Tunneling and Activated Transitions in Driven Systems

9971537戈尔丁凝聚态物理学项目将通过实验和理论探索时间依赖场对被困在双或多个势威尔斯阱中的粒子运动的影响，并将建立控制这种运动的方法。量子和经典多稳态系统对交变场的响应，即使是相对较弱的场，也会显示出非常强的非线性。本调查研究这种响应在一个很宽的光谱范围内，从频率的顺序的速率的状态间转换的特征井内的频率被困粒子。高频场对激活跃迁速率的影响在很大程度上还未被探索，正是在这个范围内，可以对颗粒运动进行最引人注目的选择性控制。两类实验，密切耦合的理论阐述，被选择来证明这些和相关的现象。它们包括经典粒子在光镊驱动下的阱间跃迁和无序金属中氢的量子隧穿。本研究计划的目标是探索，通过实验和理论，时间依赖的领域对双，或多个，势威尔斯阱中捕获的粒子的运动的影响，并建立控制这种运动的方法。调查检查这种响应在一个很宽的光谱范围内，从频率的顺序的速率的状态间的转换到特性的井内频率的被困粒子。虽然是基本的，但这些思想和方法可以对应用科学和技术的几个领域产生实际影响。其中最令人兴奋的发生在控制非平衡晶体生长，表面扩散起着至关重要的作用。另一个问题是在大振幅振荡场存在下由缺陷和杂质迁移引起的电子和光学元件的退化。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别。这项研究明确包括研究生和本科生参与实验和理论方面。

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.