Long distance qubit-qubit coupling in silicon quantum dots

摘要：我研究了量子力学自旋与绝缘体之间的相互作用，这些自旋可控地捕获在半导体(如硅)和绝缘体界面上的称为量子点的小区域中。即使电子的电场是球形的，电子也是有取向的，即自旋。自旋可以对信息进行编码，这些信息可以借助电场和磁场进行控制。量子点中的电子自旋可以在所谓的稀释冰箱提供的寒冷环境中进行研究，稀释冰箱可以将量子点及其周围环境冷却到接近绝对零度。需要如此低的温度才能将这些微小颗粒发出的微弱信号与不可避免的嘈杂环境造成的信号区分开来。为了完全处理自旋中包含的信息，它们需要以明确定义的方式相互作用。我研究的是一种可以被视为两个事实相互作用的互动。首先，两个电子相互排斥，因为它们都有一个签名相同的电荷。其次，两个能量和取向完全相同的电子不可能占据完全相同的物理空间。在两个附近的电子被捕获的系统中，它们会重复地彼此交换自旋方向。这种效应称为交换相互作用。事实证明，在一个由三个或更多量子点电子组成的系统中，外层电子也可以通过自旋交换进行相互作用。我们的目标是应用这种效应来演示与量子点大小相比更长的距离上的量子比特-量子比特相互作用。特别是，我们的目标是研究由此产生的两量子比特门的可控性和质量。如果足够强大和可控，这种和相互作用将是实现可伸缩量子比特处理器的有益一步。

Abstract: I study the interaction between quantum mechanical spins controllably trapped in small regions known as quantum dots at the interfaces of a semiconductor, such as silicon, and and an insulator. Even though the electric field of an electron is spherical, electrons have orientation, the spin. Spins can encode information, which can be controlled with the help of electric and magnetic fields. Electron spins in quantum dots can be studied in cold environments provided by so-called dilution refrigerators, which cool them and their immediate environment down very close to absolute zero. Such cold temperatures are required to differentiate the faint signals transmitted by these tiny particles from the ones caused by inevitably noisy environment. To fully process the information contained in spins, they need to interact with one another in a well-defined manner. I study an interaction which can be seen as an interplay of two facts. First, two electrons repel each other due to both having a charge with the same signature. Second, two electrons with exactly the same energy and orientation cannot occupy exactly the same physical space. In systems where two nearby electrons are trapped, they repeatedly swap their spin orientations with one another. This effect is known as the exchange interaction. It turns out that the outer electrons in a system of three or more quantum dot electrons can also interact via spin exchange. We aim to apply this effect to demonstrate qubit-qubit interactions over distances that are long compared to quantum dot sizes. In particular, we aim to study the controllability and quality of the resulting two-qubit gates. If sufficiently strong and controllable, such and interaction would be a helpful step towards realising scalable qubit processors.