Tunneling and Activated Transitions in Driven Systems

9971537金：凝聚态物理项目将通过实验和理论来探索时间相关场对被困在双重或多重势阱中的粒子运动的影响，并将建立控制这种运动的方法。量子和经典多稳定系统对交变场的响应预计会显示出强烈的非线性，即使是相对较弱的场。目前的研究在很宽的光谱范围内考察了这种响应，从州际跃迁速率的频率到捕获粒子的特征阱内频率。高频场对激活跃迁速率的影响在很大程度上尚未被探索，正是在这个范围内，可以对颗粒运动进行最显著的选择性控制。两类实验，与紧密耦合的理论阐述，选择来证明这些和相关的现象。它们包括使用光学“镊子”驱动的光阱中经典粒子的阱间跃迁，以及用大振幅超声场探测无序金属中氢的量子隧穿。本研究计划的目标是通过实验和理论，探索时间相关场对被困在双重或多重势阱中的粒子运动的影响，并建立控制这种运动的方法。研究在很宽的光谱范围内考察了这种响应，从州际跃迁速率的频率到捕获粒子的特征井内频率。虽然这些想法和方法是基本的，但它们可以对应用科学和技术的几个领域产生实际影响。其中最令人兴奋的是控制非平衡晶体生长，其中表面扩散起着至关重要的作用。电子和光学元件的退化，由缺陷和杂质迁移带来的存在的振幅振荡场，是另一个。此外，化学和生物分离，一个巨大的增长领域，取决于在强场和场梯度中扩散的物种之间的区分。本研究明确包括研究生和本科生在实验和理论方面的参与。

9971537GoldingThe condensed matter physics project will explore, by experiment and by theory, the effects of time-dependent fields on the motion of particles trapped in double, or multiple, potential wells, and will establish ways of controlling this motion. Responses of both quantum and classical multi-stable systems to an alternating field are expected to display dramatically strong nonlinearity, even for comparatively weak fields. The present investigation examines this response over a wide spectral range, from frequencies of order of the rates of interstate transitions up to the characteristic intra-well frequencies of the trapped particle. The effect of a high-frequency field on the rates of activated transitions is largely unexplored, and it is in this range that the most striking, selective control over particulate motion can be exercised. Two classes of experiments, with closely coupled theoretical elaboration, are chosen to demonstrate these and related phenomena. They include inter-well transitions of classical particles in a driven optical trap using optical "tweezers", and the quantum tunneling of hydrogen in disordered metals probed by large amplitude ultrasonic fields.%%%The goal of this research program is to explore, by experiment and by theory, the effects of time-dependent fields on the motion of particles trapped in double, or multiple, potential wells, and to establish ways of controlling this motion. The investigation examines this response over a wide spectral range, from frequencies of order of the rates of interstate transitions up to the characteristic intra-well frequencies of the trapped particle. Although fundamental, the ideas and methods can result in practical consequences for several areas of applied science and technology. One of the most exciting occurs in control of nonequilibrium crystal growth, where surface diffusion plays a crucial role. The degradation of electronic and optical components, brought about by defect and impurity migration in the presence of large amplitude oscillating fields, is another. Also, chemical and biological separation, an area of immense growth, depends upon discriminating among species diffusing in strong fields and field gradients. This research explicitly includes both graduate and undergraduate participation in both experimental and theoretical aspects.