自由电子与原子晶格相互作用中的量子反冲，这一成果由新加坡南洋理工大学Liang Jie Wong课题组经过不懈努力而取得。相关论文发表在2023年1月19日出版的《自然—光子学》杂志上。

该课题组研究人员展示了量子反冲的实验演示，表明这种量子电动力学效应不仅在室温下可见，而且在其他电子散射机制的存在下也很稳健。通过在桌面平台上将自由电子从范德华材料的周期性二维原子片上散射出去，小组证明了只有量子反冲理论才能准确地预测X射线光子能量。该团队展示了量子反冲可以是巨大的，以至于经典预测的X射线光子被发射为极低能量的光子。

研究组设想量子反冲作为一种精确控制出射光子和电子能谱的手段，并表明量子反冲可以通过一系列参数进行定制：电子能量，原子组成和范德华材料的倾斜角度。他们的结果为利用和研究电子-光子相互作用中的量子电动力学效应的桌面室温平台铺平了道路。

据了解，带电粒子发出的光是许多科学现象和技术应用的基础。经典理论通过假设一个未偏转的带电粒子轨迹来确定发射的光子能量。1940年，Ginzburg指出，这一假设在量子电动力学中被打破，导致光子能量从经典的预测值中偏移(被称为量子反冲)。从那时起，自由电子发光过程中的量子反冲，包括切伦科夫辐射和史密斯-珀塞尔辐射，在理论上已经得到了很好的研究，但实验证明仍然是不确定的。

附：英文原文

Title: Quantum recoil in free-electron interactions with atomic lattices

Author: Huang, Sunchao, Duan, Ruihuan, Pramanik, Nikhil, Herrin, Jason Scott, Boothroyd, Chris, Liu, Zheng, Wong, Liang Jie

Issue&Volume: 2023-01-19

Abstract: The emission of light from charged particles underlies a wealth of scientific phenomena and technological applications. Classical theory determines the emitted photon energy by assuming an undeflected charged particle trajectory. In 1940, Ginzburg pointed out that this assumption breaks down in quantum electrodynamics, resulting in shifts—known as quantum recoil—in outgoing photon energies from their classically predicted values. Since then, quantum recoil in free-electron light-emission processes, including Cherenkov radiation and Smith–Purcell radiation, has been well-studied in theory, but an experimental demonstration has remained elusive. Here we present an experimental demonstration of quantum recoil, showing that this quantum electrodynamical effect is not only observable at room temperature but also robust in the presence of other electron-scattering mechanisms. By scattering free electrons off the periodic two-dimensional atomic sheets of van der Waals materials in a tabletop platform, we show that the X-ray photon energy is accurately predicted only by quantum recoil theory. We show that quantum recoil can be enormous, to the point that a classically predicted X-ray photon is emitted as an extremely low-energy photon. We envisage quantum recoil as a means of precision control over outgoing photon and electron spectra, and show that quantum recoil can be tailored through a host of parameters: the electron energy, the atomic composition and the tilt angle of the van der Waals material. Our results pave the way to tabletop, room-temperature platforms for harnessing and investigating quantum electrodynamical effects in electron–photon interactions.

DOI: 10.1038/s41566-022-01132-6

Source: https://www.nature.com/articles/s41566-022-01132-6