Development of a transportable cold atom gradiometer

This work describes the technology developed for the transportable gravity gradiometer, ''GGtop", constructed at the University of Birmingham. The device aims to simultaneously interrogate two physically separated, free-falling cold atom clouds using the technique of Raman interferometry to perform differential gravity measurements. Such a technique will suppress common-mode noise sources, such as vibrations, that otherwise limit classical gravimeters and cold atom interferometers based on single-cloud measurements. The technique is expected to improve speed and sensitivity for field measurements greatly. Using a combination of commercially available components and novel designs, intended to enhance portability and robustness, allowed for demonstration of atomic interference with the apparatus via Ramsey's method of separated oscillatory fields. The achieved fringe contrast of ~2%, defined as the difference in the number of atoms detected in IF = 2>, was limited by drifts stemming from some of the novel designs which prompted continued optimisation of the underpinning subsystems. To address performance issues parts of the experiment were redesigned with the goal of improving reliability at the expense of some portability. Using the retrofitted experiment, interference was once again achieved with fitted fringe spacing of 134.7±2.0 uS in good agreement with the 133.9 uS defined by the experimental control. A factor of 10 improvement in contrast was found with the central fringe demonstrating 18% of the atoms detected in the IF = 2> state when normalised to the total 3D MOT number. The 3.71 ± 0.01 kHz fitted linewidth of the central fringe gives a frequency uncertainty of 5.43 ± 0.01 x 10 - 7. This result leaves the experiment in a good position to begin making measurements of gravity