Electrical control of quantum dot spin qubits
Electrical control of quantum dot spin qubits
复制标题
量子点自旋量子位的电控制
DOI：
10.1140/epjd/e2010-00003-2
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
E. Laird
中科院分区：
文献类型：
--
作者：
E. Laird
本论文的实验是探索在四个量子点的装置中，电子自旋与电场的相互作用。这些实验特别受到利用电场控制自旋量子比特的前景的激励。第二章介绍了量子点中单自旋的超精细效应。核极化的波动允许单自旋共振由振荡电场驱动。自旋共振光谱揭示了通过驱动共振在量子点设备内部建立的核极化。两个耦合自旋的演化是由超精细相互作用和交换作用控制的，超精细相互作用倾向于导致自旋退相，交换作用倾向于阻止自旋退相。在第三章中，在具有可调交换的装置中研究了退相，探索了交换主导和超精细主导区域之间的交叉。与理论预测一致，观察到自旋转换几率的振荡和退相的饱和。第4章讨论了一个三点装置，它被认为是一种完全由交换控制的潜在量子比特。的量子位状态的准备和读出演示，连同任意操纵所需的两个相干交换操作之一。描述了一种允许快速器件测量的新读出技术。在第五章中，我们尝试用一个四点器件来制作一个两量子比特的门。虽然自旋量子位操作还不可能，但测量到的点对之间的静电相互作用原则上足以用于相干量子位耦合。III
This thesis presents experiments exploring the interactions of electron spins with electric fields in devices of up to four quantum dots. These experiments are particularly motivated by the prospect of using electric fields to control spin qubits. A novel hyperfine effect on a single spin in a quantum dot is presented in Chapter 2. Fluctuations of the nuclear polarization allow single-spin resonance to be driven by an oscillating electric field. Spin resonance spectroscopy revealed a nuclear polarization built up inside the quantum dot device by driving the resonance. The evolution of two coupled spins is controlled by the combination of hyperfine interaction, which tends to cause spin dephasing, and exchange, which tends to prevent it. In Chapter 3, dephasing is studied in a device with tunable exchange, probing the crossover between exchange-dominated and hyperfine-dominated regimes. In agreement with theoretical predictions, oscillations of the spin conversion probability and saturation of dephasing are observed. Chapter 4 deals with a three-dot device, suggested as a potential qubit controlled entirely by exchange. Preparation and readout of the qubit state are demonstrated, together with one out of two coherent exchange operations needed for arbitrary manipulations. A new readout technique allowing rapid device measurement is described. In Chapter 5, an attempt to make a two-qubit gate using a four-dot device is presented. Although spin qubit operation has not yet been possible, the electrostatic interaction between pairs of dots was measured to be sufficient in principle for coherent qubit coupling. iii
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