Physics Department and Solid State Institute, Technion-Israel Institute of Technology, Haifa, Israel.
Institut für Physik, Universität Rostock, Rostock, Germany.
Nature. 2019 Mar;567(7748):356-360. doi: 10.1038/s41586-019-0943-7. Epub 2019 Feb 18.
Topological phases enable protected transport along the edges of materials, offering immunity against scattering from disorder and imperfections. These phases have been demonstrated for electronic systems, electromagnetic waves, cold atoms, acoustics and even mechanics, and their potential applications include spintronics, quantum computing and highly efficient lasers. Typically, the model describing topological insulators is a spatial lattice in two or three dimensions. However, topological edge states have also been observed in a lattice with one spatial dimension and one synthetic dimension (corresponding to the spin modes of an ultracold atom), and atomic modes have been used as synthetic dimensions to demonstrate lattice models and physical phenomena that are not accessible to experiments in spatial lattices. In photonics, topological lattices with synthetic dimensions have been proposed for the study of physical phenomena in high dimensions and interacting photons, but so far photonic topological insulators in synthetic dimensions have not been observed. Here we demonstrate experimentally a photonic topological insulator in synthetic dimensions. We fabricate a photonic lattice in which photons are subjected to an effective magnetic field in a space with one spatial dimension and one synthetic modal dimension. Our scheme supports topological edge states in this spatial-modal lattice, resulting in a robust topological state that extends over the bulk of a two-dimensional real-space lattice. Our system can be used to increase the dimensionality of a photonic lattice and induce long-range coupling by design, leading to lattice models that can be used to study unexplored physical phenomena.
拓扑相能够实现材料边缘的受保护传输，使其免受无序和不完美的散射影响。这些相已经在电子系统、电磁波、冷原子、声学甚至力学中得到了证明，其潜在应用包括自旋电子学、量子计算和高效激光器。通常，描述拓扑绝缘体的模型是二维或三维的空间晶格。然而，在具有一个空间维度和一个合成维度（对应于超冷原子的自旋模式）的晶格中也观察到了拓扑边缘态，并且已经使用原子模式作为合成维度来证明晶格模型和物理现象，这些现象在空间晶格中是无法进行实验研究的。在光子学中，已经提出了具有合成维度的拓扑晶格来研究高维度和相互作用光子中的物理现象，但迄今为止，在合成维度中还没有观察到光子拓扑绝缘体。在这里，我们通过实验证明了在合成维度中的一种光子拓扑绝缘体。我们制造了一种光子晶格，其中光子在一个具有一个空间维度和一个合成模态维度的空间中受到有效磁场的作用。我们的方案支持这个空间模态晶格中的拓扑边缘态，从而产生一个在二维实空间晶格的大部分区域延伸的稳定拓扑态。我们的系统可以用于增加光子晶格的维度并通过设计诱导远程耦合，从而产生可以用于研究未知物理现象的晶格模型。
