Understanding and engineering dissipation in nanoscale quantum devices

技术进步的进步为我们提供了更小、更复杂的设备：例如，与25年前的型号相比，今天的智能手机在尺寸和功能范围上几乎认不出来了。这一进展已经把我们带到了这样一个地步：现在必须根据设备组成粒子的量子行为来理解设备，这是技术的一个新前沿，进一步将导致全新的应用。然而，建立设备的完全量子力学模型是出了名的困难：描述量子系统所需的信息量与其大小呈指数级增长。当人们必须考虑环境如何与设备交互时，情况就更糟了，但这对真实设备来说是一个关键的考虑因素。然而，我们最近开发了一种新的量子模拟技术，效率非常高：通过只保留最重要的信息，我们能够跟踪单个粒子的行为，即使它与环境中的所有其他粒子相互作用非常强烈。在这个项目中，我们将利用这一新技术来设计、模拟和优化具有不同技术应用的四种类型的纳米设备。所有这些设备的功能都依赖于类似的物理学，即设备如何与环境相互作用。因此，我们的新方法非常适用于所有这些领域。首先，我们将对固态单光子源进行建模。它们产生的光-光子-一次一个，并为未来的安全通信和量子计算的想法奠定了基础。我们将发现光子和固体振动之间的耦合是如何决定它们的性能的。理解这一点将使我们能够确定设备，无论是加工成细线或薄膜，还是绘制成固体基质中的纳米图案，如何才能创造出更有效的光子源。其次，太阳能电池板需要首先从太阳吸收光能，然后将其传输到电极。我们将研究这个能量传输问题的量子力学，特别是有机材料制成的太阳能电池。在这里，振动与传输能量的激发电子之间的耦合非常强烈，我们的新技术非常适合研究这一过程是如何工作的，以及如何通过知情选择组成有机分子来改善这一过程。第三，如果我们能够使用分子建立电路，电子学的一个新前沿将成为可能。因此，电流是电子如何以量子力学方式从一个分子隧道到另一个分子的结果；这既取决于分子之间的电子耦合，也取决于分子的振动方式。我们将使用我们的技术来建立分子结的模型，并探索强电子和振动耦合如何改变这些材料的量子传输特性。第四，钻石最近处于一种全新成像技术的前沿。特别是，钻石中的单电子有一个微小的磁矩--自旋，它的运动取决于电子所在位置的磁场有多强。值得注意的是，单电子的自旋可以在钻石中测量，因此纳米级精度的磁成像是可能的。这些“纳米磁力计”工作的极限取决于它们与周围环境隔离的程度。在这个项目中，我们将首先使用我们的新方法来了解自旋与其环境耦合的动力学，然后展示如何更有效地分离自旋。该项目将推进几种不同的纳米技术，同时我们将开发一种独特的、免费可用的工具，在未来可以应用于大量的新系统。

The march of technological progress has given us devices that are ever smaller and more complex: today's smart phones for example are almost unrecognizable in their size and their range of functions from the models of 25 years ago. This progress has taken us to the point where devices must now be understood in terms of the quantum behaviour of their constituent particles, a new frontier in technology that furthermore will lead to completely new applications.However, building fully quantum mechanical models of devices is notoriously difficult: the amount of information needed to describe a quantum system scales exponentially with its size. The situation is even worse when one must consider how the environment interacts with the device, and yet this is a crucial consideration for real devices. However, we have recently developed a new quantum simulation technique with remarkable efficiency: by keeping just the most important information we are able to track the behaviour of a single particle even when it is interacting very strongly with all of the other particles in its environment. In this project, we will exploit this new technique to design, simulate, and optimize four types of nanoscale devices with various technological applications. The functioning of all these devices relies on similar physics, namely how the device interacts with the environment. As such, our new method is ideally suited to all these areas.First, we will model solid state single photon sources. These produce quanta of light - photons - one at a time, and underpin future ideas for secure communication and quantum computing. We will find how the coupling between the photons and the vibrations of the solid determines affects their performance. Understanding this will allow us to determine how devices, either machined as thin wires or membranes or drawn as nanometre patterns in a solid matrix, could create more effective photon sources.Second, solar panels need to first absorb light energy from the sun, and then to transport it to electrodes. We will investigate the quantum mechanics of this energy transport problem, in particular for solar cells made of organic materials. Here, vibrations are very strongly coupled to the excited electrons that transport the energy, and our new technique is ideal for studying how this process works and how it might be improved by informed selection of component organic molecules.Third, a new frontier in electronics will be enabled if we can build circuits using molecules. Electric current is then a consequence of how electrons can tunnel quantum mechanically from one molecule to the next; this depends both on electronic coupling between molecules and how the molecules vibrate. We will use our technique to build models of molecular junctions, and explore how strong electronic and vibrational coupling changes the quantum transport properties of these materials.Fourth, diamonds have recently been at the forefront of a whole new kind of imaging technology. In particular, single electrons in diamond have a tiny magnetic moment, a 'spin', whose motion depends on how strong the magnetic field is at the position of the electron. Remarkably, the spin of a single electron can be measured in diamond, and so magnetic imaging with nanometre accuracy is a possibility. The limit of how well these 'nano-magnetometers' can work is set by how well they can be isolated from their environment. In this project, we will first use our novel approach to understand the dynamics of a spin coupled to its environment, and then show how to isolate spins more effectively.The project will advance several different nanotechnologies, and at the same time we will develop a unique and freely available tool that can be applied to a huge variety of new systems in future.