Open quantum dynamics of spin qubits on graphene nanoribbons

石墨烯纳米带上自旋量子位的开放量子动力学

• 批准号: 2744947
• 金额: --
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2744947
• 关键词: Open; quantum; dynamics; spin; qubits

The next generation of quantum computers will need to make use of new materials to realise higher temperature operation and all-electrical control of qubits. Strong contenders for achieving these goals are atomically precise graphene nanoribbons, whose true potential has only recently been uncovered with ground-breaking developments in nanofabrication. Due to their molecular precision, these auspicious graphene nanoribbons boast spin relaxation times on the order of milliseconds at temperatures as large as 10 K [1], offering exciting prospects for further investigations. This project will investigate a spin-qubit framework that exploits proximity effects to enable ultra-fast all-electrical single-qubit control with Rabi frequencies breaking the GHz barrier [2]. The overall aim is to understand the effects of spin-phonon coupling upon qubit stability by using a combination of theoretical and numerical methods. The ability to identify and characterise the spin decoherence channels will provide a stepping stone to understand the resilience of spin-qubit encoding strategies in graphene nanoribbons. The main objectives are to determine the effects of electron-phonon coupling and common random sources of elastic scattering upon qubit stability and model the open quantum dynamics of proximitised graphene nanoribbons(GNRs). Benefiting from the team's expertise, we will use many-body perturbation theory and numerically exact methods to obtain a robust microscopic theory applicable to realistic systems. The following effects will be considered. (i) Spin-phonon coupling. Electron-phonon coupling is the main charge relaxation mechanism in gate-defined graphene quantum dots [3] and is likely to be the main factor in setting the spin coherence time in bottom-up GNRs as evidenced by pulse electron paramagnetic resonance experiments [4]. (ii) Disorder. The most common imperfection in bottom-up GNRs are "bite defects" (i.e. missing C rings) at the edge [5]. We shall map out the open dephasing channels for (i) and (ii), calculating the microscopic relaxation times and the ensuing T1 and T2 times. The secondary objectives are: (1) characterise spin-phonon relaxation processes due to spin-orbit admixture; and (2) determine the impact of magnetic noise.

下一代量子计算机将需要利用新材料来实现更高温度的运行和量子位的全电控制。实现这些目标的强有力的竞争者是原子级精确的石墨烯纳米带，其真正的潜力直到最近才随着纳米制造领域的突破性发展而被发现。由于其分子精度，这些吉祥的石墨烯纳米带在高达 10 K 的温度下具有毫秒级的自旋弛豫时间 [1]，为进一步研究提供了令人兴奋的前景。该项目将研究一种自旋量子位框架，该框架利用邻近效应实现超快速全电单量子位控制，拉比频率突破 GHz 屏障 [2]。总体目标是通过结合理论和数值方法来了解自旋声子耦合对量子位稳定性的影响。识别和表征自旋退相干通道的能力将为理解石墨烯纳米带中自旋量子位编码策略的弹性提供基础。主要目标是确定电子声子耦合和常见的弹性散射随机源对量子位稳定性的影响，并对邻近石墨烯纳米带（GNR）的开放量子动力学进行建模。受益于团队的专业知识，我们将使用多体微扰理论和数值精确方法来获得适用于现实系统的稳健的微观理论。将考虑以下影响。 (i) 自旋声子耦合。电子-声子耦合是栅极定义的石墨烯量子点中的主要电荷弛豫机制[3]，并且可能是设置自下而上的GNR中自旋相干时间的主要因素，脉冲电子顺磁共振实验证明了这一点[4] 。 (二) 混乱。自下而上的 GNR 中最常见的缺陷是边缘处的“咬合缺陷”（即缺少 C 环）[5]。我们将绘制 (i) 和 (ii) 的开放相移通道，计算微观弛豫时间以及随后的 T1 和 T2 时间。次要目标是：（1）表征由于自旋轨道混合引起的自旋声子弛豫过程； (2)确定磁噪声的影响。