Nuclear Nanomagnets for Quantum Optical Spin Devices

用于量子计算的核纳米磁体当今的信息技术涉及通过一个由细导线和半导体晶体管组成的系统来操纵和传输少量电荷。制造更快、更便宜的计算机意味着使这些元件更小——事实上，它们的尺寸每两年减半一次，很快我们就会达到晶体管与原子本身一样大小的极限！电子可以被认为是粒子或波，而电子波的大小决定了它在如此小的元件中的行为。量子力学，描述如此小的系统的物理学，预言如此小的组件中的电子将具有完全不同的性质，我们将不得不以一种全新的方式设计我们的组件。理解如何处理电子的量子行为为我们提供了制造一种新型计算机的机会。研究人员已经证明，利用电子和光的纯量子性质，量子计算机在理论上是可能的。这些量子计算机仍处于非常早期的阶段，但总有一天它们将执行传统计算机永远无法完成的计算。我计划的研究将涉及研究一种新型的量子计算机架构。在量子计算机中，信息必须以可靠的方式存储和传输。我将展示通过将单个电子放入量子点中来存储信息是可能的。这是一种纳米级半导体，可以存储单个电子，并防止它与其他电子相互作用或碰撞，从而丢失其信息。事实证明，在电子中存储信息的最好方法是将其编码到自旋中。自旋是电子的内在磁体。我们可以改变它的方向从上到下，就像计算机中的比特有0或1的值一样。电子自旋是在量子点中存储信息的一种很好的方式，但事实上我们不能永远存储电子自旋。问题是电子位于由原子核晶格组成的半导体中。这些原子核中的每一个都有自己的自旋，这是电子能感觉到的。每个原子核的磁场都很弱，但最终电子的自旋会因为这些原子核而改变。另一方面，在我的工作中，我将利用原子核。一般来说，核自旋指向各个方向，但也有可能使用电子重新定向所有的原子核，使它们指向同一个方向。我们的量子点里大约有10000个原子核，所以把它们排列起来意味着电子感受到的磁场现在非常大。原子核现在对电子自旋有正的影响。所有的东西都在同一个方向上排列，电子自旋可以储存很长时间。解决如何存储电子自旋的问题是不好的，然而，如果我们不能读出它的状态并传输到另一个电子自旋来执行计算。幸运的是，量子点中的电子能够吸收和发射光，当它们这样做的时候，它们也会把关于它们自旋的信息传递给我们能够探测到的单个光子（一种光粒子）。唯一的问题是等待电子产生光子需要很长时间。为了使电子更快地吸收和发射光子，我们将它们放入控制光子与电子相互作用的光子结构中。在我的工作中，我将设计光子结构和技术，不仅如此有效，我将能够制造一个非常强大的纳米磁铁，而且还非常敏感，我将探测到一个单一的原子核。这项工作不仅将帮助我们理解如何使用半导体制造量子计算机，还将告诉我们很多关于如何在其他系统中使这些基本相互作用发挥作用的信息。

Nuclear Nanomagnets for Quantum ComputingInformation technology today involves manipulating and transporting small collections of charges through a system of small wires and semiconductor transistors. Making faster and cheaper computers means making these components smaller - in fact their size is halving every two years, and soon we will reach the limit where transistors are the same size as the atoms themselves! Electrons can be thought of as being like a particle or like a wave, and it is the size of the electron wave that determines its behaviour in such small components. Quantum mechanics, the physics that describes such small systems, predicts that electrons in such small components will have totally different properties, and we will have to design our components in a completely new way.Understanding how to deal with the quantum behaviour of electrons presents us with the opportunity to make a new type of computer. Researchers have shown that a quantum computer is theoretically possible by making use of the purely quantum nature of electrons and light. These quantum computers are still in their very early stages, but one day they will perform calculations that will never be possible with conventional computers. My intended research will involve investigating a new type of architecture for a quantum computer. In a quantum computer, information must be stored and transmitted in a reliable way. I will show that it is possible to store information by putting a single electron into a quantum dot . This is a type of nanoscale semiconductor that can store a single electron, and prevent it from interacting or colliding with other electrons and losing its information. It turns out that the best way to store information in the electron is to encode it into its spin . Spin is the intrinsic magnet of an electron. We can change its direction from up to down , in the same way that bits in a computer have the value 0 or 1 .Electron spin is a very good way to store information in quantum dots, but in fact we cannot store the electron spin forever. The problem is that the electron sits inside a semiconductor, which consists of a lattice of atomic nuclei. Each of these nuclei also has its own intrinsic spin, which the electron feels. The magnetic field from each nucleus is very weak, but eventually the electron spin will change due to these nuclei. In my work, on the other hand, I am going to make use of the nuclei. Generally, the nuclear spins point in all directions, but it is also possible to use the electron to redirect all the nuclei to point in the same direction. There are about 10000 nuclei inside our quantum dot, so aligning them all means that the magnetic field felt by the electron is now very large. The nuclei now have a positive effect on the electron spin. Everything is aligned in the same direction and the electron spin may be stored for extremely long times.Solving the problem of how to store electron spins is no good, however, if we are not able to read out and transport its state to another electron spin to perform a calculation. Fortunately, electrons in quantum dots are able to absorb and emit light, and when they do this they also give the information about their spin to a single photon (a particle of light) which we are able to detect. The only problem is that waiting for the electron to produce a photon takes a long time. To make electrons absorb and emit photons faster, we put them into photonic structures that control how the photons interact with the electrons. In my work I will design photonic structures and techniques that are not only so effective that I will be able to either make a very strong nanomagnet, but also so sensitive that I will detect just a single nucleus. This work will help us to understand not only how to make quantum computers using semiconductors, but will tell us a great deal about how to make these basic interactions work in other systems as well.