Mobile atom traps based on domain walls in magnetic nanowires

物理学最近最引人注目的进步之一，是利用激光将原子冷却到绝对零度的百万分之一以内，从而在实验上实现了物质的新状态。激光冷却技术的发展是1997年诺贝尔物理学奖的主题，而实现一种新的物质状态，玻色-爱因斯坦凝聚，导致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。一个相当独立的近期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沿导线长度的分布。当相反的磁化方向在纳米线中相遇时，它们被一个称为“畴壁”的过渡区域隔开。这些畴壁可以通过外部施加的磁场在纳米线电路中移动，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畴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证明和研究纳米线中使用畴壁的原子捕获。被困在纳米线上方的冷原子将受到严格的限制，而且至关重要的是，由于可以精确控制畴壁的位置，冷原子可以移动。这是一个很好的平台，可以进一步研究如何控制邻近被困原子之间的相互作用。在新兴的量子信息处理（QIP）领域，两个原子可以通过使它们靠近并随后分离而纠缠在一起。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。该方案也可应用于其他重要的研究领域。磁畴壁的纳米尺度导致被困原子离衬底的距离小于1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。开发一种可移动的纳米磁性原子陷阱为更复杂的量子物体提供了一种先导技术，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.