Control characterisation of noisy quantum devices

目前的项目将通过广泛的数值计算和一种新的控制范例来表征受控量子设备在存在噪声的情况下的性能。这对于新兴的量子技术来说很重要，因为噪声是一个主要障碍。该项目的目标是对在嘈杂的单量子比特和两个量子比特实验中可以实现的操作进行数值表征，开发估计技术和更好的噪声控制，以及一个更简单的分析工具箱来描述单量子比特的噪声控制操作。量子技术具有彻底改变科学和技术的潜力。例如，可以测量单个核自转的量子设备似乎触手可及。然而，这种令人惊叹的技术的主要障碍是背景噪音。由于缺乏理论工具，噪声在装置设计中被忽略，其后果只能在实际实验中检验。这项提议的主要目的是能够对已经在设计阶段的噪声进行建模，从而能够以数量级来优化性能和稳定性。该项目通过开发抗噪音和噪音辅助控制方法，解决了几个雄心勃勃的短期目标。使用最先进的高性能计算机将能够表征钻石杂质，从而有助于设计更高效的量子测量设备。PI已经与同意分享控制设置和参数细节的领导小组进行了联系。更广泛地说，噪声设备中可达操作的数据库和开源算法的开发将使数值研究适用于其他量子技术的实现，如离子陷阱。控制噪声系统的主要挑战是在存在控制的情况下模型的有效性。这个项目将把受控噪声系统的建模建立在严格的理论基础上。误差范围将使用开放量子系统中成熟的工具来得出。这些界限将被用来推导出一套标准，在这套标准下，控制频率弱耦合极限林布拉迪亚仍然是一个好的模型。然后，我们将知道在实验案例研究中哪个近似是合理的。控制依赖的有趣结果是，在标准过程层析成像中被认为不可观察的镀液的性质将通过控制而变得可见。最后，从理论的角度来看，开发更好的噪声控制分析工具也是很重要的。由于量子操作的复杂数学结构，这一点到目前为止一直难以捉摸。本提议的目的是考虑混合控制的新范例，例如施加从一组脉冲中随机选择的脉冲，从而在可达操作中施加凸起结构。这将大大简化低维系统中的噪声控制。它还为实现所谓的不可分解操作铺平了道路，这些操作以前被认为是受控量子设备无法达到的，最近受到了相当大的关注。

The current project will characterise the performance of controlled quantum devices in the presence of noise through extensive numerical computations and a new paradigm of control. This is important for emergent quantum technology where noise is a major obstacle. The aims of the project are the numerical characterisation of the operations that can be reached in noisy single and two qubit experiments, the development of estimation techniques and better controls for noise, and a simpler analytical toolbox to describe noisy control operations of single qubits.Quantum technology has the potential to revolutionise science and technology. For example quantum devices that can measure individual nuclear spins seem just about within reach. The main obstacle for such amazing technology is however background noise. Because of a lack of theoretical tools, noise is ignored at the device design and its consequences can only be tested in the actual experiment. The main aim of this proposal is to enable the modelling of the noise already at design stage, thereby allowing to optimize performance and stability by orders of magnitude. The project addresses several ambitious short-term goals by developing noise-resistant and noise-aided methods of control. Using state-of-the-art high performance computers will enable the characterisation of diamond impurities and thereby aid the design of more efficient quantum measurement devices. The PI is already in contact with leading groups who have agreed to share details on the control set-up and parameters. More generally a database of reachable operations in noisy devices and the development of an open source algorithm will make the numerical studies applicable to other implementations of quantum technologies, such as ion traps.The main challenge of controlling noisy systems is the validity of the model in the presence of control. This project will put the modelling of controlled noisy systems on a rigorous theoretical footing. Error bounds will be derived using well established tools from open quantum systems. These bounds will be used to derive a set of criteria under which control frequencies the weak coupling limit Lindbladian remains a good model. We will then know which approximation is justified in the experimental case studies. The interesting consequence of the control dependence is that properties of the bath which would be considered unobservable in standard process tomography will become visible through controls. Explicit methods for estimating noise parameters will be discovered this way.Finally from a theoretical perspective it is also important to develop better analytical tools for noisy control. This has been elusive so far because of the complicated mathematical structure of quantum operations. The aim of the present proposal is to consider the new paradigm of mixed controls, e.g. applying pulses chosen randomly from a set of pulses, and thereby imposing a convex structure in the reachable operations. This will substantially simplify noisy control in low-dimensional systems. It also paves the way to implement so-called non-decomposable operations, which were previously considered unreachable for controlled quantum devices, and which received considerable attention recently.