Quantum Coherence and Dynamical Instability in Quantum Wells Driven by Intense Terahertz Fields.

*非技术摘要*自早期人类利用火取暖和取光以来，对电磁辐射的控制一直是我们人类发展的核心。电磁辐射的概念已有近150年的历史，由麦克斯韦于1865年提出，并于1866年发现无线电波。在近50年的时间里，无线电波在很大程度上一直是实验室里的奇葩。很难想象没有无线电波、微波、热、光和X射线的现代生活，这些现在都被理解为电磁辐射的表现形式，按频率递增的顺序列出。然而，介于微波频率和热频率之间的是所谓的“太赫兹差”，频率范围从0.1到10万亿周/秒(0.1-10太赫兹)。电磁波存在于这个频率范围内，但它们极难产生和控制。这一个人研究人员奖支持一个项目，该项目将使用加速器驱动的自由电子激光产生的世界上最亮的太赫兹波脉冲来搜索预计将在纳米厚度的半导体设备中出现的新量子力学现象。正在研究的半导体器件类似于光纤通信中用于调制光的器件，以及蜂窝电话中的超快晶体管。该项目将支持两名博士生以及本科生和高中实习生的教育。这些学生将学习最先进的技术来产生和操纵整个电磁谱的电磁辐射，为他们在国家科学和技术劳动力中的领导地位做好准备，并使人类更接近于为未来的技术利用太赫兹辐射。*技术摘要*频率在1至5太赫兹之间的强振荡电场越来越多地出现在实验室中，甚至在太赫兹量子级联激光器这样的芯片级联器件中也是如此。越来越多的理论预测，在强THz场驱动的半导体量子阱中将出现令人着迷的、潜在有用的现象。例如，基于多电子系统常用近似的计算预测，在实验可实现的条件下，掺杂量子阱中可能会出现混沌动力学。在一个明显的量子系统上的实验中观察到混沌动力学将非常令人惊讶，因为混沌是由非线性产生的，而量子力学是一个线性理论。该项目将支持对掺杂量子阱中混沌动力学前驱的实验研究。这些实验所需的强烈太赫兹辐射将由加州大学圣巴巴拉分校和德国德累斯顿的自由电子激光产生。该项目还将支持研究强太赫兹辐射如何改变半导体和半导体量子井的量子态和能带结构，通过太赫兹引起的近红外吸收和发射的变化来测量。两名博士生将接受半导体物理、纳米制造、太赫兹光学、近红外和可见光频率、机械设计、低温、电子学和实验室仪器的计算机控制以及国际合作方面的深入而广泛的培训，为他们在国家科学和技术劳动力中的领导地位做好准备。受资助的博士生还将指导一批不同的本科生研究人员和高中生实习生，激发他们在科学或工程领域追求职业生涯的兴趣。

****NON-TECHNICAL ABSTRACT****Beginning when early humans harnessed fire for heat and light, the control of electromagnetic radiation has been central to the development of our species. The notion of electromagnetic radiation is nearly 150 years old, proposed by Maxwell in 1865 and demonstrated with the discovery of radio waves in 1866. Radio waves remained largely a laboratory curiosity for nearly 50 years. It is difficult to imagine modern life without radio waves, microwaves, heat, light, and X-rays, which are now all understood to be manifestations of electromagnetic radiation, listed in order of increasing frequency. However, lying between the frequencies of microwaves and heat, stretching from 0.1 to 10 trillion cycles per second (0.1-10 terahertz) is the so-called 'terahertz gap.' Electromagnetic waves exist in this frequency range, but they are extremely difficult to generate and control. This individual investigator award supports a project that will use the world's brightest pulses of terahertz waves, generated by accelerator-driven 'free-electron lasers', to search for new quantum-mechanical phenomena predicted to occur in nanometers-thick semiconductor devices. The semiconductor devices under study are similar to those used to modulate light in fiber-optic communications, and as ultrafast transistors in cellular telephones. This project will support the education of two PhD students, as well as undergraduate and high-school interns. The students will learn the most advanced techniques to generate and manipulate electromagnetic radiation across the electromagnetic spectrum, preparing them for leadership in the nation's scientific and technological workforce, and bringing mankind closer to harnessing terahertz radiation for future technologies. ****TECHNICAL ABSTRACT****Strong oscillating electric fields with frequencies between 1 and 5 THz are increasingly available in laboratories and even inside chip-scale devices like terahertz quantum cascade lasers. A growing body of theory predicts that fascinating and potentially useful phenomena will occur in semiconductor quantum wells driven by strong THz fields. For example, calculations based on commonly used approximations for many-electron systems predict that chaotic dynamics can occur in doped quantum wells for experimentally-achievable conditions. The observation of chaotic dynamics in an experiment on a manifestly quantum system would be very surprising, since chaos arises from nonlinearities while quantum mechanics is a linear theory. This project will support experimental searches for precursors of chaotic dynamics in doped quantum wells. The intense terahertz radiation necessary for these experiments will be generated by free-electron lasers at UC Santa Barbara and in Dresden, Germany. This project will also support studies of how strong terahertz radiation changes the quantum states and band structure of semiconductors and semiconductor quantum wells, as measured by terahertz-induced changes in the near-infrared absorption and emission. Two PhD students will receive deep and broad training in semiconductor physics, nanofabrication, optics at terahertz, near-IR and visible frequencies, mechanical design, cryogenics, electronics, and computer control of laboratory instrumentation, as well as in international collaboration, preparing them for leadership in the nation's science and technology workforce. The supported PhD students will also mentor a diverse group of undergraduate researchers and high-school student interns, sparking their interest in pursuing careers in science or engineering.