Aigner Andreas, Possmayer Thomas, Weber Thomas, Antonov Alexander A, de S Menezes Leonardo, Maier Stefan A, Tittl Andreas
Chair in Hybrid Nanosystems, Faculty of Physics, Ludwig-Maximilians-University Munich, Munich, Germany.
Departamento de Física, Universidade Federal de Pernambuco, Recife-PE, Brazil.
Nature. 2025 Aug 6. doi: 10.1038/s41586-025-09363-7.
Tunability in active metasurfaces has mainly relied on shifting the resonance wavelength or increasing material losses 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.
有源超表面中的可调谐性主要依赖于分别改变共振波长或增加材料损耗，以在光谱上使共振模式失谐或淬灭。然而，这两种方法都面临着基本限制，比如品质因数有限、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共振的开-关切换。在此，我们通过超快光泵浦展示了超表面中的时间对称性破缺，实现了辐射损耗驱动的共振调谐的实验验证，能够实现共振的产生、湮灭、展宽和锐化。为实现这种时间控制，我们引入了连续统中恢复的对称性保护束缚态。尽管它们的晶胞在几何上是不对称的，但与辐射连续统的耦合仍然被完全抑制，在本工作中，这是通过两个同样强的反对称偶极子实现的。通过在这些晶胞的部分区域进行选择性米氏共振泵浦，我们可以改变它们的偶极平衡，以产生或湮灭共振，以及调节线宽、振幅和近场增强，从而在光通信和量子通信、时间晶体和光子电路等方面具有潜在应用。
