Rydberg Array Reuse Enables Low-Complexity Receiver Design for Sparse Channels and Novel Radio Frequency Measurements

Rydberg atomic receivers represent a promising new approach to radio frequency technology, offering exceptional sensitivity across a broad spectrum of frequencies and attracting considerable interest for future communication systems. Hao Wu, Shanchi Wu, and Xinyuan Yao from the University of Science and Technology of China, along with Rui Ni and Chen Gong, now demonstrate a significant advance in this field by tackling the challenge of scaling up Rydberg array antennas. Current designs suffer from excessive bulkiness due to the complex laser systems required for each antenna element, hindering practical implementation. This research introduces a novel multiplexed Rydberg array architecture, inspired by techniques used in conventional radio frequency systems, that dramatically reduces hardware complexity while maintaining high performance, paving the way for scalable and efficient communication networks.

Straightforward approaches to building atomic sensors often result in bulky systems, particularly due to the need for individual laser setups for each sensing element. This limits their practicality and complicates fabrication. Consequently, researchers are focusing on developing multiplexed Rydberg sensor array architectures to overcome these challenges. In the field of radio frequency communication, hybrid analog-digital beamforming has proven effective in large-scale millimeter-wave systems by reducing hardware complexity compared to fully-digital approaches.

Rydberg Atoms Detect Millimeter Wave Signals

This research explores the use of Rydberg atoms as highly sensitive sensors for detecting radio frequency signals, with a particular focus on millimeter wave communication. Rydberg atoms excel in this role due to their strong interaction with electric fields and the principle of electromagnetically induced transparency, which allows for sensitive detection. Researchers are investigating hybrid beamforming and precoding techniques, methods for combining analog and digital signal processing to create focused beams and overcome signal loss. Accurate channel estimation, determining the characteristics of the communication channel, is also crucial for reliable communication, as is direction of arrival estimation, identifying the source of a signal to improve beam steering and reduce interference.

Improving the design of the vapor cell, the container holding the Rydberg atoms, is a key area of focus, including optimizing its geometry and incorporating resonant structures like split-ring resonators to enhance signal interaction and maximize the atoms’ sensitivity. Researchers acknowledge that non-uniform electric fields can distort sensor readings and are developing methods to address these distortions. Optimizing vapor cell design and applying Rydberg atom sensing to millimeter wave networks are central themes. Researchers are also exploring spatial multiplexing, using multiple antennas to increase data rates, and developing methods to mitigate interference.

The use of low-resolution phase shifters in hybrid beamforming and the application of lattice-based beamforming are also being investigated, alongside the potential of nonlinear Rydberg atomic sensors. Based on this research, future work could focus on advanced vapor cell designs to enhance signal interaction, minimize noise, and improve stability. Developing robust channel estimation algorithms that are resilient to noise and interference is also crucial. Adaptive beamforming techniques that dynamically adjust beam direction to track moving users and mitigate interference are essential for high-performance systems.

Integrating machine learning techniques to improve all aspects of Rydberg atom-based sensing and communication, including channel estimation, beamforming, and signal processing, holds significant promise. Miniaturizing and integrating Rydberg atom-based sensors and communication systems for real-world deployment is another key goal. Exploring the use of these sensors in other frequency bands, such as terahertz, where high bandwidth is available, is also being considered. Addressing the effects of non-uniform electric fields on sensor accuracy and improving the energy efficiency of these systems are important challenges. Combining data from multiple Rydberg atom sensors to improve accuracy and reliability, and exploring security applications for secure communication and authentication, are also areas of interest. This research represents a rapidly evolving field with the potential to revolutionize wireless communication and sensing, drawing on expertise in atomic physics, electromagnetics, signal processing, and machine learning.

Scalable Rydberg Receiver with Beamforming Architecture

Researchers have developed a new multiplexed Rydberg array architecture to overcome limitations in current receiver systems, specifically the bulkiness caused by individual laser setups. Inspired by hybrid analog-digital beamforming techniques used in millimeter-wave communication, this design significantly reduces hardware complexity and enables scalable communication systems. The core of this advancement lies in a method that decomposes complex signal processing operations into smaller, independent subproblems, eliminating the need for iterative computation. Experiments demonstrate the creation of a receiver with 36 antenna elements, expandable to 216 through the implementation of cell and local oscillator blocks, resulting in substantial improvements in spectral efficiency.

Data shows that increasing the number of local oscillator reuse blocks, while maintaining a constant number of laser chains, directly enhances system performance. Specifically, the team measured spectral efficiency gains as the number of antenna elements increased, preserving these gains even with limited resolution local oscillator phase shifts. Further analysis reveals that the proposed architecture achieves optimal performance with a specific configuration where the local oscillator reuse depth is divisible by the analog-to-digital converter reuse depth. Under these conditions, the team recorded performance equivalent to continuous-phase scenarios, demonstrating the effectiveness of the precoding algorithm and reuse design. Measurements confirm that the system achieves higher spectral efficiency with fewer analog-to-digital converters, compared to conventional antenna designs, validating the benefits of both local oscillator and analog-to-digital converter reuse.

Rydberg Arrays Outperform Traditional Antenna Designs

This work establishes a theoretical framework for designing multiplexed antenna arrays using Rydberg atom sensors for massive multiple-input multiple-output communication systems. Researchers introduced two novel reuse strategies, encompassing both local oscillator and analog-to-digital converter sharing configurations, to reduce hardware complexity. A hybrid precoding algorithm, employing an alternating optimization approach, was developed and numerically validated, demonstrating significant performance advantages over conventional antenna arrays. Specifically, simulations reveal that the proposed Rydberg reuse array outperforms traditional uniform planar arrays under comparable conditions, though it is surpassed by non-uniform planar arrays with optimized phase center mapping.

This performance hierarchy arises from the inherent frequency reuse strategy of the Rydberg array design. The team acknowledges that performance is impacted by the finite resolution of phase control, a limitation inherent in practical implementations. Future work could focus on mitigating these resolution effects and exploring the potential of these multiplexed arrays in more complex communication scenarios. These findings represent a substantial advance in Rydberg atom-based communication, paving the way for more scalable and efficient wireless systems.