Small-Scale Ring Traps for Atom Interferometry and Quantum Fluid Investigations

光学干涉仪作为一种灵敏的测量工具的使用可以追溯到一个多世纪前迈克尔逊和莫利的实验。随着激光(相干光源)的发明，光学干涉术已经发展成为一种普遍存在的技术，用于精确测量位置、加速度和(通过萨尼亚克效应)旋转等量。在这些技术进步的同时，通过量子力学的发展，人们对物质有了更基本的理解。这里的一个关键概念与我们的经典理解不同，那就是物质的波动性质。人们意识到，实际上只有在极低的温度下才能观察到原子波。然而，激光现在已经提供了实现这一点的工具；原子样本距离绝对零度不超过百万分之一度，实际上也是激光本身的原子等价物，原子的相干来源被称为玻色-爱因斯坦凝聚体，BEC。我们现在有了将干涉和冷原子这两个概念结合起来的工具：原子干涉计量学。然而，关键的一点是原子干涉测量的范围更广(对引力场和电磁场的灵敏度)，最重要的是更高的灵敏度。对于Sagnac干涉仪，灵敏度与所涉及的粒子的相对论能量成正比，原子的相对论能量通常比光子的大10个数量级以上。本提议的目的是开发原子等效的Sagnac干涉仪，在重力测量和惯性传感方面具有潜在的应用。实现这一点的平台将是一个完美的圆柱形对称环形陷阱，其中BEC可以分成两部分，这两部分沿相反的方向移动，然后重新组合，通过累积的相位差揭示外部影响的效果。环形陷阱是基于我们从理论上研究过的一个新概念。金属环被放置在一个正弦变化的磁场中。在环中感应电流，从而在环周围产生磁场。这与最初的感应场一起，在环的内侧产生了一个光滑、对称和稳定的磁陷阱，冷原子和BEC可以被捕获在那里。这种几何结构的简单性和健壮性使其成为一种有吸引力的实用测量设备。下一步涉及小型化，这一概念是过去几十年电子和电信等技术进步的根源。微制造技术允许器件制造的大规模并行性，这不仅简化了干涉仪的结构，而且提供了测量冗余和校正系统误差的手段。我们计划微制造电感耦合环形陷阱，并展示它们作为原子干涉仪的用途。

The use of an optical interferometer as a sensitive tool for measurements dates back to the experiments of Michelson and Morley over a century ago. With the subsequent invention of the laser, the coherent source of light, optical interferometry has been developed into a ubiquitous technology for precision measurements of quantities such as position, acceleration and (through the Sagnac effect) rotation. In parallel with these technological advances a more fundamental understanding of matter was gained through the development of quantum mechanics. One of the key concepts here, at odds with our classical understanding, is the wave nature of matter. It was realised that atomic waves in practice would only be observable at extremely low temperatures. However, lasers have now provided the tools for realising just that; samples of atoms a millionth of a degree or less from absolute zero and indeed also the atomic equivalent of the laser itself, the coherent source of atoms known as a Bose-Einstein condensate, BEC. We now have the tools to combine two concepts of interference and cold atoms: atom interferometry. The crucial points, however, are the wider scope of atom interferometry (sensitivity to e.g. gravitational and electro-magnetic fields) and above all the superior sensitivity. For a Sagnac interferometer the sensitivity is proportional to the relativistic energy of the 'particle' involved, which is typically more than 10 orders of magnitude larger for atoms than for photons.The aim of the present proposal is to develop the atomic equivalent of the Sagnac interferometer with potential applications in gravitational measurements and inertial sensing. The platform for this will be a perfectly cylindrically symmetric ring trap where a BEC can be split in two parts, that traverse in opposite directions and then recombine to reveal the effect of external influences through an accumulated phase difference. The ring trap is based on a novel concept we have investigated theoretically. A metal ring is placed in a sinusoidally varying magnetic field. A current is induced in the ring, which produces a magnetic field around the ring. This together with the original inducing field produces a smooth, symmetric and stable magnetic trap on the inside of the ring, where cold atoms and BEC's can be trapped. The simplicity and robustness of this geometry makes it an attractive candidate for a practical measurement device. The next step involves miniaturisation, the concept at the root of the last few decades' advances in technologies such as electronics and telecommunications. Micro-fabrication techniques allow for massive parallelism of device manufacture, which not only simplifies the construction of interferometers, but also provides redundancy of measurement and a means for correction of systematic errors. We plan to micro-fabricate inductively coupled ring traps and demonstrate their usefulness as atom interferometers.