Real-Time Electron Dynamics in Nanoscale Structures

纳米尺度的电结构表现出许多有趣的现象，如库仑阻塞或量子相干。 这种现象传统上一直使用直流或准直流测量技术进行研究，即使基本的电子动力学发生在更短的时间尺度上。 虽然这样的测量提供了大量的信息，但通过研究单个电子的动力学可以获得更多的信息。 例如，电子隧穿中的时间相关性预计在通过库仑阻塞纳米结构的传输中，但从未被直接观察到。 这个个人研究者奖支持一个项目，通过使用射频单电子晶体管来研究量子点中单个电子的运动来解决这些问题。 这样做最终将允许在数十到数百纳秒的时间尺度上研究电子相关性和量子相干性。 将对单量子点和双量子点进行一系列实验，目的是通过它们的计数统计来研究电子关联，并在它们的内在时间尺度上探测量子相干现象。 这些实验中使用的技术也与量子计算中的量子比特读出问题有关，并有望在一般情况下阐明量子测量问题。 这项工作涉及使用纳米纤维和射频表征的尖端技术，以及低温和低噪声技术，为参与的学生提供在学术界或工业界有价值的技能。对于许多纳米结构（其物理尺寸以十亿分之一米测量），单个电子的运动在其电气特性中起着重要作用。 虽然单个电子的作用以及它们之间的相互作用早已被认识到，但纳米结构中的电输运通常通过测量平均电导来探测。 虽然这样的测量提供了大量的信息，但通过研究单个电子的动力学可以获得更多的信息。 该个人研究者奖支持一个项目，该项目通过使用快速且非常灵敏的静电计（称为射频单电子晶体管）来研究半导体量子点上单个电子的运动来解决这些问题。 例如，通过观察单个电子在驱动通过点的电流中的运动，将有可能提取关于电子如何在纳米结构中相互作用的额外信息。 由于电子是量子力学物体，研究还将集中在观察电子运动的过程如何影响运动本身。 这个问题对于量子计算中量子比特的测量也很重要，它涉及到量子力学物体在受到宏观物体影响时如何失去其波动性质（量子相干性）的问题。 在短时间尺度（百万分之一秒或更短）上测量单个电子的能力应该为这些问题提供新的线索。这项工作涉及使用纳米纤维和射频表征的尖端技术，以及低温和低噪声技术，为学生提供在学术界或工业界有价值的技能。

Nanoscale electrical structures exhibit numerous interesting phenomena such as the Coulomb blockade or quantum coherence. Such phenomena have traditionally been studied using dc or quasi-dc measurement techniques, even though the underlying electron dynamics take place on much shorter time scales. While such measurements provide a tremendous amount of information, much more could be accessed by studying the dynamics of individual electrons. For instance, temporal correlations in electron tunneling are expected in transport through Coulomb blockade nanostructures, but have never been observed directly. This Individual Investigator Award supports a project that addresses such issues by using a radio-frequency single-electron transistor to study the motion of individual electrons in a quantum dot. Doing so will ultimately allow investigation of electronic correlations and quantum coherence on time scales of tens to hundreds of nanoseconds. A series of experiments on both single and double quantum dots will be undertaken, with the goal of studying electron correlations by means of their counting statistics and probing quantum coherent phenomena on their intrinsic time scales. The techniques used in these experiments are also relevant to the qubit readout problem in quantum computation, and are expected to shed light on the quantum measurement problem in general. This effort involves use of cutting-edge techniques in nanofabrication and radio-frequency characterization, as well as cryogenic and low noise techniques, providing the students involved with skills valuable in either academia or industry.For many nanoscale structures (whose physical dimensions are measured in billionths of a meter), the motion of individual electrons plays an important role in their electrical characteristics. While the roles of individual electrons and the interactions between them have long been recognized, electrical transport in nanostructures is usually probed by measuring the average conductance. Although such measurements have provided a tremendous amount of information, much more could be accessed by studying the dynamics of individual electrons. This Individual Investigator Award supports a project that addresses such issues by using a fast and very sensitive electrometer known as a radio-frequency single electron transistor to study the motion of individual electrons on a semiconductor quantum dot. By observing the motion of individual electrons in a current driven through the dot, for instance, it will be possible to extract additional information about how electrons interact in nanostructures. Because electrons are quantum-mechanical objects, the research will also focus on how the process of observing the electron motion affects the motion itself. This problem, which is also important for measurement of a qubit in quantum computation, is related to the question of how quantum mechanical objects lose their wave-like properties (their quantum coherence) when affected by a macroscopic object. The ability to measure individual electrons on short time scales (millionths of a second or less) should shed new light on such issues. This effort involves use of cutting-edge techniques in nanofabrication and radio-frequency characterization, as well as cryogenic and low noise techniques, providing the students involved with skills valuable in either academia or industry.