Electron Self-Organisation and Applications

电子自组织及其应用

• 批准号: EP/J013153/1
• 负责人: Michael Pepper
• 金额: $ 109.45万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FJ013153%2F1
• 关键词: Electron; Self; Organisation; Applications

In most situations electrons in semiconductors can be regarded as free with their energy determined by their total number and their effective mass with the mutual repulsion only slightly modifying this free electron picture. However at low values of carrier concentration the repulsion can dominate the manner in which the electrons diffuse in the solid, a voluminous amount of theory has shown that at sufficiently low temperatures the electrons can arrange themselves into a crystalline ensemble. This is termed a Wigner Crystal, or Wigner Lattice, after Wigner who first predicted such a phenomenon, it has proved rather difficult to observe as the observation of a regular structure is not simple and often the predictions of theory are not found due to the presence of disorder. In one dimension the electrons form a single line and the Wigner Crystal is the trivial case of the electrons seeking a regular periodicity. However, as the confinement weakens, or the electron repulsion increases, so it is possible for the line of electrons to distort as electrons attempt to maximise their separation. In the limit the row splits into two separate rows. The experimental system for such investigations is the electron gas in the GaAs-AlGaAs heterostructure grown by Molecular Beam Epitaxy and the samples are fabricated using high resolution electron beam lithography. In these samples it is possible to control the confinement potential by patterned gates to which voltages are applied, when the samples are sufficiently short electrons drift through ballistically which is without being scattered by random impurities or defects. In this regime the conductance of a one-dimensional wire takes a value 2e2/h where the factor of 2 arises from the spin degeneracy, e is the electron charge and h is Planck's constant. Consequently when a row of electrons splits into 2 rows a conductance of 4e2/h is observed as the ground state. By following the values of conductance as the confinement is changed so the movement of energy levels can be obtained as a function of confinement potential. This has been observed and we call the two rows formed as a result of the electron-electron repulsion the Incipient Wigner Lattice, IWL.Analysis of the results on the movement of energy levels has shown that prior to the formation of the two separate rows a hybridised state is formed in which two electrons are shared between the two rows such that they form a distorted single row. Quantum Mechanics dictates that two electrons shared in this way must have opposite spins and they can be entangled as a consequence of which they each "know" the quantum state the other is in. Entanglement is a remarkable phenomenon in which if the electrons are separated but still entangled then a change of state of one will produce a change in the state of the other. This remarkable property lies at the heart of many proposals for quantum information processing and quantum logic and may give rise to practical consequences not yet envisaged.In this research project we propose to study the IWL and optimise the creation of the hybrid state in which the electrons are entangled. Once this state is completely understood the properties of entangled electrons will be studied by injecting them from the IWL into other quantum structures which essentially form an early quantum integrated circuit. One of the characteristics of entangled electrons is that if two of them are in this state then a variation of the wavelength of them is effectively doubled compared to a single electron. Consequently if we perform an interference experiment there is an immediate difference between the behaviour of entangled and normal electrons, this is the effect which we will explore. The ultimate objective of the work is to develop a method of delivering a stream of entangled electrons and then demonstrate the entanglement in a series of integrated quantum devices with a view to their practical application

在大多数情况下，半导体中的电子可以被认为是自由电子，它们的能量由它们的总数和它们的有效质量决定，相互排斥只是稍微改变了这种自由电子图像。然而，在载流子浓度较低时，斥力可以支配电子在固体中扩散的方式，大量的理论表明，在足够低的温度下，电子可以自己排列成一个晶体系综。这被称为维格纳晶体或维格纳晶格，在维格纳第一次预测这种现象之后，它被证明是相当难以观察的，因为对规则结构的观察并不简单，而且由于无序的存在，经常无法发现理论的预测。在一维中，电子形成一条单线，而维格纳晶体是电子寻求规则周期性的平凡例子。然而，当约束减弱或电子斥力增加时，当电子试图最大限度地分离时，电子线就有可能扭曲。在极限情况下，该行分成两个单独的行。采用分子束外延生长的GaAs-AlGaAs异质结构中的电子气体作为实验系统，采用高分辨率电子束光刻技术制备样品。在这些样品中，可以通过施加电压的图形门来控制约束电位，当样品足够短时，电子以弹道方式漂移，而不会被随机杂质或缺陷散射。在这种情况下，一维导线的电导率为2e2/h，其中因子2来自自旋简并，e是电子电荷，h是普朗克常数。因此，当一排电子分成两排时，基态的电导为4e2/h。通过跟踪约束变化时的电导值，可以得到能级的运动作为约束势的函数。这已经被观察到，我们把由于电子-电子排斥而形成的两行称为早期维格纳晶格（IWL）。对能级运动结果的分析表明，在形成两个单独的行之前，形成了一个杂化状态，其中两个电子在两行之间共享，从而形成了一个扭曲的单行。量子力学表明，以这种方式共享的两个电子必须具有相反的自旋，并且它们可以纠缠在一起，因为它们每个人都“知道”对方所处的量子态。纠缠是一种引人注目的现象，如果两个电子分开了，但仍然纠缠在一起，那么一个电子的状态改变会引起另一个电子状态的变化。这一显著特性是量子信息处理和量子逻辑的许多建议的核心，并可能产生尚未设想的实际后果。在这个研究项目中，我们建议研究IWL并优化电子纠缠的杂化态的产生。一旦这种状态被完全理解，纠缠电子的性质将通过从IWL注入其他量子结构来研究，这些结构本质上形成了早期的量子集成电路。纠缠电子的特征之一是，如果其中两个电子处于这种状态，那么它们的波长变化实际上是单个电子的两倍。因此，如果我们进行干涉实验，在纠缠电子和正常电子的行为之间会有直接的区别，这就是我们将要探讨的效应。这项工作的最终目标是开发一种传输纠缠电子流的方法，然后在一系列集成量子器件中演示纠缠，以期其实际应用