Quantum Control of Electron-Hole Wave Packets in Semiconductor Nanostructures with Strong Terahertz Pulses

* 技术摘要 * 这项研究解决了凝聚态中光-物质相互作用的一个基本问题：在强电磁波的存在下，半导体中的量子态如何演变？迄今为止，半导体中带内跃迁（1-10 meV的低能激发）的量子动力学很少被探索;本项目的目标是建立量子动力学如何在多电子系统中展开的具体物理图像。强太赫兹脉冲与半导体纳米结构中的电子-空穴（e-h）波包相互作用，诱导发生在皮秒时间尺度上的带内跃迁。超快光/太赫兹探测脉冲不仅可以在时域中分辨量子态的振幅，还可以分辨量子态的相位，从而可以完全绘制出量子动力学。由于库仑相互作用支配量子动力学，时间分辨太赫兹研究将提供一个新的机会，了解库仑相关的e-h系统和多体激发的退相干。当太赫兹辐射强度超过一定强度时，光与物质相互作用的性质将发生质的变化，表现出场致电子和空穴运动的特征。这将为观察凝聚态物质中光-物质相互作用的量子-经典转变提供一个独特的平台。推广计划包括为K-12学生提供光学演示，为高中学生提供研究经验，为科学和数学教师提供专业发展机会。太赫兹（THz）波是频率介于微波和红外区域之间的电磁波。自然发生的太赫兹辐射充满了日常生活的空间，提供温暖，但这部分电磁频谱仍然是最少探索的区域。太赫兹科学技术是一个令人兴奋的前沿领域，具有广泛的应用前景。例如，THz光谱技术的独特和先进的技术已被证明是一个强大的工具，以研究材料的属性，直到最近还无法实现。光与半导体相互作用，可以产生带相反电荷的粒子，称为电子和空穴。当光学跃迁发生在能带隙附近时，带电粒子之间的吸引相互作用导致电子-空穴对的类氢系统的形成。太赫兹波与半导体中的电子-空穴对强烈相互作用，因为类氢系统在太赫兹频率下共振。在半导体纳米结构中，太赫兹相互作用可以引起电子-空穴对的特殊量子动力学行为。由此产生的量子动力学和相关的光学效应是非常感兴趣的，因为基本的物理过程具有广泛的应用超高速光电器件超过100 GHz。推广计划包括为K-12学生提供光学演示，为高中学生提供研究经验，为科学和数学教师提供专业发展机会。

****Technical Abstract****This research addresses a fundamental question of light-matter interactions in condensed matter: How do quantum states in semiconductors evolve in the presence of strong electromagnetic waves? Quantum dynamics of intraband transitions (low-energy excitations of 1-10 meV) in semiconductors are little explored to date; the objective of this project is to establish concrete physical pictures of how the quantum dynamics unfold in a many-electron system. Interacting with electron-hole (e-h) wave packets in semiconductor nanostructures, strong terahertz (THz) pulses induce intraband transitions occurring on a picosecond time scale. Ultrafast optical/THz probe pulses resolve not only the amplitude but also the phase of the quantum states in the time domain so that the quantum dynamics can be completely mapped out. Given that Coulomb interactions govern the quantum dynamics, the time-resolved THz study will provide a novel opportunity to understand Coulomb correlations in the e-h system and decoherence of many-body excitations. As the THz intensity exceeds a certain level, the nature of light-matter interactions will undergo a qualitative transition showing traits of the field-induced motion of electrons and holes. This will set a unique stage to observe the quantum-to-classical transition of light-matter interactions in condensed matter. The outreach programs include optics demonstrations for K-12 students, research experience for high school students, and professional development opportunity for science and math teachers.****Nontechnical Abstract****Terahertz (THz) waves are electromagnetic waves whose frequencies lie between the microwave and infrared regions. Naturally occurring THz radiation fills up the space of everyday life providing warmth, yet this part of the electromagnetic spectrum remains the least explored region. THz science and technology is a new and exciting frontier with a broad range of applications. For example, the unique and advanced techniques of THz spectroscopy have been proved to be a powerful tool to investigate the material properties inaccessible until recently. Interacting with a semiconductor, light can create oppositely charged particles, called electrons and holes. When the optical transition occurs near the energy band gap, the attractive interaction between the charged particles leads to the formation of a hydrogen-like system of an electron-hole pair. THz waves strongly interact with the electron-hole pair in semiconductors, because the hydrogen-like system is resonant at THz frequencies. The THz interaction can induce peculiar quantum dynamics of the electron-hole pair in semiconductor nanostructures. The resulting quantum dynamics and associated optical effects are of great interest because the fundamental physical processes have broad applications for ultrahigh-speed optoelectronic devices beyond 100 GHz. The outreach programs include optics demonstrations for K-12 students, research experience for high school students, and professional development opportunity for science and math teachers.