涡旋电磁波轨道角动量传输的量子电动力学分析

Quantum electro-dynamics analysis of vortex electro-magnetic wave transmission with orbital angular momentum

随着可用频率等无线传输资源逐渐消耗殆尽,基于电磁波轨道角动量(orbital angular momentum,OAM)新维度的数据传输成为未来无线通信系统潜在核心关键技术.具有OAM的电磁波被称为涡旋电磁波,具体可分为通过回旋电子辐射生成的涡旋电磁波量子,以及由不同相位的电磁波量子叠加生成的统计态涡旋波束.然而,由于统计态涡旋波束被认为是基于多天线的多输入多输出(multipleinput multiple-output,MIMO)系统的一种在直射信道环境下波束成形的特例,从而对电磁波OAM传输是否具有新维度产生争论.特别是从微观层面到宏观层面,目前缺少相应理论文献和分析方法予以澄清.为解决这个问题,本文提出了一种基于量子电动力学(quantum electro-dynamics,QED)的轨道角动量分析方法,结合统计物理学概念,对涡旋电磁波轨道角动量传输过程进行分析,明确了量子态和统计态的区别.本文的主要创新点包括:(1)提出了一种结合统计物理学的量子电动力学分析方法,建立了电磁波微观状态与宏观状态的桥梁;(2)采用所提方法,对统计态OAM涡旋波束进行了全面分析,并与量子态OAM涡旋电磁波量子进行了充分对比;(3)针对涡旋电磁波物理新维度的质疑,明确了量子态OAM为无线传输系统提供新维度.本文分析指出:量子态OAM涡旋电磁波量子与统计态OAM涡旋波束关于轨道角动量定义的内涵是不同的,分别属于内禀和外部OAM,从而导致了统计态OAM涡旋波束的外部OAM与电场强度的空域紧耦合,这也是统计态OAM涡旋波束传输不会超过传统多天线MIMO传输最大容量界的根本原因;与之相比,量子态OAM则是在物理上完全独立于电场强度且与宏观空域解耦,可构成无线传输新维度.因此,含有内禀OAM的量子态OAM涡旋电磁波量子是开发电磁波新资源的发展方向,以其为核心关键技术的无线通信系统则是未来的发展趋势.

With the gradual exhaustion of wireless transmission resources such as the frequency,transmission schemes based on the orbital angular momentum(OAM)of electromagnetic(EM)waves have become the potential key technology of next-generation wireless communications.An EM wave with OAM is usually called a vortex EM wave,which can be classified into two types,the quantum vortex photons generated by the cyclotron radiation and the vortex beams with OAM statistically generated by the superposition of different plane EM waves.However,because the statistical OAM vortex beams are considered as the special case of multiple-input multiple-output(MIMO)systems in the line-of-sight(LoS)channel environment,it is debated whether the EM wave transmission with OAM is a new dimension in wireless transmissions and communications.In particular,from the microscopic to the macroscopic level,the theoretical literature to clarify this issue is lacking.To solve this problem,a quantum electro-dynamics(QED)-based analysis method is proposed.Combined with statistical physics,this method is used to analyze the vortex EM waves,and clarify the differences between the quantum and statistical OAMs.This paper includes the following main innovations:(1)the QED-based analysis method is combined with statistical physics to build a connection between the microscopic and macroscopic states of an EM wave;(2)with the proposed method,the statistical OAM vortex beam is comprehensively analyzed and compared with the quantum OAM vortex EM wave;and(3)the characteristics of the new physical dimension are stressed for quantum OAM to respond to the challenge of whether the vortex wave can provide the new independent dimension.This paper notes that the definitions of OAM with regard to the quantum OAM vortex EM wave and statistical OAM vortex beam are quite different,which belongs to the intrinsic and extrinsic OAMs,respectively.Consequently,the extrinsic OAM in the statistical OAM vortex beam is strongly coupled to the space domain of the electric field strength,which is the fundamental reason for the statistical OAM vortex beam transmission not exceeding the capacity bound of the conventional MIMO transmissions.In contrast,the intrinsic OAM in the quantum OAM transmission system is physically independent of the electric field strength and decoupled from the macroscopic space domain,constituting the new independent dimension of wireless transmissions.Therefore,the quantum OAM vortex EM wave with intrinsic OAM is a future direction for developing new resources of EM waves,as well as the potential key technology in the corresponding wireless communication systems.