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.

经典地说，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，以便它们被限制在较低的维度上移动。这种系统的一个完美的例子是半导体异质结的GaAs/AlGaAs，在其结合处形成了一个只有几纳米厚的电子平面，其中的电子具有量化的能量和在平面上改变动量的自由。这种不相互作用的电子集合被称为二维电子气(2DEG)。二维EG系统中的电子具有很高的迁移率，在低温下，由于与晶格振动(声子)相互作用的减弱，电子的运动主要是自由散射，几乎没有杂质散射。当2D电子被静电压缩，形成一个有效尺寸小于电子平均散射自由程的一维窄通道时，与电子相关的量子现象就被解决了。在这种情况下，一维电子的能量被量子化，并形成离散能级。在电子的低载流子浓度下，如果限制一维电子的势能松弛，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，维格纳晶体是以维格纳的名字命名的，维格纳于1936年首次在金属中预测了这种现象。最近，观察到一条电子线扭曲成之字形，然后变成两行分开的电子，并伴随着丰富的自旋和电荷相。限制的一个非常细微的变化可以导致两行从Z字形状态出现，这表明存在一个狭窄的范围，其中波函数分离并形成纠缠态。纠缠是一种显著的现象，其中一个电子的状态改变会导致另一个电子的状态改变。这一惊人的性质构成了量子信息处理的基础，具有与量子技术相关的实际后果，这将在本提案中进行研究。我的奖学金提案的另一个最重要的方面是研究之字形制度或松弛的一维系统，以寻找在没有磁场的情况下的分数量子态。在强磁场的作用下，2DEG的能量被量子化，形成朗道能级，从而分别在1980年和1982年发现了整数量子霍尔效应和分数量子霍尔效应。这样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，是否能观察到分数量子态？然而，直到最近发现e/2和e/4的分数电荷产生于一个基于Ge的一维系统中的松弛之字态，还没有关于在没有磁场的情况下观察到任何分数态的报道。这一提议的灵感来自于这一点和最近的实验发现，即传统的基于GaAs的一维量子线中的非磁性自组织分数量子态，这完全是意想不到的。这项研究的目的是通过以可控的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，从而允许对基础量子物理的技术开发，从而引入量子物理的新见解和新方面。需要研究的主要挑战是：自旋和电荷操纵，演示电子纠缠和检测，映射自组织分数态及其自旋态，混合分数态的受控操纵和检测，以及确定它们是否存在纠缠。这一研究方案通过产生可用于拓扑量子计算方案的非阿贝尔分式，开辟了凝聚态物质量子物理的新领域。

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

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

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

Formation of a non-magnetic, odd-denominator fractional quantized conductance in a quasi-one-dimensional electron system

在准一维电子系统中形成非磁性奇分母分数量化电导

• DOI: 10.1063/1.5121147
• 发表时间: 2019
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Kumar S