近日，德国慕尼黑路德维希马克西米利安大学Andreas Tittl团队研究了时间对称破缺超表面共振的光学控制。2025年8月6日出版的《自然》杂志发表了这项最新研究成果。

有源超表面的可调性主要依赖于改变共振波长或增加材料损耗来分别使频谱失谐或猝灭谐振模式。然而，这两种方法都面临着基本的局限性，例如有限的Q因子和近场增强控制，以及无法通过将模式与远场完全耦合和解耦来实现谐振开关。

研究组通过超快光泵浦证明了超表面的时间对称性破缺，提供了辐射损耗驱动共振调谐的实验实现，实现了共振产生、湮灭、展宽和锐化。为了实现这种时间控制，研究组在连续体中引入了恢复的对称保护约束状态。即使它们的单位晶胞在几何上是不对称的，与辐射连续体的耦合仍然被完全抑制，在这项工作中，这是由两个同样强的反对称偶极子实现的。

通过在这些单元晶胞的部分进行选择性的米子共振泵浦，研究组可以修改它们的偶极子平衡来产生或湮灭共振，以及调整线宽、振幅和近场增强，从而在光学和量子通信、时间晶体和光子电路中具有潜在的应用。

附：英文原文

Title: Optical control of resonances in temporally symmetry-broken metasurfaces

Author: Aigner, Andreas, Possmayer, Thomas, Weber, Thomas, Antonov, Alexander A., de S. Menezes, Leonardo, Maier, Stefan A., Tittl, Andreas

Issue&Volume: 2025-08-06

Abstract: Tunability in active metasurfaces has mainly relied on shifting the resonance wavelength1,2 or increasing material losses3,4 to spectrally detune or quench resonant modes, respectively. However, both methods face fundamental limitations, such as a limited Q factor and near-field enhancement control and the inability to achieve resonance on–off switching by completely coupling and decoupling the mode from the far field. Here we demonstrate temporal symmetry breaking in metasurfaces through ultrafast optical pumping, providing an experimental realization of radiative-loss-driven resonance tuning, allowing resonance creation, annihilation, broadening and sharpening. To enable this temporal control, we introduce restored symmetry-protected bound states in the continuum. Even though their unit cells are geometrically asymmetric, coupling to the radiation continuum remains fully suppressed, which, in this work, is achieved by two equally strong antisymmetric dipoles. By using selective Mie-resonant pumping in parts of these unit cells, we can modify their dipole balance to create or annihilate resonances as well as tune the linewidth, amplitude and near-field enhancement, leading to potential applications in optical and quantum communications, time crystals and photonic circuits.

DOI: 10.1038/s41586-025-09363-7

Source: https://www.nature.com/articles/s41586-025-09363-7