Mobile atom traps based on domain walls in magnetic nanowires

物理学最近最引人注目的进展之一是实验实现了新的物质状态，这是使用激光将原子冷却到绝对零度的百万分之一度以内的结果。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-爱因斯坦凝聚态的实现则获得了2001年诺贝尔奖。在这个研究项目中被冷却的原子可以被认为是微小的条形磁铁（它们是顺磁性原子），在非常低的温度下，可以使用相对较小的磁场来捕获它们。最近一个相当独立的发展是平面磁性纳米线技术的进步。这些线的延伸几何形状将磁化约束为沿着线长度。当相反的磁化方向在纳米线中相遇时，它们被称为“畴壁”的过渡区域分开。这些畴壁可以通过使用外部施加的磁场的纳米线电路移动，但它们本身也是磁场的来源。最近，我们展示了如何从纳米线畴壁的磁场可以用来捕获激光冷却的原子。在这个建议中，我们的目标是实验证明和研究原子捕获使用纳米线畴壁。纳米线上方的冷原子将被严格限制，并且由于可以精确控制畴壁的位置，因此关键的是，冷原子是移动的。这是进一步研究控制相邻被困原子之间相互作用的绝佳平台。在新兴的量子信息处理（QIP）领域，两个原子可以通过将它们靠近并随后将它们分开来纠缠。此外，一个基本的奈米线电路单元的许多相同的复制品可以镶嵌在一起，以建立量子计算网络。这项建议也提供了其他重要研究领域的应用。纳米尺度的磁畴壁导致被捕获的原子距离衬底不到一微米。改变外部磁场的大小可以控制精确的原子表面高度，因此可以设想畴壁原子陷阱将用于研究原子表面相互作用。开发移动的纳米磁性原子阱为更复杂的量子物体提供了先驱技术，并将其应用于新科学，如表面上的量子碰撞，或新技术，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.