Engineering Future Quantum Technologies in Low-Dimensional Systems

低维系统中的未来量子技术工程

• 批准号: MR/X006077/1
• 负责人: Sanjeev Kumar
• 金额: $ 75.82万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=MR%2FX006077%2F1
• 关键词: Engineering; Future; Quantum; Technologies; Low

Quantum transport in low-dimensional semiconductor nanostructures is a well-established field of research that has resulted in several landmark discoveries in solid-state physics over the past several decades. Among various findings, the one which stands out is the discovery of the Quantum Hall Effect (QHE) in 1980. The QHE was the first experimental demonstration of the quantum nature of the celebrated classical Hall effect. In the QHE, the transverse conductance of a two-dimensional electron gas is represented as (e^2/h).v, where v is the filling factor. The conductance shows remarkably flat plateaus for integer values of the filling factor. It may be noted that the transverse conductance or QHE is proportional to fundamental constants (e^2/h), and does not depend on the sample geometry or size, so is invariant. A pioneering theorist, R Laughlin proposed a theory describing the integer states in terms of a topological invariant, Chern number. In 1982, physicists working at Bell labs reported in the QHE measurements that new quantised plateaus appeared at fractional values of the filling factor, like 1/3. This remarkable discovery gave birth to the Fractional Quantum Hall Effect (FQHE). The observation was due to electron-electron interactions in the two-dimensional electron gas in high-quality semiconductors under the influence of a strong quantising magnetic field. FQHE was the first demonstration in solid state physics that the quasiparticles formed at the extremely high magnetic field and very low temperatures would possess a fraction of an electronic charge, say, 1/3. Following the discovery of the FQHE, several experimental studies resulted in the discovery of more than 100 new fractional states. While FQHE/QHE was receiving considerable attention in the 80s, an exciting development took shape when Haldane in 1988 proposed the idea of QHE without any magnetic field using the tight-binding model on a honeycomb lattice. He suggested that the existence of quantum Hall states do not necessarily require an external magnetic field, but depends on the symmetries of the system and its topological phases. This important contribution to the knowledge led to various discoveries, including the anomalous and Hall effects and topological insulators. It was shown in 1988 that conductance through a one-dimensional channel was quantised as (2e^2/h). N, where N is an integer. This was a remarkable observation and one of the significant discoveries in solid-state physics, that the conductance of 2D electrons, when confined to one dimension would quantise in units of fundamental constants (2e^2/h), a behaviour similar to the QHE although without any magnetic field. As FQHE was complementing the IQHE when electron-electron interactions were introduced, physicists wondered if there could be a fractional counterpart of the 1D integer conductance quantisation. This critical question in experimental physics remained unanswered until 2018/2019, when electrons in high-quality semiconductors based on GaAs showed fractional conductance quantisation in units of e^2/h at values 2/5,1/6, 1/2, etc. These new quantum states form when electrons in a 1D channel configure into a zigzag, enabling "ring paths" and "cyclic currents". These complex quantum phenomena result in fractional excitations which show promise for topological quantum computing schemes. This proposal aims to investigate the fractional quantum states formed in weakly confined 1D quantum wires, where several parameters play a significant role in achieving this unexpected quantum behaviour. We aim to investigate the nature of these new fractional quantum states and how their spin and charge phases could be measured and manipulated. These novel quantum states would be utilised to investigate entanglement via Aharonov-Bohn interferometry, spin blockage phenomena, fractional state selection via electron focusing, electronic charge via quantum shot noise measurements, etc.

低维半导体纳米结构中的量子输运是一个成熟的研究领域，在过去的几十年里在固态物理学领域取得了多项里程碑式的发现。在众多发现中，最引人注目的是 1980 年发现的量子霍尔效应 (QHE)。QHE 是对著名的经典霍尔效应的量子性质的首次实验演示。在QHE中，二维电子气的横向电导表示为(e^2/h).v，其中v是填充因子。对于填充因子的整数值，电导显示出非常平坦的平台。值得注意的是，横向电导或 QHE 与基本常数 (e^2/h) 成正比，并且不依赖于样本几何形状或大小，因此是不变的。作为一位先驱理论家，R Laughlin 提出了一种用拓扑不变量陈数来描述整数态的理论。 1982 年，贝尔实验室的物理学家在 QHE 测量中报告称，新的量子化平台出现在填充因子的小数值处，例如 1/3。这一非凡的发现催生了分数量子霍尔效应（FQHE）。这一观察结果是由于在强量子化磁场的影响下，高质量半导体中的二维电子气中的电子-电子相互作用。 FQHE 是固态物理学中首次证明，在极高磁场和极低温度下形成的准粒子将拥有一小部分电子电荷，例如 1/3。随着 FQHE 的发现，多项实验研究发现了 100 多个新的分数态。虽然 FQHE/QHE 在 80 年代受到了相当多的关注，但当 Haldane 在 1988 年提出使用蜂窝晶格上的紧束缚模型在没有任何磁场的情况下 QHE 的想法时，一个令人兴奋的发展开始形成。他提出，量子霍尔态的存在并不一定需要外部磁场，而是取决于系统的对称性及其拓扑相。这一对知识的重要贡献导致了各种发现，包括反常效应和霍尔效应以及拓扑绝缘体。 1988 年表明，通过一维通道的电导被量化为 (2e^2/h)。 N，其中N是整数。这是一项了不起的观察，也是固态物理学中的重大发现之一，即二维电子的电导，当局限于一维时，将以基本常数 (2e^2/h) 为单位进行量子化，这种行为类似于 QHE尽管没有任何磁场。当引入电子-电子相互作用时，FQHE 是对 IQHE 的补充，物理学家想知道是否可能存在一维整数电导量子化的分数对应物。实验物理学中的这个关键问题直到 2018/2019 年才得到解答，当时基于 GaAs 的高质量半导体中的电子在值 2/5、1/6、1/2 等处显示出以 e^2/h 为单位的分数电导量子化当一维通道中的电子配置成锯齿状时，这些新的量子态就会形成，从而实现“环形路径”和“循环电流”。这些复杂的量子现象会产生分数激发，这为拓扑量子计算方案带来了希望。该提案旨在研究弱约束一维量子线中形成的分数量子态，其中几个参数在实现这种意想不到的量子行为中发挥着重要作用。我们的目标是研究这些新的分数量子态的性质以及如何测量和操纵它们的自旋和电荷相位。这些新颖的量子态将用于通过阿哈罗诺夫-博恩干涉测量法研究纠缠、自旋阻塞现象、通过电子聚焦的分数态选择、通过量子散粒噪声测量的电子电荷等。