基于里德堡原子的无线电光学测量及其光谱处理技术(特邀)

Rydberg atomic radio-optical measurement and spectrum processing techniques (invited)

  • 摘要: 里德堡原子是一种高激发态的原子,具有较大电偶极矩,相邻能级差可覆盖DC~THz的超宽频谱范围,因而可以实现电磁场高灵敏、超宽带的传感接收。基于里德堡原子的无线电光学测量是通过碱金属原子在探测光和控制光等两束激光的精确调控下转变为里德堡原子,并使探测光透射光谱产生电磁诱导透明效应,进而在输入的无线电信号的作用下,使其透明光谱发生Autler-Townes (AT)劈裂,完成无线电信号到光学信号的转化,从而实现无线电信号频率、幅度、相位等信息的提取,具有直接解调、无需校准、抗电磁毁伤等特点。近年来,该技术在电场计量、电磁频谱侦测、通信、雷达等电子信息技术领域引起人们的强烈关注。该技术的关键在于如何从原子系统输出光谱中快速准确地提取出无线电信号的信息。针对静态无线电信号、动态无线电信号、单频无线电信号、多频无线电信号等不同类型的无线电信号,对应的信息提取和光谱处理方式也不同。依据不同类型的无线电信号,对基于里德堡原子的无线电光学测量及其光谱处理技术进行分类,并综述其原理、技术特点及国内外研究进展,最后结合该技术特点及其应用前景,对未来发展趋势作了展望。

     

    Abstract:
      Significance   Rydberg atoms are highly excited atoms with large electric dipole moments. The energy difference between adjacent levels can cover an ultra-wide frequency spectrum range from DC to THz, making it possible to achieve high-sensitivity and ultra-wideband reception of electromagnetic fields. Radio-optical measurements based on Rydberg atoms are achieved by precisely controlling two laser beams, the probe laser and the control laser, to transform ground state alkali metal atoms into Rydberg atoms and induce Electromagnetic Induced Transparency (EIT) in the transmitted spectrum of the probe laser. Under the interaction of the input radio signal, Autler-Townes (AT) splitting occurs in the transparent EIT spectrum, completing the conversion of radio signals to optical signals (Fig.2-3), thereby extracting information such as frequency, amplitude, and phase of the radio signal. This technology has attracted great attention in electronic information fields such as electric field metrology, electromagnetic spectrum detection, communication, and radar in recent years. The physical implementation of this technology is simple and does not require strict physical conditions as usual quantum technologies such as single-photon sources or ultra-cold and superconducting conditions. It can be achieved at room temperature without being limited by the level of production technology. It is considered one of the fastest applicable quantum technologies with its high stability, accuracy, and repeatability that could partially replace existing radio reception technologies in the near future.
      Progress  In the past decade, researchers have made significant progress in the study of radio-optical measurement techniques based on Rydberg atoms, from precise measurements of single-frequency static radio signals in electric field metrology applications to real-time reception of single-frequency dynamic radio signals in communication applications, and to spectrum detection and communication reception of complex multi-frequency radio signals. The key to this technology is how to quickly and accurately extract information about the radio signal from the output EIT spectrum of the atomic system. Different types of radio signals, such as static, dynamic, single-frequency, and multi-frequency radio signals, require different information extraction and spectral processing methods, as well as different experimental designs and implementations. For single-frequency static radio signals, researchers have already used Rydberg atoms in experiments to measure field strengths in the 0-320 GHz frequency range with a maximum coverage range of 780 pV·cm−1 to 50 V·cm−1. By using heterodyne technology (Fig.8) and critical phenomena in many-body Rydberg atomic system, the current sensitivity can reach as low as 49 nV·cm−1·Hz−1/2. Unlike measuring single-frequency static radio signals, for single-frequency dynamic radio signals, Rydberg atom systems are required to track and respond to rapidly changing radio signals in real-time and quickly read EIT spectral changes at the end point. Its primary application scenario is the communication reception. Since 2018, a large number of verification experiments on wireless communication reception principle have been carried out based on Rydberg atoms. This technology can directly convert intermediate frequency or baseband signals on the carrier into optical signals for direct demodulation. Verified communication methods include amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). When the input wireless signal becomes complex, especially for multi-frequency wireless signal input, the output EIT spectrum of the probe laser will become complicated. It will be a big challenge to quickly and effectively read and distinguish information from different frequency wireless signals. Currently, a small amount of research is focused on verifying dynamic multi-frequency wireless signals for communication reception, including using multi-harmonic Rydberg atomic level structures to finely adjust and optimize system parameters at the front end or using post-processing techniques such as deep learning at the back end to achieve recognition and reading of multiple frequency information. People have experimentally achieved simultaneous reception of five completely different frequency signals within a spectrum range of over 100 GHz (Fig.18) or 20 similar frequency signals within a range of 100 kHz (Fig.23).
      Conclusions and Prospects  Through continuous research over the past 10 years, it has been experimentally verified that radio-optical measurements based on Rydberg atoms have unique quantum advantages in spectrum range, sensitivity, minimum field strength, signal demodulation mechanism, and other aspects. This technology has demonstrated promising prospects in applications such as electric field metrology, electromagnetic spectrum detection, communication, radar, and more. In order to further develop this technology to fully leverage the unique quantum advantages of Rydberg atoms and achieve practical applications as soon as possible, researchers need to deepen their research on the comprehensive performance improvement, anti-interference ability enhancement, miniaturization integration and simultaneously reduce the costs of radio-optical measurements based on Rydberg atoms.

     

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