Quantum Coherence and Tunneling in Semiconductor Nanostructures

本论文主要研究低维隧道结和可调谐半导体量子点的相位相干特性。这些系统将相互竞争的零维、一维和二维状态并置在一起，这些状态被精确的纳米级屏障隔开。量子隧穿混合并增强了简并基态之间的耦合，导致纳米尺度器件中长寿命量子相干的潜在发展。在固态环境中精确控制和探测量子态仍然是当今凝聚态物理学的重要挑战。在这些系统中，宏观量子相干性的发展来自于打破基本对称性的量子相变。纳米结构环境中的相位相干系统的基本物理在很大程度上是未开发的，占主导地位的退相干机制未知，目前没有详细的理论模型。提出了一系列电学、隧穿和动力学测量方法来研究纳米尺度半导体器件中电子的量子相干输运。这项工作的一个重要特点是制造和表征的隧道结的障碍下降到几个晶格间距。参与该项目的本科生和研究生将接受最先进的制造和表征技术的培训。本课程旨在培养学生为企业、工业或政府部门的职业生涯做好准备。本研究的重点是研究纳米级半导体器件中电子的量子力学相互作用所产生的量子相干现象。量子力学相干性通常难以维持较长的时间，因为耦合到外部扰动和存在的缺陷。这些系统中的量子相干性来自于半导体纳米结构制造的最新进展。在这些前所未有的干净系统中，理论预测量子相变进入新的集体状态，可以维持异常长寿命的激发。提出了设计用于探测和表征假设量子态的电气和高频测量。量子态的控制和操纵可以用于量子信息处理中的应用，这是一个越来越重要的技术领域。潜在的应用包括量子计算、量子密码学和在固态环境中检验爱因斯坦-波多尔斯基-罗森（EPR）悖论。参与这项研究的本科生和研究生在最先进的制造和表征技术方面接受广泛的培训，并可以从事工业或基础研究。

This work focuses on the study of phase coherent properties of low-dimensional tunnel junctions and tunable semiconductor quantum dots. These systems juxtapose competing zero-, one- and two-dimensional states separated by a precise, nanometer-scale barriers. Quantum tunneling mixes and enhances the coupling between the degenerate ground states, leading to potential development of long-lived quantum coherence in nanometer scale devices. Precise control and detection of quantum states within solid-state environment remain important challenges in condensed matter physics today. The development of macroscopic quantum coherence in these systems arises from quantum phase transitions that break the underlying symmetry. The underlying physics of phase coherent systems in nanostructured environment is largely unexplored, the dominant decoherent mechanisms unknown, and no detailed theoretical model is currently available. A series of electrical, tunneling, and dynamical measurements to study the quantum coherent transport of electrons in nanometer-scale semiconductor devices is proposed. An important feature of the work is fabrication and characterization of tunnel junctions with barriers down to few lattice spacings. Undergraduate and graduate students involved in the project will receive training in the state of art fabrication and characterization techniques. This training is intended to prepare them for careers in academe, industry or government.This research is centered on the study of quantum coherent phenomena arising from quantum mechanical interplay of electrons in nanometer-scale semiconductor devices. Quantum mechanical coherence is normally difficult to sustain for extended period of time because of coupling to the external perturbations and presence of imperfections. The quantum coherence in these systems derives from recent advances in fabrication of semiconductor nanostructures. In these unprecedentedly clean systems, theories predict quantum phase transitions into novel collective states that can sustain exceptionally long-lived excitations. Electrical and high frequency measurements designed to probe and characterize the postulated quantum states are proposed. Control and manipulation of quantum states can be exploited for applications in quantum information processing, a field of increasing technological importance. Potential applications include quantum computation, quantum cryptography, and test of Einstein-Podolsky-Rosen (EPR) paradox within a solid state environment. Undergraduate and graduate students participating in this research receive broad training in the state of art fabrication and characterization techniques and can pursue careers in industrial or fundamental research.