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已有 1182 次阅读 2023-1-24 15:23 |个人分类:新观察|系统分类:博客资讯




Fig. 1 Light can be shaped into a structure resembling a twisted smoke ring. Credit: Y. Shen and Z. Zhu.


Fig. 2 (a) The parameter-space sphere which represents spin: the longitude and latitude degrees (α and β) of a parametric 2-sphere are represented by hue color and its lightness (dark towards the south pole, where spin is down, and bright towards the north pole, where spin is up). Each point on a parametric 2-sphere corresponds to a closed iso-spin line located in a 3D Euclidean space. (b) The lines projected from the selected points of the same latitude β and different longitude α on the hypersphere (highlighted by the solid dots with the corresponding hue colors), form torus knots covering a torus (with different tori corresponding to different β). (c) The real-space visualization of a Hopf fibration as a full stereographic mapping from a hypersphere: torus knots arranged on a set of coaxially nested tori, with each torus corresponding to different latitude β of a parametric 2-sphere. The black circle corresponds to the south pole (spin down) and the axis of the nested tori corresponds to the north pole (spin up) in (a). (d) The 3D spin distribution in a hopfion, corresponding to the isospin contours in (c) with each spin vector colored by its α and β parameters of a parametric sphere in (a) as shown in the insert. (e, f) The cross-sectional view of the spin distribution in (d): (e) xy (z = 0) and (f) yz (x = 0) cross-sections show skyrmion-like structures with the gray arrows marking the vorticity of the skyrmions. Color scale is the same as that corresponding to the spin direction in (d). Credit: Shen et al., doi 10.1117/1.AP.5.1.015001

据国际光学工程学会(SPIE2023119日报道,光子霍普夫子:形状像烟圈,行为像粒子的光(Photonic hopfions: Light shaped as a smoke ring that behaves like a particle)。光可以被塑造成一个类似于扭曲的烟圈的结构(1)。

在我们的日常生活中,我们经常能发现一种局部的波结构,它在传播时保持其形状就像在空气中飞行的烟圈。类似的稳定结构已经在不同的研究领域进行了研究,可以在磁铁、核系统和粒子物理中找到。与烟圈相比,它们可以使其对扰动具有弹性。这在数学和物理学中被称为拓扑保护(topological protection)。

一个典型的例子是磁性薄膜中磁场的纳米飓风般的纹理(nanoscale hurricane-like texture),表现为粒子——也就是说,不改变它们的形状——被称为斯格明子(skyrmions)。三维空间中类似的环状(或环形)图案,将波的各种属性的复杂空间分布可视化,称为霍普夫子(hopfions)。用光波(light waves)实现这样的结构是非常难以捉摸的。

最近的结构光的研究揭示了强烈的偏振,相位和振幅的空间变化,这使理解-并开辟了设计的机会-拓扑稳定的光学结构的行为像粒子。这种具有不同拓扑性质的准粒子可能具有巨大的潜力,例如作为下一代超大容量的光信息传输以及在量子技术中的信息载体。相关研究结果于2023110日已经在《高级光子学》(Advanced Photonics)杂志网站发表——Yijie Shen, Bingshi Yu, Haijun Wu, Chunyu Li, Zhihan Zhu, and Anatoly V. Zayats. Topological transformation and free-space transport of photonic hopfions. Advanced Photonics, Published: 10 January 2023, 5(1): 015001. DOI: 10.1117/1.AP.5.1.015001. https://doi.org/10.1117/1.AP.5.1.015001

参与此项研究的有来自英国南安普敦大学(University of Southampton, United Kingdom)、中国哈尔滨理工大学(Harbin University of Science and Technology, China)以及英国伦敦大学国王学院(King’s College London, United Kingdom)的研究人员。来自英国和中国的物理学家在此论文中展示了在三维空间中具有设计的拓扑稳定特性的偏振图案的生成,并且首次实现了在自由空间中的可控变换和传播。

由于这一见解,提供了几个重大进展和新的观点。该论文的主要作者、英国南安普顿大学的沈义杰(Yijie Shen音译)说:“我们报告了一种新的、非常不寻常的3D拓扑孤子(3D topological solitons)结构光家族,光子霍普夫子(photonic hopfions),其中拓扑纹理和拓扑数可以自由和独立地调整,远远超出了之前描述的最低阶固定拓扑纹理。”

“我们的研究结果说明了光结构的巨大之美。我们希望它们将激发拓扑保护光配置在光通信、量子技术、光与物质相互作用、超分辨率显微镜和计量学中的潜在应用的进一步研究,”伦敦大学国王学院教授、项目负责人阿纳托利·扎亚特(Anatoly Zayats)说。

本工作提供了一个理论背景,描述了这类霍普夫(Hopfions)家族的出现以及它们的实验生成和表征,揭示了一种拓扑保护极化纹理的丰富结构。与以前观察到的局限于固态材料中的霍普夫子(Hopfions)相比,这项工作证明,与直觉相反的是,一个光霍普夫子(optical hopfion)可以在极化分布的拓扑保护下在自由空间(free space)中传播。所研究的光子霍普夫子(photonic hopfions)在传播过程中的鲁棒拓扑结构(robust topological structure)是应用中经常寻求的。


本研究得到了中国国家自然科学基金项目(National Natural Science Foundation of China, Grant Nos. 62075050, 11934013, and 61975047),中国黑龙江省高层次人才计划项目(High-Level Talents Project of Heilongjiang Province, China, Grant No. 2020GSP12);欧洲研究委员会iCOMM项目(European Research Council iCOMM project, Grant No. 789340)的资助。


Topological near fields generated by topological structures


Structured light fields embody strong spatial variations of polarization, phase, and amplitude. Understanding, characterization, and exploitation of such fields can be achieved through their topological properties. Three-dimensional (3D) topological solitons, such as hopfions, are 3D localized continuous field configurations with nontrivial particle-like structures that exhibit a host of important topologically protected properties. Here, we propose and demonstrate photonic counterparts of hopfions with exact characteristics of Hopf fibration, Hopf index, and Hopf mapping from real-space vector beams to homotopic hyperspheres representing polarization states. We experimentally generate photonic hopfions with on-demand high-order Hopf indices and independently controlled topological textures, including Néel-, Bloch-, and antiskyrmionic types. We also demonstrate a robust free-space transport of photonic hopfions, thus showing the potential of hopfions for developing optical topological informatics and communications.


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