Nuclear Nanomagnets for Quantum Optical Spin Devices

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.