The physics and technology of low-dimensional electronic systems at terahertz frequencies

在过去的20年里，对介观量子限制电子系统的研究揭示了大量令人兴奋的基础物理学。随着设备制造和测量技术的进步，这些研究没有任何减弱的迹象，因为可以进行更复杂的结构和更复杂的实验。在许多重要的介观器件中，如二维电子系统、层状半导体结构、半导体量子点、横向限制线、点和其他几何形状，其特征能量尺度对应于太赫兹（THz）频率范围（1thz = 1x10^12 Hz = 4.1 meV），直到最近才难以获得。此外，尽管大多数介观系统的研究都使用直流输运或光学（近红外）技术，但关于凝聚态系统中载流子的状态和动力学的宝贵信息，无法通过直流输运方法获得，可以通过动态（高频）电子响应获得。我们的愿景是通过开发和利用太赫兹频率技术，特别是导波技术，来探测量子限制电子系统的太赫兹频率/皮秒响应，从而在介观电子系统的研究中创造一个阶跃变化。我们将开发准光学技术，以产生（并检测）低温恒温器中邻近介观系统的单周期太赫兹/皮秒电子脉冲，避免以前高频（高达千兆赫范围）电测量中固有的RC带宽限制问题。我们还将开发执行皮秒分辨率测量的方法，能够比以前更快地监测单个电子的空间位置三个数量级；这将为介观物理领域提供一种通用技术，其中量子态的开始或变化发生在皮秒时间尺度上。该项目是量子有限电子系统中太赫兹频率科学与技术的共生发展，将是国际上独一无二的，并将为介观物理学开辟一个重要的新方向。

Over the last 20 years, the study of mesoscopic quantum-confined electronic systems has revealed a wealth of exciting and fundamental physics. These studies show no sign of abating as advances in device fabrication and measurement techniques enable ever more intricate structures and more sophisticated experiments to be made. The characteristic energy scale in many important mesoscopic devices such as two-dimensional electron systems, layered semiconductor structures, semiconductor quantum dots, and laterally-confined wires, dots, and other geometries, corresponds to the terahertz (THz) frequency range (1 THz = 1x10^12 Hz = 4.1 meV), which until recently has been difficult to access. Furthermore, although the majority of studies of mesoscopic systems use dc transport or optical (near-infrared) techniques, invaluable information on the states and dynamics of carriers in condensed matter systems, not obtainable by dc transport methods, can potentially be accessed though the dynamic (high frequency) electronic response. Our vision is to create a step-change in the study of mesoscopic electronic systems by developing and exploiting THz fre-quency technology, and in particular, guided-wave techniques, to probe the THz frequency / picosecond response of quantum-confined electronic systems. We will develop quasi-optical techniques to generate (and detect) single-cycle THz / picosecond electronic pulses adjacent to the mesoscopic system in the cryostat, avoiding the RC bandwidth-limiting problems inherent in previous high frequency (up to the gigahertz range) electrical measurements. We will also develop the methodology to perform picosecond-resolution measurements capable of monitoring the spatial position of single electrons three orders-of-magnitude faster than achieved previously; this will provide a generic technology for the field of mesoscopic physics where the onset of, or change in, a quantum state occurs on a picosecond time scale. This programme, which comprises the symbiotic development of THz frequency science and technology in quantum con-fined electronic systems, will be unique internationally and will open an important new direction for mesoscopic physics.