanced communication systems.
In recent years, electric field measurement techniques based on Rydberg atoms have shown unique advantages in high sensitivity and wideband applications and miniaturization. The Rydberg atom receiver senses the electromagnetic signal using the quantum coherence effect, which overcomes the inherent defects of traditional electronic receivers in terms of thermal noise, insertion loss of microwave devices, and the use of wavelength-dependent antennas, thus providing the Rydberg atomic receivers the potential to become the next generation of microwave receivers. For some particular application scenarios such as radar and communication, superheterodyne reception is a critical technical approach, and the linear dynamic range is an essential factor in evaluating the performance of the superheterodyne receivers. It is challenging to promote the Rydberg atomic receiver without figuring out the influence of system parameters on the linear dynamic range. This paper starts with the response mechanism of the Rydberg atomic superheterodyne receiver, and a theoretical model is established to simulate the atom-microwave responses. Then the harmonics' generation mechanism is discussed, and the atomic linear dynamic range under different probe light Rabi frequencies is studied further. Furthermore, a method to evaluate the antiblocking performance of the system is proposed. This work is expected to provide theoretical guidance for the design and performance optimization of the Rydberg atomic superheterodyne receiver.
Rydberg atoms are atoms in their highly excited energy states. The physical properties of Rydberg atoms in the presence of external fields play an important role in quantum precision measurement. In recent years, radio-frequency electric field sensing based on Rydberg atoms has attracted significant interest. It is widely recognized as an electromagnetic sensing system fundamentally different from traditional ones. As a quantum sensor, it is expected to surpass several foundational limitations of traditional receivers, such as sensitivity, dynamic range and frequency bandwidth. It was reported that Rydberg sensing systems can sense microwaves of frequencies from DC up to 1THz. Its quantum nature would possibly avoid internal thermal (Johnson) noise, even at room temperature. Recent demonstrations have also observed high precision for terahertz imaging, strong fields sensing, proof-of-principle communication. However, limitations of this novel system have not been addressed, especially for a practical radar, communication or electronic warfare system. Here in this work, we first compare the architectures of different microwave receivers and then analyze the metrics of Rydberg microwave receivers, such as instantaneous bandwidth and dynamic range based on experimental results. We concluded by pointing out several main obstacles to overcome for realizing a practical state-of-the-art microwave receiver.
With the escalating development of the quantum information technologies, the Rydberg atomic receiver has been envisioned as a promising alternative to its classical electronic counterparts, attracting extensive attentions from both physics and electronic engineering disciplines. By exploiting the electrical acuteness of Alkali atoms with diverse Rydberg energy states for electromagnetic field measurement, Rydberg atomic receiver is capable of surmounting the inherent limitations on the operating bandwidth and detection sensitivity of the classical electronic counterparts. Against this background, this article provides an extensive overview of Rydberg atomic communication and sensing from fundamental theory, critical technologies to practical implementations. Firstly, the milestones of the Rydberg atomic receiver evolution was introduced. Then we provide a clear understanding of Rydberg atomic receiver mechanisms from the perspective of classical communication and sensing, and highlight the unprecedented advantages over traditional electronic receivers as well as the technical challenges. Afterwards, necessary fundamentals are presented including the Rydberg atoms, typical non-coherent/coherent structures, and explicit experimental configurations, followed by discussions on state-of-the-art development of the Rydberg atomic receiver. Specifically, advancements on electric-field detection methods for accurate measurement of amplitude, phase, frequency and polarization, are extensively investigated. Based on the established methodologies, recent innovations in Rydberg atomic communication and sensing are reviewed, ranging from waveform design and array-based signal processing to radar applications like localization, imaging and remote sensing, with practical experimental results presented. Finally, we summarize the promising research trends around Rydberg atomic receiver.
Rydberg atom-based antennas exploit the quantum properties of highly excited Rydberg atoms, providing unique advantages over classical antennas, such as high sensitivity, broad frequency range, and low intrinsic noise. Despite the increasing interests in their applications in antenna and communication engineering, some key properties, involving the lack of polarization multiplexing and isotropic reception without mutual coupling, remain unexplored in the analysis of Rydberg atom-based multiple-input–multiple-output (MIMO) communications. Generally, the design considerations for any antenna, even for atomic ones, can be extracted to factors, such as radiation pattern, efficiency, and polarization, allowing them to be seamlessly integrated into existing system models. In this letter, we extract the antenna properties from relevant quantum characteristics, enabling electromagnetic modeling and capacity analysis of Rydberg MIMO systems in both far-field and near-field scenarios. Focusing on spatial multiplexing performance under the same signal-to-noise level, our results indicate that Rydberg atom-based antenna arrays offer certain advantages over classical dipole-type arrays in single-polarization MIMO communications.
The rapid development of the quantum technology presents huge opportunities for 6G communications. Leveraging the quantum properties of highly excited Rydberg atoms, Rydberg atom-based antennas present distinct advantages, such as high sensitivity, broad frequency range, and compact size, over traditional antennas. To realize efficient precoding, accurate channel state information is essential. However, due to the distinct characteristics of atomic receivers, traditional channel estimation algorithms developed for conventional receivers are no longer applicable. To this end, we propose a novel channel estimation algorithm based on projection gradient descent (PGD), which is applicable to both one-dimensional (1D) and two-dimensional (2D) arrays. Simulation results are provided to show the effectiveness of our proposed channel estimation method.