Quantum mechanical simulation of superconducting qubits

量子计算机(QC)对我们生活的许多领域产生了巨大的影响，因此，它们不仅是学术界研究最多的话题之一，也是工业界研究最多的话题之一。霍尼韦尔、IBM和谷歌等公司正在使用不同的技术来创造量子比特。最有前途的技术之一是由约瑟夫森结(JJ)制成的超导量子比特。JJ用于超导材料，例如铝和由薄层非超导材料制成的隧道结，例如AlOx(在理想情况下x=1.5)。虽然量子比特的电路设计、纠错、重复性和可靠性都在不断改进，但在相关材料科学方面仍存在着重大的知识差距。例如，AlOx在Al上的生长过程并不清楚，这对于能够制备均匀、没有缺陷和表面粗糙度Jj的AlOx来说是至关重要的。JJ的任何缺陷，例如捕获在氧化物中的电荷、悬挂键和AlOx中不同的化学计量比(x可以是1.3到1.8之间的数字)，都会产生不同的隧道电流，从而产生不同的量子比特行为。量子比特行为的可变性使得电路的设计变得更加困难，增加了测量中的误差，减少了相干时间。这个项目的主要目标是开发一个独特的计算框架，能够模拟真实大小的超导量子比特。在这里，我们将把Al/AlOx/Al界面(约瑟夫森结)作为量子比特来研究。该模拟框架将结合各种量子力学方法，不仅可以模拟Al/AlOx/Al界面的材料生长，还可以模拟由于陷阱电荷和缺陷引起的隧道电流的变化。这种计算框架是最经济有效和节省时间的方法，以显著提高超导量子比特的可靠性、重复性和降低可变性。这项工作是基于与该领域的领先专家马丁·韦德斯教授小组的密切合作。我们的目标是模拟不同的架构和设备类型，以便评估和预测制造过程中的关键设计参数。理想的候选人将具有良好的计算技能和工程、物理或化学背景。了解计算方法，如密度泛函理论(DFT)和数值方法，是非常有利的，但不是强制性的。编程技能不是必需的，但将是有益的。此外，应聘者必须自我激励，对进行跨学科的计算和理论研究感兴趣，并具有良好的人际交往能力。该学生将成为格拉斯哥大学器件建模小组的成员，该小组可能是全球学术界最大的专业半导体器件小组的成员。该组织在包括不同来源的统计可变性的先进CMOS器件的3D模拟方面处于世界领先地位。根据EPSRC在信息和通信技术方案概况(2008)文件中的资助，该集团被列为五个主要的电子材料和设备中心之一。

Quantum computers (QC) have an enormous impact on many areas of our life and for this reason they are one of the most heavily researched topics not only in academia but also in the industry. Companies such as Honeywell, IBM and Google are using different technologies to create qubits.One of the most promising technology is superconducting qubits made from Josephson Junctions (JJ). JJ are made for a superconducting material, e.g. Al and tunnel junctions made from a thin layer of non-superconducting materials, e.g. AlOx (in an ideal case x=1.5). While there is constant improvement of the circuit designs, error corrections, reproducibility and reliability of the qubits, there is still significant knowledge gap in relevant material science. For example, the growth process of AlOx on top of Al is not well understood which is crucial to be able to fabricate uniform, without defects and surface roughness JJ. Any imperfections of the JJ, such as charges trapped in the oxide, dangling bonds and different stoichiometry in AlOx (x can be a number between 1.3 and 1.8) will produce different tunnelling current and hence different qubit behaviour. The variability of the qubit's behaviour makes the design of the circuit much harder and increases the errors in the measurements and decreases the coherent times.The main aim of this project is to develop a unique computational framework which will be able to simulate realistic size superconducting qubits. Here we will investigate Al/AlOx/Al interfaces (Josephson Junctions) as qubits. The simulation framework will combine various quantum mechanical methods which will allow us to simulate not only materials growth of Al/AlOx/Al interfaces but also the variability of the tunnelling current due to trap charges and defects. Such computational framework is the most cost effective and time saving approach in order to significantly improve the reliability, reproducibility and decrease variability in superconducting qubits.This work is based on close collaboration with the group of Prof Martin Weides, the leading expert in the field. The vision is to simulate various architectures and types of devices in order to evaluate and to predict the critical design parameters for the fabrication process.The ideal candidate will have good computational skills and a background in engineering, physics or chemistry. Knowledge of computational methods, such as Density Functional Theory (DFT) and numerical methods, is highly advantageous but not mandatory. Programming skills are not required but will be beneficial. Also, the candidate must be self-motivated, interested in conducting interdisciplinary computational and theoretical research and to have good interpersonal skills.The student will be part of the Device Modelling Group in the University of Glasgow, which is perhaps the largest specialised semiconductor device group in academia worldwide. The group is the world leader in 3D simulations of advanced CMOS devices that include different sources of statistical variability. The group is listed among the five leading Electronic Materials and Devices Centres according to EPSRC funding in the ICT Programme Landscape (2008) documents.