Putting A Spin On Machine Learning, Atom by Atom

没有什么能比得上磁铁的魔力。然而，即使是理查德·费曼，一个令人难以置信的天才科学传播者，也很难解释磁力是如何工作的。(The视频很容易在YouTube上找到。费曼对提出磁力问题的采访者有点不耐烦，这与很难在非物理学家--或者实际上是物理学家--能够很容易理解的水平上解释磁力的基本起源不无关系。）然而，科学家们现在不仅可以在原子的基础上测量力，而且我们可以利用和利用这些相同的力来操纵磁性，直到原子水平（甚至更高）。扫描探针显微镜是能够对磁力进行如此精细控制的仪器。探针显微镜是一种即将迎来四十岁生日的技术，它在概念上相当简单，而在实验上却不那么简单。一个非常尖锐的针尖，末端为单个原子或分子，被带到非常接近表面的位置，使得针尖与表面的距离为原子直径的量级或更小。这种原子级尖锐的探针可以在许多模式中使用，以逐个原子的方式探索、询问和修改下面的样品表面。一些最令人兴奋和突破性的科学曾经进行过涉及扫描探针显微镜的无与伦比的能力，不仅图像，但操纵，在单原子水平的问题。探针显微镜不仅限于原子的成像和控制;它们可以走得更远。通过适当修改尖端顶点，即使是电子的量子力学自旋-最终是磁性的来源-也可以通过探针和样品之间流动的微小电流检测到，或者，令人难以置信的是，通过测量单个原子之间的微小磁力。就在几个月前（2019年10月），IBM Almaden研究中心的Chris Lutz小组报告说，他们与韩国和牛津的研究人员合作，实现了对SPM所尝试的单个原子自旋状态的最精确和一致的控制。(It值得注意的是，IBM是扫描探针显微镜本身的诞生地，它是由宾尼格、罗勒和苏黎世Ruschlikon研究实验室的同事发明的，也是SPM驱动的单原子操纵的诞生地，这要归功于IBM Almaden的唐·埃格勒和同事们鼓舞人心的努力。）但是，探针显微镜工作者深藏的秘密是，他们很大一部分时间都花在强迫和哄骗探针提供原子分辨率上。然而，即使这还不够-当达到该分辨率时，显微镜工作者通常必须保持同时成像，移动和光谱询问单个原子的能力，同时始终注意尖端衍生的伪影。因此，探针显微镜的核心组件-探针本身-代表了该技术中的一个主要的、令人困惑的瓶颈。该项目集成了人工智能、表面科学和纳米科学，以消除探针显微镜的痛苦。我们将开发一个机器学习框架，从本质上讲，“自动聚焦”探针显微镜，然后将SPM带到它可以学习如何逐个原子和逐个自旋构建磁性纳米结构的位置。它自己。然后，这种支持人工智能的探针显微镜将用于执行一项极具挑战性的实验计划，其共同主题是在最基本的水平上控制磁性：单域，单分子，单原子和单自旋。

There is nothing quite like the magic of magnets. And yet even Richard Feynman, an incredibly gifted science communicator, struggled to explain just how magnetism works. (The video in question is easily found on YouTube. Feynman's slight tetchiness with the interviewer who raises the subject of magnetic forces is not entirely unrelated to the difficulty in explaining their fundamental origin at a level that a non-physicist -- or, indeed, a physicist -- can readily grasp.) Scientists are now at the point, however, where not only can we measure forces on an atom-by-atom basis, but we can harness and exploit those self-same forces to manipulate magnetism right down to the atomic level (and beyond). The instrument that allows this exquisite level of control of magnetic forces is the scanning probe microscope. A technique that will shortly reach its fortieth birthday, probe microscopy is conceptually rather straight-forward -- its experimental realisation rather less so. An exceptionally sharp tip, terminated in a single atom or molecule, is brought extremely close to a surface such that the tip-surface separation is of the order of the diameter of an atom or less. This atomically sharp probe can then be used in a number of modes to explore, interrogate, and modify the underlying sample surface on an atom-by-atom basis. Some of the most exciting and ground-breaking science ever carried out has involved the scanning probe microscope's unparalleled ability to not only image, but manipulate, matter at the single atom level. Probe microscopes are not just limited to the imaging and control of atoms; they can go much further. With an appropriately modified tip apex, even the quantum mechanical spin of electrons -- which, ultimately, is the source of magnetism -- is detectable either via the tiny electrical current that flows between the probe and the sample, or, incredibly, via measurement of the minuscule magnetic force between single atoms. Just a couple of months ago (in Oct. 2019), Chris Lutz' group at the IBM Almaden Research Centre reported that they have achieved, in collaboration with researchers in Korea and Oxford, the most precise and coherent control of the spin state of individual atoms ever attempted with SPM. (It's worth noting that IBM is the birthplace of both the scanning probe microscope itself, which was invented by Binnig, Rohrer and co-workers in the Ruschlikon, Zurich research labs, and of SPM-driven single atom manipulation, due to the inspiring efforts of Don Eigler and colleagues at IBM Almaden.) But the deep, dark secret of the probe microscopist is that a very large percentage of their time is spent coercing and cajoling the probe into providing atomic resolution. Yet even that's not enough -- when that resolution is achieved, the microscopist very often has to maintain the ability to image, move, and spectroscopically interrogate single atoms at the same time, while always being on the look-out for tip-derived artefacts. The component at the core of probe microscopy -- the probe itself -- therefore represents a major, and infuriating, bottleneck in the technique. This project integrates artificial intelligence, surface science, and nanoscience to take the pain out of probe microscopy. We will develop a machine learning framework that, in essence, "auto focuses" a probe microscope and then takes the SPM to the point where it can learn how to build magnetic nanostructures atom-by-atom and spin-by-spin. By itself. This AI-enabled probe microscope will then be used to carry out a programme of exceptionally challenging experiments whose common theme is the control of magnetism at the most fundamental levels: single domains, single molecules, single atoms, and single spins.