Matterwave interferometry for inertial sensing

导航是一个难题，特别是在进入天空受到限制的情况下。目前，大多数国际旅行的飞机和船舶依赖于通过GPS（全球定位信号）信号，这是由24颗卫星在地球轨道上提供的位置。如果这个信号丢失了，就像古代的水手看不到星星一样，那么旅行者很快就会失去他们的位置。鉴于GPS由一个国家拥有和运营，美国可以随时关闭它，而且它对黑客开放，很明显需要一种完全独立的位置知识的方法。该项目的目的是通过使用原子物理学新开发的工具，利用最先进的精密测量技术，生成具有比最先进灵敏度更好的纯被动位置跟踪方法。原子受到惯性力的强烈影响，即突然加速时的“推动”效应。这种效应已经被用来测量重力，测量物体下落一定距离所需的时间可以让我们检测到地球质量所施加的力。在过去的几十年里，激光物理学已经取得了巨大的进步，允许通过光学干涉测量法以亚原子分辨率测量位置，这使得对力的测量灵敏度也有了类似的提高。然后，解决方案是使用众所周知的牛顿定律对瞬时速度和位置进行积分。然而，所需的灵敏度是极其严格的-10-5 m/s2的误差（重力加速度的百万分之一）导致在短短一小时内100 m的位置漂移，在一天内约50 km。解决方案是使用量子技术;物质波干涉仪。近年来，利用激光将原子冷却到只有几微米K的能力使原子物理学取得了一些最引人注目的发展。其中最深刻的是对原子的布罗意波性质的直接观察和随后的玻色-爱因斯坦凝聚（BEC）的实现，BEC是一种物质状态，其中原子云合并成单个量子态[1]。使用这些相干物质波的干涉的可能性为测量设备提供了新的潜在精度水平。感兴趣的一个特定应用是惯性感测与基于量子的自主导航设备中的应用。斯特拉斯克莱德大学物理系的实验量子光学和光子学小组一直在该领域的研究中处于领先地位，并展示了原子干涉测量的新的不同方法。事实上，这个小组的成员在英国也是苏格兰的第一个BEC。该项目将建立在斯特拉斯克莱德大学现有的研究基础上，利用相干物质波进行原子干涉测量，并致力于环形导向陷阱，以探索开发旋转传感技术的可能性。该项目的核心将是与斯特拉斯克莱德的微加工技术的集成[2]，该技术是最近开发的，用于激光冷却装置的光学装置的集成。该项目的目标将是演示环形阱几何结构中的物质波Sagnac干涉仪。限制在环形阱中的相干物质波系统在形式上等价于从环形激光陀螺已知的环形腔中的相干光场（激光）[3]。然而，有趣的区别在于，对相位旋转的敏感性与所涉及的粒子/波的相对论能量成比例。对于原子来说，它比光大11个数量级。该项目将建立在斯特拉斯克莱德的独特经验，在产生一个环形，顺利捕获潜力，原子波可以在相反的方向传播（4，5）。

Navigation is a difficult problem, especially when access to the skies is restricted. Currently, most international travel by plane and ship relies on location through the GPS (Global Positioning Signal) signal, which is provided by a fleet of 24 satellites in orbit around Earth. If this signal is lost then, much like ancient sailors without sight of the stars, then the traveller very quickly loses track of their position. Given that GPS is owned and operated by one country, the USA, who can switch it off at any time and, furthermore, that it is open to hacking, it is clear that a means to have completely independent knowledge of location is required. The aim of this project is generate purely passive methods of tracking position with better than state-of-the-art sensitivity by the using of newly developed tools from atomic physics that harness the state-of-the-art in precision measurement. Atoms are strongly affected by inertial forces, the "pushing" effect that is felt when suddenly accelerating. This effect is already used to measure gravity, where measuring the time it takes for an object to fall a certain distance allows us to detect the force exerted by the mass of the Earth. Huge advances have been made in laser physics the last decades that allow measurement of positions with sub-atomic resolution through optical interferometry, which allows for similar increases in sensitivity to measurement of forces. The solution then is to use the well-known laws of Newton to integrate back the instantaneous velocity and position. However, the sensitivity required is extremely strict - an error of 10-5 m/s2 (one millionth of the acceleration due to gravity) results in a drift in position of 100 m in just one hour, and of approximately 50 km in one day. The solution is to use a quantum technology; the matter-wave interferometer. The ability to cool atoms down to only a few micronK using laser light has enabled some of the most spectacular developments in atomic physics in recent years. One of the most profound is the direct observation of the de Broglie wave nature of atoms and the subsequent achievement of a Bose-Einstein condensate (BEC), a state of matter where a cloud of atoms coalesce into a single quantum state [1]. The possibility of using interference of these coherent matter waves offers new levels of potential accuracy for measurement devices. A particular application of interest is that of inertial sensing with applications in quantum-based autonomous navigation devices. The Experimental Quantum Optics and Photonics group within the Physics Department at the University of Strathclyde have been leading in research in this area and have demonstrated new different methods for atom interferometry. In fact, members of this group produced the first BEC in the UK also the first in Scotland. This project will build on existing research at Strathclyde University in atom interferometry with coherent matter waves and work on ring-shaped guided traps to explore the possibilities for developing miniaturised technology for rotation sensing. Central for this will be integration with Strathclyde's microfabrication technology [2], which was recently developed for miniaturisation of the optical set-up for laser cooling setup.The goal of the project will be the demonstration of a matter-wave Sagnac interferometer in a ring-trap geometry. The system of a coherent matter wave confined in a ring trap is formally equivalent to the coherent optical field (laser) in a ring cavity known from the ring laser gyro [3]. The interesting difference, though, is that the sensitivity to phase rotation scales with the relativistic energy of the particle/wave involved. For atoms that is about eleven orders of magnitude larger than light. The project will build upon Strathclyde's unique experience in generating a toroidal, smooth trapping potential, where atomic waves can propagate in opposite directions (4,5).