Nanoelectronic Based Quantum Physics- Technology and Applications.

流过半导体器件的电子在现代生活中具有极其重要的意义。当器件做得足够小，以至于其中一个尺寸是纳米级时，电子的量子性质就会脱颖而出，必须详细考虑。在非常低的温度下工作减少了电子-电子的相互散射，并导致电子传递的波动性质在可以超过设备尺寸的距离上变得可观察到。使用比波函数的相干长度或杂质散射事件之间的距离更小的设备进行实验，可以观察到一系列量子效应。近年来，理论提出“量子计算机”比传统计算机具有一定的优势，因为它们允许大规模并行操作模式。这是基于量子原理的，因此，如果两个电子处于量子态，那么它们的总自旋波函数反映了可能存在的状态范围。正是这种状态的叠加是量子计算机的基础。它是一种纯粹的量子现象，并产生了诸如“薛定谔的猫”之类的概念，这些概念例证了量子力学的非直觉性质。另一个可能带来新技术应用的特性是显著的纠缠。这种纯粹的量子效应导致两个电子处于相同的量子态，并且“知道”彼此的存在，因此，如果一个的自旋被旋转，那么另一个的自旋就会受到影响，尽管它们之间有相当大的距离。在这项工作中，我们建议利用半导体纳米结构来发现新的量子效应，并将它们结合起来创建用于实际开发的集成量子电路。该项目在三个不同的中心整合了理论、半导体生长/制造和测量，它的初始目标是设计和制造关键的量子元件，以便后续集成。一个主要组成部分是量子泵，它可以以非常高的精度在高频上传输受控数量的电子。该装置可用于产生纠缠电子，然后对纠缠电子进行研究并投入使用。另一个重要的组成部分是光学中偏振光分束器的电子类比，这里通过使用局部电子自旋，根据其自旋方向，进入的电子要么被传输，要么被反射。我们还建议利用自旋-轨道耦合，允许自旋极化电流在纳米结构中建立，然后可以用于量子器件。进一步提出利用间接电子相互作用机制在不同器件之间传递自旋信息。在这方面可能具有新特性的系统是早期的维格纳晶格，当电子线受到弱约束并且电子-电子排斥的最小化迫使电子形成两行时，它可以形成。在这里，它们可以纠缠在一起，并以一种与泵互补的方式构成纠缠电子的连续供应。新型量子元件将得到开发。然后，它们将被整合成一种早期的电路，在这种电路中，量子效应主导着电路的特性。它旨在开发基本的量子处理器，特别是CNOT门，其中一个电子的自旋取决于另一个电子的自旋方向。除了这些目标之外，一些附带成果将对其他领域产生影响。例如，有必要开发在超低温（1毫开尔文）下测量电子特性的技术，并且要开发的自旋极化电流将在自旋电子学的重要领域中得到应用。

Electrons flowing through semiconductor devices are of immense importance in modern life. When devices are made sufficiently small, such that one of the dimensions is in the nanometre regime, the quantum nature of the electron comes to the fore and must be considered in detail. Working at very low temperatures reduces the mutual electron-electron scattering and results in the wave nature of electron transport becoming observable over distances which can exceed the size of the device. Experiments using devices which are smaller than the coherence length of the wavefunction, or the distance between impurity scattering events, have allowed observation of a range of quantum effects.In recent years theories have proposed that a "quantum computer" has certain advantages over conventional computers as they allow a massively parallel mode of operation. This is based on quantum principles, thus if two electrons are in a quantum state then their total spin wavefunction reflects the range of possible states that can be present. It is this superposition of states which is the basis of a quantum computer. It is a purely quantum phenomenon and has given rise to concepts such as "Schrodinger's Cat" which exemplify the non-intuitive nature of quantum mechanics. Another property which could give rise to new technological applications is the remarkable entanglement. This purely quantum effect results in two electrons being in the same quantum state and "knowing" about each other's existence, consequently if the spin of one is rotated then the spin of the other is affected despite there being a considerable distance between them.In this work we propose to utilise semiconductor nanostructures to find new quantum effects and combine them to create integrated quantum circuits for practical exploitation. The project integrates theory, semiconductor growth/fabrication and measurements in three different centres, it has as initial targets the design and fabrication of key quantum components forsubsequent integration. A principal component is the Quantum Pump which can transmit controlled numbers of electrons at high frequencies with very high accuracy. This device can be used for the generation of entangled electrons which can then be investigated and put to use. Another component which is of importance is the electronic analogy of the polarising beam splitter in optics, here by using localised electron spins an incoming electron is either transmitted or reflected depending on its spin direction. We also propose to exploit the spin-orbit coupling which allows a spin polarised current to be established in a nanostructure which can then be utilised in a quantum device.It is further proposed to build on the use of an indirect electron interaction mechanism to transmit spin information between different devices. A system which may have novel properties in this regard is the incipient Wigner lattice which can form when a line of electrons is weakly confined and minimisation of the electron-electron repulsion forces the electrons to form two separate rows. Here they can be entangled and constitute a continuous supply of entangled electrons in a manner which is complementary to the pump.New types of quantum components will be developed. They will then be integrated to form an early type of circuit in which quantum effects dominate the properties. It is intended to develop basic quantum processors in particular a CNOT gate in which the spin of an electron is rotated depending on the direction of the spin of another. In addition to these objectives a number of spin-off achievements will have an impact on other fields. For example it will be necessary to develop techniques of measurement of electronic properties at ultra low temperatures, 1 milliKelvin, and the spin polarised currents to be developed will have applications in the important field of spintronics.