Phase Locked Atomic Interferometers for Gravity Gradiometry

精确的重力测量可以揭示我们周围隐藏结构的有趣而重要的细节。由于重力不能被屏蔽，一种能够被动地进行这种测量的工具有许多应用，从测量地球的大地水准面到勘测地下人造结构.量子技术的发展使原子能够用作惯性传感器，大大提高了这些测量的准确性和精度。这些装置工作的关键过程是通过下落原子并测量其多普勒频移的变化来检测加速度。重力梯度测量法测量的是两个选定点之间的重力差，而不是单个位置的绝对值。这具有抑制共模噪声的好处，共模噪声是绝对和相对测量中的一个问题，对于实验室以外的应用来说是一个严重的问题。重要的是，这两个位置由刚性基线连接，并由同一光场寻址。目前的原子干涉仪使用一个单一的拉曼光束通过两个原子云，以消除这种共模噪声。这些原子云通常在同一个真空室中。不幸的是，这限制了这种设备的几何形状和便携性，使它们不适合许多实际应用，因为两个原子云必须彼此有视线，超高真空系统体积庞大且耗电。该项目旨在通过将原子云分离到单独的真空室并将其与稳定的光纤干涉仪连接来解决这些问题。主动光纤干涉仪将作为一个锁相机制来保持拉曼光束的相关性，从而保持两个原子云的相关性。因此，在两个原子云之间没有视线的情况下，可以抑制共模噪声。这遵循了原子钟中用于分配光学相位的技术，并证明了这一努力所需的稳定性水平。以这种方式分离原子云使我们具有很大的灵活性和可移植性;使这样的设备适合实际应用。

Accurate measurements of gravity can reveal intriguing and important details of the hidden structure ofour surroundings. Since gravity cannot be shielded a tool which can passively make such measurementshas many applications; from measuring the geoid of the earth to surveying subterranean man-madestructures. Developments in quantum technology have enabled the use of atoms as inertial sensors whichgreatly increases the accuracy and precision of these measurements. The key process of how thesedevices work is by dropping atoms and measuring the change in their Doppler shift to detect acceleration.Gravity gradiometry measures the difference of gravity between two chosen points rather than theabsolute value at a single position. This has the benefit of rejecting common-mode noise, a problemin absolute and relative measurements and a serious issue for applications outside of the laboratory. Itis important that the two locations are connected by a rigid baseline and are addressed by the samelight field. Current atomic interferometers use a single Raman beam passing through both atom cloudsto eliminate this common-mode noise. These clouds are typically in the same vacuum chamber.Unfortunately this limits geometry and portability of such devices, making them unsuitable for manypractical applications, as the two atom clouds must have line of sight to each other and ultra-high vacuumsystems are bulky and power hungry.This project aims to address these problems by separating the atom clouds into separate vacuumchambers and connecting them with a stabilised optical fibre interferometer. The active optical fibreinterferometer will behave as a phase-locking mechanism to maintain the correlation of the Raman beamsand hence the correlation of the two atom clouds. Thus allowing the rejection of common-mode noisewithout line-of-sight between the two atom clouds. This follows a technique used in atomic clocks fordistributing optical phase and demonstrates the required stability levels for this endeavour. Separatingthe atom clouds in this manner enables us a great deal of flexibility and portability; making such a deviceideal for practical applications.