二维切连科夫辐射的观测
Observation of 2D Cherenkov radiation
AI总结：
首次观测二维切连科夫辐射，揭示自由电子在二维中发射量子化光子，实现前所未有的量子耦合强度。
摘要：
在超过80年的研究中，自由电子辐射现象的传统描述，如切连科夫辐射，一直未变：经典三维电磁波。有趣的是，在降维情况下，自由电子辐射的性质被预测会根本性地改变。在这里，我们首次观测到切连科夫表面波，其中自由电子发射窄带宽的光子准粒子，其在二维中传播。低维度性和窄带宽使得通过电子能量损失光谱可以识别量子化的发射事件。我们的结果支持最近的理论预测，即自由电子并不总是发射经典光，而是可以与它们发射的光子纠缠。二维切连科夫相互作用实现了超过以往报告两序 magnitude 的量子耦合强度，首次达到单电子-单光子相互作用的 regime。我们的发现为自由电子量子光学中以前未探索的现象铺平了道路，促进了明亮的自由电子基量子发射器，可用于 heralded Fock 状态。
英文摘要：
For over 80 years of research, the conventional description of free-electron radiation phenomena, such as Cherenkov radiation, has remained unchanged: classical three-dimensional electromagnetic waves. Interestingly, in reduced dimensionality, the properties of free-electron radiation are predicted to fundamentally change. Here, we present the first observation of Cherenkov surface waves, wherein free electrons emit narrow-bandwidth photonic quasiparticles propagating in two-dimensions. The low dimensionality and narrow bandwidth of the effect enable to identify quantized emission events through electron energy loss spectroscopy. Our results support the recent theoretical prediction that free electrons do not always emit classical light and can instead become entangled with the photons they emit. The two-dimensional Cherenkov interaction achieves quantum coupling strengths over two orders of magnitude larger than ever reported, reaching the single-electron-single-photon interaction regime for the first time with free electrons. Our findings pave the way to previously unexplored phenomena in free-electron quantum optics, facilitating bright, free-electron-based quantum emitters of heralded Fock states.
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