Switching in Driven Microscopic Systems

这个结合实验和理论的项目将探索由时间相关场驱动的模型物理系统中的热激活开关。潜在的理论思想是，场干扰开关动力学，因此可以强烈地影响开关概率。由于对这一过程的实验理解需要一个表征良好的物理系统，因此采用了在光诱导双阱势中捕获的介观粒子。该系统表现出类似于磁场中单畴纳米磁铁或电流偏置电阻分流约瑟夫森结的滞后响应的行为。然而，通过控制包含陷阱的激光束，可以很容易地调谐和调制三维限制势。阻尼率可以通过改变粒子特性或控制环境耦合来改变。理论研究可以对远离热平衡的系统的涨落过程提供更深入的理解。结果可以直接转移到当前重要的技术领域，例如，纳米磁随机存取存储器设备中的控制开关。参与这项研究的研究生和博士后将获得对激光、光学方法、实时计算、输运现象理论和非线性动力系统的理解，为他们从事科学和工程方面的教学和/或研究做好准备。开关事件在许多物理和生物过程中起着关键作用。在计算机硬盘上，信息被写入数十亿个微小的区域，1和0表示为纳米磁铁的方向。当信息被存储时，在这两种状态之间切换应该很容易，但它不应该自发发生，否则会导致记忆的丢失。在这项研究中，建立了一个由两束激光组成的双态开关模型。一束光可以将一个透明的亚微米粒子限制在空间的一个小区域内。当两束平行光束之间的距离小于粒子直径时，如果粒子获得足够的能量，它可以在两束光束之间切换。通过调制粒子的能量，可以控制跃迁速率，并定量研究开关发生的条件，即使在嘈杂的环境中也是如此。实验是用统计理论来分析的，这些理论将用于预测粒子在极端条件下的行为，即当粒子以快速和大振幅移动时。这些研究将导致控制随机开关过程的最佳方法，不仅应用于磁学，而且应用于化学和生物学。学生将接受光学、实时计算、凝聚态物质和统计物理方面的培训。

This combined experiment and theory project will explore thermally activated switching in model physical systems that are driven by time-dependent fields. The underlying theoretical idea is that a field interferes with switching dynamics and can therefore strongly affect switching probabilities. Since experimental understanding of this process requires a well-characterized physical system, the use of a mesoscopic particle trapped in an optically-induced double well potential is adopted. This system exhibits behavior analogous to the hysteretic response of a single-domain nanomagnet in a magnetic field or a current-biased resistively-shunted Josephson junction. However, the 3-dimensional confining potential can be readily tuned and modulated by controlling the laser beams comprising the trap. The damping rate can be varied by changing the particle properties or by controlling the environmental coupling. Theoretical studies can provide deeper understanding of fluctuation processes in systems driven far from thermal equilibrium. Results can be directly transferred to areas of current technological importance, for example, controlled switching in nanomagnetic random access memory devices. Graduate and postdoctoral students involved with this research will acquire understanding of lasers, optical methods, real-time computing, theory of transport phenomena and non-linear dynamical systems, preparing them for careers in teaching and/or research in science and engineering.%%%Switching events play a pivotal role in many physical and biological processes. On computer hard disks, information is written into billions of tiny regions with 1's and 0's expressed as the orientations of nanomagnets. Switching between these two states should be easy to do when information is stored but it should not happen spontaneously, which would lead to a loss of memory. In this investigation, a model of a two-state switch is created by two laser beams. A single beam can confine a transparent sub-micron particle to a small region in space. With two parallel beams separated by less than the particle diameter, the particle can switch between the two beams if it acquires enough energy. By modulating the energy of the particle, the transition rates can be controlled and the conditions under which switching occurs studied quantitatively, even in a noisy environment. The experiments are analyzed by statistical theories that will be developed to predict the particle's behavior under extreme conditions, i.e., when the particle is moved rapidly and with large amplitude. These studies should lead to optimal methods for controlling random switching processes with applications not only to magnetism but also to chemistry and biology. Students will receive training in optics, real-time computing, condensed matter and statistical physics.