Mobile atom traps based on domain walls in magnetic nanowires

物理学最近最戏剧性的进展之一是通过实验实现了物质的新状态，这是使用激光将原子冷却到绝对零度的百万分之一以内的结果。激光冷却技术的发展是1997年诺贝尔物理学奖的主题，而一种新的物质状态--玻色-爱因斯坦凝聚体的实现，导致了2001年的诺贝尔奖。在这个研究项目中要冷却的原子可以被认为是微小的条形磁铁(它们是顺磁原子)，在非常低的温度下，可以使用相对较小的磁场来捕获它们。另一个完全不同的最近的发展是平面磁性纳米线技术的进步。这些导线的延伸几何形状限制了磁化作用沿导线的长度。当相反的磁化方向在纳米线中相遇时，它们被一个称为“磁区壁”的过渡区隔开。这些域壁可以利用外部施加的磁场通过纳米线电路移动，但它们本身也是磁场的来源。我们最近展示了如何利用纳米线中的域壁的磁场来捕获激光冷却的原子。在这个提议中，我们的目标是通过实验演示和研究利用纳米线中的域壁来捕获原子。捕获在纳米线上方的冷原子将被牢牢地限制，更关键的是，由于可以精确地控制域壁的位置，这些原子可以移动。这是进一步研究控制相邻俘获原子之间相互作用的极好平台。在新兴的量子信息处理(QIP)领域中，两个原子可以通过拉近和分离来实现纠缠。此外，一个基本纳米线电路单元的许多相同副本可以被镶嵌以创建量子计算网络。这一提议还提供了在其他重要研究领域的应用。磁畴壁的纳米级导致被捕获的原子距离衬底不到一微米。改变外加磁场的大小可以控制原子-表面的精确高度，因此可以设想使用磁化-壁原子陷阱来研究原子-表面的相互作用。开发可移动的纳米磁原子陷阱为更复杂的量子物体提供了一种先驱技术，并将其应用于新的科学，如表面的量子碰撞，或新的技术，如量子信息处理。

One of the most dramatic recent advances in physics has been the experimental realization of new states of matter as a consequence of using lasers to cool atoms to within a millionth of a degree of absolute zero. The development of laser-cooling techniques was the subject of the 1997 Nobel Prize in Physics, and the realization of a new state of matter, a Bose-Einstein Condensate, resulted in the 2001 Nobel Prize. The atoms to be cooled in this research project can be though of as tiny bar magnets (they are paramagnetic atoms), and at very low temperatures it is possible to trap them using relatively small magnetic fields.A quite separate recent development has been the advance of planar magnetic nanowire technologies. The extended geometry of these wires constrains magnetisation to lie along the wire length. When opposite magnetisation directions meet in a nanowire, they are separated by a transition region termed a 'domain wall'. These domain walls can be moved through nanowire circuits using externally applied magnetic fields but they are also themselves a source of magnetic field. We have recently shown how the magnetic field from a domain wall in a nanowire can be used to trap laser-cooled atoms.In this proposal, we aim to demonstrate experimentally and investigate atom trapping using domain walls in nanowires. The cold atoms trapped above a nanowire will be robustly confined and, crucially, mobile due to the precision with which the position of domain walls can be controlled. This is an excellent platform for further research in controlling interactions between neighbouring trapped atoms. In the burgeoning field of Quantum Information Processing (QIP) two atoms can be entangled by bringing them close and subsequently separating them. Furthermore, many identical copies of a fundamental nanowire circuit unit can be tessellated to create quantum-computing networks.This proposal also offers applications in other important research areas. The nanometre scale of the magnetic domain wall results in the trapped atoms being closer than a micrometre to the substrate. Varying the magnitude of external magnetic fields allows control of the exact atom-surface height, hence it is envisaged that domain-wall atom traps will be used to study atom-surface interactions. Developing a mobile nanomagnetic atom traps provides a precursor technology to more complicated quantum objects, and their application to new science, such as quantum collisions on surfaces, or new technologies, such as quantum information processing.