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Exchange fields and relaxation times in quantum dot

量子点中的交换场和弛豫时间

基本信息

批准号：
263334920
负责人：
Professor Dr. Herbert Schoeller
金额：
--
依托单位：
PGI-2 / IAS-3: Theoretische Nanoelektronik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/263334920?language=en
关键词：
Exchange fields relaxation times quantum

项目摘要

The goal of the proposed project is to give a theoretical description of (A) time-dependent decay in multiple quantum-dot setups, and (B) spintronic exchange effects in quantum-dot spin valves, both of which are important problems characterizing the response of nanoelectronic systems to external control and driving.In subproject (A), we will calculate the decay modes of composite quantum-dot systems driven out of equilibrium, and determine how the current through one constituent quantum dot can be used to measure the decay modes of the others. This understanding of the time-dependent response is of key importance to physical and technological applications of externally driven quantum-dot devices, e.g., in sensitive electron-counting and qubit readout, respectively. We will establish measurement setups and protocols accounting for the effects of quantum-fluctuations. In particular, we will study how one can measure the recently predicted fermion-parity decay mode of a quantum dot, which is strikingly insensitive to Coulomb interaction and other local effects due to a fundamental superselection rule of quantum mechanics.In subproject (B), we will calculate the transport through a quantum dot coupled to biased noncollinear ferromagnets, accounting for the competition of the exchange field induced by spin-dependent confinement and the exchange field induced by tunneling and Coulomb interaction. These mechanisms are fundamental to the quest for time-dependent control over single spins in nanostructures for spintronics and quantum information. We will make predictions for stationary as well as time-dependent measurements that aim to detect and disentangle these two effects. In particular, we will predict how the exchange fields develop in time after switching on the tunneling between the quantum dot and the noncollinear ferromagnets.For both problems we will apply a causal superfermion formulation of the real-time diagrammatic technique. This approach reveals novel fundamental aspects of nonequilibrium processes and allows us to obtain the time-evolution of the reduced density operator of the quantum dot in a more efficient way, complementary to the physically more transparent quantum-kinetic equations for coupled observables.A feature central to both proposed subprojects is that we can systematically treat -- within a single approach - higher-order perturbations to the complementary limits of arbitrary interaction and weak tunneling, and, on the other hand, arbitrary tunneling and weak interaction. In general, the approach simplifies many of the required calculations. It has already led to new exact results for strongly interacting quantum dots, e.g., establishing the fermion-parity decay mode, and it shows great potential for successfully realizing the proposed research program. Each proposed subproject involves an external researcher who brings in expertise on modeling devices in close collaboration with leading experimental efforts.

该项目的目标是对（A）多个量子点设置中的时间相关衰变和（B）量子点自旋阀中的自旋电子交换效应进行理论描述，这两个问题都是表征纳米电子系统对外部控制和驱动的响应的重要问题。在子项目（A）中，我们将计算复合量子点系统失去平衡的衰变模式，并确定当前如何通过一个组成量子点可以用来测量其他量子点的衰变模式。这种对时间相关响应的理解对于外部驱动的量子点器件的物理和技术应用至关重要，例如分别在敏感电子计数和量子位读出中。我们将建立测量装置和协议来解释量子涨落的影响。特别是，我们将研究如何测量最近预测的量子点的费米子宇称衰变模式，由于量子力学的基本超选择规则，该模式对库仑相互作用和其他局部效应极其不敏感。在子项目（B）中，我们将计算通过耦合到偏置非共线铁磁体的量子点的输运，考虑由自旋相关的限制以及隧道效应和库仑相互作用引起的交换场。这些机制对于寻求自旋电子学和量子信息纳米结构中单自旋的时间相关控制至关重要。我们将对静态和随时间变化的测量进行预测，旨在检测和消除这两种效应。特别是，我们将预测在量子点和非共线铁磁体之间打开隧道后交换场如何及时发展。对于这两个问题，我们将应用实时图解技术的因果超费米子公式。这种方法揭示了非平衡过程的新颖的基本方面，并使我们能够以更有效的方式获得量子点的降低密度算子的时间演化，与物理上更透明的耦合可观测量量子动力学方程互补。这两个拟议子项目的一个核心特征是，我们可以在单一方法中系统地处理对互补极限的高阶扰动。任意相互作用和弱隧道效应，另一方面，任意隧道效应和弱相互作用。一般来说，该方法简化了许多所需的计算。它已经为强相互作用量子点带来了新的精确结果，例如建立了费米子宇称衰变模式，并且它显示了成功实现所提出的研究计划的巨大潜力。每个拟议的子项目都涉及一名外部研究人员，他们与领先的实验工作密切合作，带来建模设备方面的专业知识。