Brownian Transport Through Modulated Potential Energy Landscapes

本课程的重点是胶体粒子如何通过动态全息光学镊子创建的广泛势能景观移动。通过调制势能景观的输运是凝聚态物理中的一个经典问题，在各种系统中出现了各种变化，如流过第二类超导体的磁通，约瑟夫森结中的准粒子隧穿，以及生物分子马达中的进程。虽然关于一维周期势中的输运已知很多，但关于高维的调制布朗输运，特别是在非周期、准周期、随机和时变的地貌中，仍有更多的需要了解，所有这些都在自然和工业环境中扮演着重要的角色。之前理解这类过程的努力一直受到控制大多数相关系统的势能图景的困难，同时跟踪其微观组件的运动。动态全息光学镊子提供了一个独特的机会，通过以任何所需的配置投射多达数千个光学陷阱来构建微米级胶体粒子的任意一维、二维和三维势能景观。与大多数其他模型系统不同，使用数字视频显微镜可以精确地跟踪胶体颗粒的微观运动。光学操纵和高分辨率粒子跟踪的结合为研究受驱动的调制布朗输运提供了一个非常灵活和表征良好的模型系统，不仅对于单个粒子，而且对于强相互作用的粒子系统。除了从这类研究中获得的基本知识外，介观输运的特殊应用有望立即在纳米技术、生物技术和光子学中得到实际应用。电子如何通过金属玻璃的迷宫？DNA分子是如何穿过凝胶的？回答这些问题需要对物体如何穿越复杂的势能景观有一个新的基本见解。这些答案将立即对高温超导、药物发现、纳米技术和工程等领域产生实际影响。这个项目结合了最近引入的全息光学镊子(HOTS)所带来的最先进的微操作与精密数字视频显微镜，以提供这样的见解。该计划的核心是HOT能够从普通的激光光束创建任意定制设计的势能景观。这项技术使用计算机生成的全息图将光束加工成数千个单独的光学陷阱，每个陷阱都可以在计算机控制下在三维中独立移动。如果说单个光学陷阱可以比作《星际迷航》的拖拉机光束，那么全息光学镊子则更接近于全息甲板。微米级的胶体粒子穿过这样的光网络，可以找到长期存在的基本物理问题的解决方案。在这样做的过程中，它们也为实际应用提供了基础，例如利用光对蛋白质、DNA、纳米簇和活细胞进行分选。这个项目所基于的新技术是在高中生和本科生以及研究生和博士后的直接参与下开发的。这些学生在这些方法上的独特培训帮助他们在一流学校找到了职位，并在工业和学术界获得了长期工作。该项目的方法已经获得专利，这些专利导致了一个新的光学微操作产业的建立。产业界和各级学生的这种实质性参与将继续是该计划的中心主题。

This program focuses on how colloidal particles move through extensive potential energy landscapes created with dynamic holographic optical tweezers. Transport through modulated potential energy landscapes is a classic problem in condensed matter physics, with variants arising in systems as diverse as flux flow through type-II superconductors, quasiparticle tunneling in Josephson junctions and procession in biological molecular motors. While much is known about transport in one-dimensional periodic potentials, much more remains to be understood regarding modulated Brownian transport in higher dimensions, particularly in aperiodic, quasiperiodic, random, and time-varying landscapes, all of which figure heavily in natural and industrial settings. Previous efforts to understand such processes have been hampered by the difficulty of controlling most relevant systems' potential energy landscapes while tracking their microscopic components' motions. Dynamic holographic optical tweezers present a unique opportunity to construct arbitrary one-, two-, and three-dimensional potential energy landscapes for micrometer-scale colloidal particles by projecting up to several thousand optical traps in any desired configuration. Unlike most other model systems, colloidal particles' microscopic motions can be tracked with exquisite accuracy using digital video microscopy. The combination of optical manipulation and high-resolution particle tracking provides an extraordinarily flexible and well-characterized model system for studying driven modulated Brownian transport, not only for single particles but also for strongly interacting systems of particles. In addition to the fundamental knowledge gained from such studies, the particular application to mesoscopic transport promises immediate practical applications in nanotechnology, biotechnology, and photonics.How does an electron find its way through the labyrinth of a metallic glass? How does a DNA molecule thread through a gel? Answering such questions requires a new fundamental insights into how objects traverse complicated potential energy landscapes. And the answers will have immediate practical ramifications for fields as diverse as high-temperature superconductivity, drug discovery, nanotechnology and engineering. This program combines state-of-the-art micromanipulation made possible by the recent introduction of holographic optical tweezers (HOTs) with precision digital video microscopy to provide just such insights. The heart of this program is provided by HOT's ability to create arbitrary custom-designed potential energy landscapes from an ordinary beam of laser light. The technique uses computer-generated holograms to craft the beam into thousands of individual optical traps, each of which can be moved independently in three dimensions under computer control. If a single optical trap can be likened to Star Trek's tractor beam, then holographic optical tweezers more closely resemble the holodeck. Micrometer-scale colloidal particles driven through such latticeworks of light trace out solutions to long-standing fundamental physics questions. In so doing, they also provide the basis for practical applications such as sorting proteins, DNA, nanoclusters, and living cells using light. The new techniques on which this program is based were developed with direct involvement of high school and undergraduate students, as well as graduate students and postdocs. These students' unique training in these methods has helped them to land positions in top-rated schools, as well as long-term employment in industry and academia. This program's methods have been patented, and the patents have led to the foundation of a new industry in optical micromanipulation. Such substantive involvement of industry and students at all levels will continue to be a central theme of this program.