AI 中文总结
研究人员利用可编程时空微带传输线平台，首次实验观测到超光速界面的双反射现象，验证了相关理论预测，解决了运动边界电动力学领域的长期谜题。
AI 中文摘要
一种超光速界面，即传播速度介于周围介质群速度之间的时空边界，可产生非互易放大、霍金辐射类比等特殊波动现象。一项特别引人关注的预测是，此类界面会将入射波分裂为三个出射波：一个透射波和两个反射波。然而，尽管已有数十年理论研究，由于对界面速度和调制速度的严格要求，这种三波散射现象始终未被实验观测到。本文引入可编程时空微带传输线平台，该平台可实现具有可控速度的阶跃调制超光速界面。利用该系统，我们首次直接观测到超光速界面的双反射现象，证实了一个透射波伴随两个不同反射波的出现。测量得到的频率和散射系数与长期以来的理论预测吻合良好。此外，我们揭示这两个反射波具有完全不同的因果对称性：一个是空间反演的，另一个是时间反演的。这些发现解决了运动边界电动力学中存在半个世纪的谜题，并建立了一个用于研究波动与动态界面相互作用的通用实验平台。本工作为开发与速度无关的散射器件、宽带频率转换及先进时空波动工程开辟了新途径。
英文摘要
An interluminal interface, a space-time boundary propagating at a velocity between the group velocities of the surrounding media, enables extraordinary wave phenomena such as nonreciprocal amplification and analogues of Hawking radiation. A particularly intriguing prediction is that such an interface splits an incident wave into three outgoing waves: one transmitted and two reflected. Yet, despite decades of theoretical study, this triple-wave scattering has remained experimentally unobserved, owing to stringent requirements on interface velocity and modulation speed. Here, we introduce a programmable spatiotemporal microstrip transmission-line platform that realizes step-modulated interluminal interfaces with controlled velocity. Using this system, we report the direct observation of bi-reflection from an interluminal interface, confirming the emergence of two distinct reflected waves alongside a transmitted one. Measured frequencies and scattering coefficients show excellent agreement with longstanding theoretical predictions. Furthermore, we reveal that the two reflections possess fundamentally different causal symmetries: one is spatially inverted, while the other is time-reversed. These findings resolve a half-century-old puzzle in moving-boundary electrodynamics and establish a versatile experimental platform for studying wave interaction with dynamic interfaces. Our work opens pathways to velocity-independent scattering devices, broadband frequency conversion, and advanced spatiotemporal wave engineering.
