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雷的实验。随着激光的发明，相干光源，光学干涉测量已经发展成为一种无处不在的技术，用于精确测量数量，如位置，加速度和（通过Sagnac效应）旋转。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了解。这里的一个关键概念，与我们的经典理解不一致，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；原子的样本距离绝对零度百万分之一度或更少，实际上也相当于激光本身的原子，被称为玻色-爱因斯坦凝聚物（BEC）的原子相干源。我们现在有了结合干涉和冷原子两个概念的工具：原子干涉测量。然而，关键的一点是更广泛的原子干涉测量范围（例如对引力场和电磁场的灵敏度）以及最重要的是优越的灵敏度。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相对论能量大10个数量级以上。本提案的目的是开发具有潜在应用于重力测量和惯性传感的Sagnac干涉仪的原子等效。这个平台将是一个完美的圆柱对称环形陷阱，其中BEC可以分成两部分，在相反的方向上穿越，然后重新组合，通过累积的相位差来揭示外部影响的影响。环形陷阱是基于我们在理论上研究过的一个新概念。将一个金属环置于正弦变化的磁场中。在环中产生电流，在环周围产生磁场。这与原始的感应场一起在环的内部产生了一个光滑、对称和稳定的磁阱，在那里冷原子和BEC可以被捕获。这种几何结构的简单性和鲁棒性使其成为实用测量装置的一个有吸引力的候选者。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。微加工技术允许大量平行器件制造，这不仅简化了干涉仪的构造，而且提供了测量冗余和系统误差校正的手段。我们计划微型制造电感耦合环形陷阱，并证明它们在原子干涉仪中的用途。

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.