Dynamics and its coherent control of equilibrium and nonequilibrium electrons in semiconductor quantum structures

本项目研究的目的是通过开发基于量子点中单太赫兹光子探测技术的新型测量方法，加深对半导体量子结构物理的理解，并探索控制半导体多体系统量子态的方法。第一类的成就是（i）通过使用超高灵敏度探测器开发具有前所未有的灵敏度和空间分辨率的新型扫描型太赫兹显微镜，以及（ii）通过应用显微镜研究量子霍尔器件中的非平衡电子产生动力学。最大的成就是通过将量子点太赫兹光子探测器集成到扫描显微镜（空间分辨率，50 □m）中实现了太赫兹光子计数技术：通过应用测量系统，量子霍尔棒在热点（电子入口和出口角）的非平衡电子产生动力学，栅极偏置引起的势垒和边缘状态。第二类成果是基于利用量子霍尔条中的自旋分裂边通道实现对核自旋系统的电操纵，即，核自旋极化已经产生，相干控制，并通过边缘通道灵敏地检测：通过利用这些效应，一种新的核自旋显微镜与纳米分辨率已经开发。应用该技术，我们以纳米级的精度阐明了GaAs量子霍尔棒中的局域核自旋极化，并揭示了其产生和扩散的动力学过程。此外，发现边缘态沟道处的束缚势斜率对产生核自旋极化的效率有重要影响，这为用核自旋极化探针探测量子霍尔边缘沟道开辟了新的可能性.

The purpose of the project research is to achieve deeper understanding of the physics of semiconductor quantum structures by developing novel measurement methods based on the technique of single-terahertz-photon detection in quantum dots, and to explore the method of controlling quantum states of semiconductor many body systems. The achievements in the first category are (i) the development of novel scanning-type terahertz microscopes with unprecedented sensitivity and spatial resolution by using ultra-highly sensitive detectors and (ii) the study of dynamics of non-equilibrium electron generation in quantum Hall devices by applying the microscopes. The biggest achievement is the realization of a terahertz photon-counting technique by incorporating quantum-dot terahertz-photon detectors into scanning microscopes (spatial resolution, 50 □m): By applying the measurements systems, dynamics of non-equilibrium electron generation of quantum Hall bars at hot spots (electron entry and exit corners), gate-bias induced potential barriers, and edge states. The achievements in the second category are based on the realization of electrically manipulating nuclear spin system by using spin-split edge channels in quantum Hall bars; viz., nuclear-spin polarization has been generated, coherently controlled, and sensitively detected by means of the edge channels: By exploiting these effects, a novel nuclear-spin microscopy with a nano-meter resolution has been developed. By applying the technique, local nuclear-spin polarization in GaAs quantum Hall bars has been clarified with nano-meter accuracy, and the dynamics of its generation and diffusion have been unveiled. In addition, it is found that the slope of confining potential at the edge states channels crucially affects the efficiency of generating nuclear spin polarization, opening up the new possibility of probing quantum Hall edge channels with the probe of nuclear spin polarization.