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

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.