Use this URL to cite or link to this record in EThOS:
Title: Construction of a rubidium fountain atomic interferometer for gravity gradiometry
Author: Tinsley, J. N.
ISNI:       0000 0004 7964 2515
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
Availability of Full Text:
Access from EThOS:
Access from Institution:
Atomic interferometry is a highly precise metrological technique of interest to both fundamental and applied physics. One field in which atomic interferometry is of particular interest is gravimetry, where instruments based upon the controlled manipulation of atomic states have superseded the performance of classical devices. In such devices, a standing wave derived from laser beams with well-defined phase difference are used to impart momentum to atoms undergoing free fall, generating spatial superpositions along the axis of gravity, before returning the atoms to an overlapped final state for recombination. This thesis presents the design and experimental progress towards a gravity gradiometer based upon the interference of rubidium-87 atoms, cooled and launched in a fountain configuration. The fountain is leveraged from a decommissioned frequency standard, which has been re-purposed and redesigned for use as a combined absolute gravimeter and gravity gradiometer package. It is capable of loading 100 billion atoms in 100 ms and then cooling and launching these atoms in a moving molasses configuration, with a final temperature of 5 μK. Furthermore, the process can be quickly repeated, with a second cloud subsequently launched, reaching its apogee at the same time as the first cloud, allowing for the possibility of simultaneous measurement at different heights and, in the future, the inference of the gravity gradient. Control of the fountain is provided by a stable and miniaturised optical setup, allowing for use with a future transportable or field-based device. A Raman beam system to perform the interferometry sequence has been constructed and characterised, likewise designed in a minaturised and stable manner. The Raman beams simultaneously generated Ramsey interference fringes on two independent clouds of atoms -- one launched to a height of 0.7 m and the other to 1 m. Such fringes were clearly observable after 200 ms of evolution time. Mach-Zehnder interference fringes were also demonstrated for dropped and launched atoms, providing the capability for gravimetric measurements to be made once the system has been fully characterised. The principle causes of noise in the Mach-Zehnder cases were identified as arriving from a lack of atoms and the phase noise of the Raman beams. To overcome these challenges, a new Raman beam system has been preliminary designed and tested and a new iteration of the fountain, moving towards quantum degeneracy, has been planned.
Supervisor: Coleman, Jonathon ; Ovchinnikov, Yuri B. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral