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/S015728/1
• 负责人: Sanjeev Kumar
• 金额: $ 133.58万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2019
• 资助国家: 英国
• 起止时间: 2019 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=MR%2FS015728%2F1
• 关键词: Engineering; Future; Quantum; Technologies; Low

Classically electrons in a three-dimensional solid can change their momentum in all possible directions. However, electrons in semiconductors can be manipulated so that they are constrained to move in lower dimensions. One of the perfect examples of such a system is a semiconductor heterostructure of GaAs/AlGaAs forming a plane of electrons, only a few nanometer thick, at its junction where electrons possessing quantised energy and freedom to change momentum in the plane. Such remarkable ensemble of non-interacting electrons is known as the two-dimensional electron gas (2DEG). The electrons in a 2DEG system are highly mobile and at low temperatures their motion is mainly scattering free due to the reduction in the interaction with lattice vibrations (phonons) and there is little impurity scattering. When the 2D electrons are electrostatically squeezed to form a narrow, 1D channel whose effective size is less than the electron mean free path for scattering then quantum phenomena associated with the electrons becomes resolved. In this situation, the energy of 1D electrons becomes quantised and discrete levels are formed. At a low carrier concentration of electrons, if the potential which is confining the 1D electrons is relaxed then electrons can arrange themselves into a periodic zig- zag manner forming a Wigner Crystal, named after Wigner who first predicted such a phenomenon in metal in 1936. Recently the distortion of a line of electrons into a zig-zag and then into two separate rows of electrons was observed and associated rich spin and charge phases. A very subtle change in confinement can result in two rows emerging from a zig-zag state which indicates that there is a narrow range where wavefunctions separate and form entangled states. Entanglement is a remarkable phenomenon in which a change in state of one electron will introduce a change in state of another. This amazing property forms the basis for quantum information processing with practical consequences related to quantum technologies, which will be investigated in this proposal. Another most important aspect of my Fellowship proposal is investigating the zig-zag regime or relaxed 1D system in search of fractional quantum states in the absence of a magnetic field. In the presence of a large magnetic field the energy of a 2DEG is quantized to form Landau levels which gave rise to two celebrated discoveries of the Integer and fractional quantum Hall effects in 1980 and 1982 respectively. Such unexpected revelations then pose a question whether fractional quantised states in the absence of any magnetic field in any lattice or topological insulators could ever be observed? However, there were no reports of observations of any fractional states without a magnetic field until the recent discovery of fractional charges of e/2 and e/4 arising from the relaxed zig-zag state in a Germanium-based 1D system. The proposal is inspired by this and the recent experimental finding of non-magnetic self-organised fractional quantum states in tradition GaAs based 1D quantum wires, which was completely unanticipated. The research aim is to introduce new insights, and new aspects of quantum physics, by exploiting the interaction effects in low-dimensional semiconductors by manipulating electron wavefunctions in a controllable manner to allow technological exploitation of basic quantum physics. The major challenges to be investigated: spin and charge manipulation, demonstrating electron entanglement and detection, mapping self-organised fractional states and their spin states, controlled manipulation and detection of hybrid fractional states and establishing if they are entangled. This research proposal opens up a new area in the quantum physics of condensed matter with the generation of Non-Abelian fractions which can be used in a Topological Quantum Computation scheme.

传统上，三维固体中的电子可以在所有可能的方向上改变它们的动量。然而，半导体中的电子可以被操纵，从而限制它们在较低维度中移动。这种系统的完美例子之一是 GaAs/AlGaAs 的半导体异质结构，形成一个只有几纳米厚的电子平面，在其交界处，电子拥有量子化的能量和改变平面内动量的自由度。这种非相互作用电子的非凡集合被称为二维电子气（2DEG）。 2DEG 系统中的电子具有高度的移动性，并且在低温下，由于与晶格振动（声子）的相互作用减少，它们的运动主要是无散射的，并且几乎没有杂质散射。当 2D 电子被静电挤压形成一个狭窄的 1D 通道，其有效尺寸小于电子平均散射自由程时，与电子相关的量子现象就得到解决。在这种情况下，一维电子的能量被量子化并形成离散能级。在电子载流子浓度较低的情况下，如果限制一维电子的电势松弛，那么电子可以将自己排列成周期性的之字形，形成维格纳晶体，该晶体以维格纳命名，他于 1936 年首次预测了金属中的这种现象。最近，观察到一行电子扭曲成之字形，然后扭曲成两行独立的电子，并与丰富的自旋和电荷相相关。限制的非常微妙的变化可能会导致从之字形状态出现两行，这表明波函数分离并形成纠缠态的范围很窄。纠缠是一种显着的现象，其中一个电子状态的变化将引起另一个电子状态的变化。这一惊人的特性构成了量子信息处理的基础，并具有与量子技术相关的实际后果，本提案将对此进行研究。我的奖学金提案的另一个最重要的方面是研究锯齿形体系或松弛一维系统，以在没有磁场的情况下寻找分数量子态。在存在大磁场的情况下，2DEG 的能量被量子化以形成朗道能级，这分别导致了 1980 年和 1982 年整数量子霍尔效应和分数量子霍尔效应的两项著名发现。这种意想不到的发现提出了一个问题：在任何晶格或拓扑绝缘体中没有任何磁场的情况下，是否可以观察到分数量子态？然而，直到最近发现基于锗的一维系统中松弛之字形态产生的 e/2 和 e/4 分数电荷之前，还没有在没有磁场的情况下观测到任何分数态的报道。该提案的灵感来自于这一点以及最近在传统 GaAs 基一维量子线中非磁性自组织分数量子态的实验发现，这是完全出乎意料的。研究目的是通过以可控方式操纵电子波函数来利用低维半导体中的相互作用效应，从而引入量子物理的新见解和新方面，从而实现基础量子物理的技术开发。要研究的主要挑战：自旋和电荷操纵、演示电子纠缠和检测、绘制自组织分数态及其自旋态、混合分数态的受控操纵和检测以及确定它们是否纠缠。这项研究提案通过生成可用于拓扑量子计算方案的非阿贝尔分数，开辟了凝聚态量子物理的新领域。

项目成果

Resistance hysteresis in the integer and fractional quantum Hall regime

整数和分数量子霍尔体系中的电阻滞后

• DOI: 10.1103/physrevb.107.205307
• 发表时间: 2023
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Peraticos E

Nonequilibrium phenomena in bilayer electron systems

双层电子系统中的非平衡现象

• DOI: 10.1103/physrevb.107.l041302
• 发表时间: 2023
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Shevyrin A

Interactions and non-magnetic fractional quantization in one-dimension.

• DOI: 10.1063/5.0061921
• 发表时间: 2021-09-13
• 期刊: Applied physics letters
• 影响因子: 4
• 作者: Kumar S;Pepper M
• 通讯作者: Pepper M

Hall resistance anomalies in the integer and fractional quantum Hall regime

• DOI: 10.1103/physrevb.102.115306
• 发表时间: 2020-09
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: E. Peraticos;Sanjeev Kumar;M. Pepper;A. Siddiki;I. Farrer;D. Ritchie;G. Jones;J. Griffiths

Engineering electron wavefunctions in asymmetrically confined quasi one-dimensional structures

非对称约束准一维结构中的工程电子波函数

• DOI: 10.1063/5.0045702
• 发表时间: 2021
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Kumar S