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Title: The ratchet effect with cold atoms
Author: Edris, Soliman
ISNI:       0000 0004 7965 0793
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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This thesis describes the development and presents the results of a series of experiments on the ratchet effect with laser-cooled caesium atoms in a twodimensional dissipative optical lattice. The ratchet effect describes the directed motion of atoms that are undergoing an unbiased (time-average equal to zero) driving force, which can be realised experimentally using cold atoms in a driven optical lattice. The thesis describes the experimental set-up and methods used to cool and trap atoms in a two-dimensional optical lattice using well-known laser-cooling techniques, as well as the computer software used to control the experiment. It then goes on to present the results of ratchet experiments with cold atoms in the two-dimensional driven optical lattice. Using specific forms of the driving force - namely the biharmonic and splitbiharmonic driving - the atoms undergo directed transport even though the driving forces time-average to zero, corresponding to a manifestation of the ratchet effect. The ratchet transport of the atoms is characterised for various parameters of the driving force. The transport for quasiperiodic driving forces is considered by examining the velocity resonance as a function of relative frequency, and it is shown that the finite duration of the driving becomes a relevant parameter for determining the transport behaviour. An analysis of the structure of the velocity resonance is provided. The results of this work establish that quasiperiodic behaviour can only be guaranteed for long driving times and for those irrational numbers that have poor rational approximations. The final chapter presents the work performed at the National Physical Laboratory on the rubidium atomic fountain in order to measure the rubidium-87 ground-state hyperfine splitting frequency. This work led to a publication [57] and subsequent redefinition [7] of the official value based on those measurements.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available