Nonlinear Dynamics in Quantum Wells at Terahertz Frequencies

这个项目将探索量子阱在太赫兹频率下的非平衡和非线性特性。目的是观察宽量子阱结构中的固有光学双稳性、周期加倍、混沌和拉比振荡。这些效应最近已经通过计算机模拟预测，使用哈特里近似，模拟了包含许多电子的量子阱，这些量子阱受到强烈的太赫兹辐射。实验将使用加州大学圣巴巴拉分校的自由电子激光器进行。专门为量子混沌实验量身定制的半导体结构将与加州大学圣巴巴拉分校的合作者合作生长和表征。近年来，许多研究者一直在努力调和量子力学与牛顿动力学中混沌的存在。这个领域被称为“量子混沌”。研究“量子混沌”的传统方法是研究经典动力学为混沌的系统的量子力学。这个项目采取了一种不同的方法，专注于寻找混沌运动的纯量子力学版本。也就是说，运动是混沌的，但在经典力学中没有类似的运动。要研究的系统是被限制在半导体量子阱的薄层中的电子，它们被每秒振荡数万亿次的极强的场驱动。仿真结果表明，这类系统可以表现出没有经典模拟的混沌运动。这些强磁场是由加州大学圣巴巴拉分校独特的自由电子激光器产生的。该项目最初将寻求观察混沌的前兆，称为分岔，其中一个参数的微小变化（例如，振荡场的强度）会导致运动特征的巨大变化。直接感兴趣的分支是所谓的“周期加倍”，在这种情况下，系统的振荡发生在驱动场振荡周期的两倍。找到这样的分岔后，该项目将在量子系统中寻找混沌运动。＊＊＊

w:\awards\awards96\*.doc 9623874 Sherwin This project will explore non-equilibrium and non linear properties of quantum wells at Terahertz frequencies. The objective is to observe intrinsic optical bistability, period- doubling, chaos and Rabi oscillations in wide quantum well structures. These effects have recently been predicted by computer simulations using the Hartree approximation which have modeled quantum wells containing many electrons and which are subject to intense Terahertz radiation. The experiments will be performed using the UC Santa Barbara Free-Electron Laser. Semiconductor structures which are specially tailored for the quantum chaos experiments will be grown and characterized in collaboration with collaborators at UC Santa Barbara. %%% In recent years, many investigators have been struggling to reconcile quantum mechanics with the existence of chaos in Newtonian dynamics. The field is called 'quantum chaos'. The traditional approach to 'quantum chaos' is to study the quantum mechanics of systems whose classical dynamics are chaotic. This project takes a somewhat different approach and focuses on a search for a purely quantum mechanical version of chaotic motion. That is, motion that is chaotic, but has no analogue in classical mechanics. The system to be studied are electrons confined in thin layers of semiconductor quantum wells, and which are driven by extremely strong fields which oscillate several trillion times each second. Simulations indicate that such systems can exhibit a chaotic motion with no classical analogue. The strong fields are generated by UC Santa Barbara's unique Free-Electron Laser. The project will initially seek to observe precursors of chaos, called bifurcations, in which a small change in a parameter (for example, the strength of the oscillating field) causes a dramatic change in the character of motion. A bifurcation of immediate interest is so-called "period-doubling", in which the system's oscillations occur at twice the period of oscillations in the driving field. Having found such bifurcations, the project will then seek chaotic motion in a quantum system. ***