Measuring Quantum Dot Interactions Using Coherent Two-Dimensional Spectroscopy

非技术摘要半导体量子点具有与原子中的能级相似的离散能级，因此它们经常被描述为“人造原子”。与原子不同，量子点的能级结构可以进行工程设计，使其在从高效激光到量子信息处理的广泛应用中具有吸引力。此外，量子点可以嵌入固态设备中，这是应用程序中使用的一个关键功能。当量子点相互靠近时，它们的相互作用会产生新的状态，就像原子之间的相互作用导致分子的形成一样。这个项目将使用一种新的相干光学方法来观察和表征量子点之间的相互作用，并具有足够的空间分辨率来分离单个点或一小组相互作用的点。这种新的光学方法的灵感来自于已建立的用于确定分子结构的磁共振技术。此外，该项目开发的光谱技术将有更广泛的应用。例如，它可以用来研究光伏太阳能电池中的激发过程。该项目将通过培训固态系统相干光谱学多学科领域的学生，将研究和教育结合起来。这项培训将包括凝聚态系统与光相互作用的基础科学以及光子学和微制造的实用方面。技术摘要通过分子束外延生长的半导体量子点可能应用于从低阈值激光二极管到实现量子信息科学中的量子比特。利用单点技术对外延生长的量子点进行了广泛的研究，但单点技术不能很好地探测量子点之间的耦合。相互作用可以极大地改变量子点的光学和电学性质。此外，量子信息方案要求量子比特之间存在可控的相互作用，从而要求量子点之间存在可控的相互作用。本项目使用一种基于光电流读出的光学多维相干谱的新实现方式来探索量子点之间的耦合，并将其应用于InGaAs量子点的小集合。二维相干光谱学最早是在核磁共振中发展起来的。在过去的十年中，在光谱的红外和光学区域实施二维光谱学方面取得了广泛的进展。首席研究小组在开发利用近红外光研究半导体中的电子跃迁的方法方面处于领先地位。最近，这些研究包括了大量的GaAs天然量子点和InAs自组装量子点。然而，到目前为止使用的方法，基于检测由样品的三阶非线性响应产生的光信号，不适合用于小的量子发射体集合，这将不会产生形成良好的信号光束。因此，这个项目使用了一种新的二维光谱学方法，通过测量光电流来检测四阶布居。这种方法将应用于InAs量子点和嵌入二极管结构的量子点分子。其目标是了解和测量量子点之间的相互作用，以促进对这些纳米系统中量子现象的基本理解。这种理解可以改进具有目标量子力学状态和动力学的系统的设计。

Non-technical abstractSemiconductor quantum dots have discrete energy levels similar to those in an atom, thus they are often described as as "artificial atoms". Unlike atoms, the energy level structure of a quantum dot can be engineered, making them attractive for a wide range of applications ranging from highly efficient lasers to quantum information processing. In addition, quantum dots can be embedded in solid-state devices, a key feature for use in applications. When quantum dots are brought into proximity to one another, their interaction results in new states, just as the interaction between atoms results in the formation of molecules. This project will employ a new coherent optical method to observe and characterize the interactions between quantum dots with sufficient spatial resolution to isolate a single dot or a small set of interacting dots. This new optical method is inspired by established magnetic resonance tachniques that are used to determine molecular structure. Furthermore, the spectroscopic technique developed by this project will have broader applications. For example, it could be used to study excitation processes in photovoltaic solar cells. This project will combine research and education by training students in the multidisciplinary field of coherent optical spectroscopy of solid state systems. This training will include the basic science of the interaction of condensed matter systems with light as well as practical aspects of photonics and microfabrication.Technical AbstractSemiconductor quantum dots grown by molecular beam epitaxy have possible applications ranging from low-threshold laser diodes to implementing qubits in quantum information science. Epitaxially grown quantum dots have been studied extensively using single dot techniques, however single dot techniques are not as good at probing the coupling between quantum dots. Interactions can dramatically alter the optical and electronic properties of quantum dots. Furthermore, quantum information schemes require that there be controllable interactions between qubits, and hence between quantum dots. This project probes the coupling between quantum dots using a new implementation of optical multi-dimensional coherent spectroscopy based on photocurrent readout and applying it to small ensembles of InGaAs quantum dots. Two-dimensional coherent spectroscopy was originally developed in nuclear magnetic resonance. Over the last decade, there has been extensive progress in implementing two-dimensional spectroscopy in the infrared and optical regions of the spectrum. The principal investigator's group is a leader in developing methods for using it to study electronic transitions in semiconductors using near-infrared light. Recently these studies have included large ensembles of GaAs natural quantum dots and InAs self-assembled quantum dots. However, the methods used so far, based on detecting an optical signal produced by the third-order nonlinear response of the sample, are not appropriate for use on small ensembles of quantum emitters, which will not generate a well formed signal beam. Thus this project uses a new approach to two-dimensional spectroscopy that detects a fourth-order population through measurement of photocurrent. This approach will be applied to InAs quantum dots and quantum dot molecules embedded in a diode structure. The goal is to understand and measure the interactions between quantum dots to advance the fundamental understanding of quantum phenomena in these nanoscale systems. This understanding can improve the design of systems with target quantum mechanical states and dynamics.