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Title: Quantum chaos in cold atoms and spin waves : the double kicked rotor
Author: Stocklin, M.
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2008
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The Kicked Rotor is a well studied example of a classical Hamiltonian chaotic system, where the momentum of a particle is altered periodically in time through a series of external impulses or kicks, forming a sinusoidal potential. In the chaotic regime this results in a diffusion mechanism, where the average energy of an ensemble of particles grows linearly in time, including certain corrections to the diffusion rate, arising from correlations between kicks at different times. This system has a quantum analogue, the Quantum Kicked Rotor, which exhibits the phenomenon of dynamical localization (DL), a quantum destructive interference effect, where the average energy increase is halted after a given time, and an asymptotic exponential momentum distribution is obtained. Experiments have been performed using ultracold atoms and standing waves of laser light. This thesis investigates the newly discovered Double Kicked Rotor, where pairs of closely spaced kicks are applied to particles. This results in momentum space being divided into a number of cells in which fast energy absorption occurs, whereas at the cell boundaries, termed momentum trapping regions, particles absorb almost no energy. It is shown that the effect is almost entirely independent of the time interval between the kick pairs. It is further shown that the diffusion mechanism is due to a strong momentum dependence of the kick correlations. Novel global long-range correlations in time are found to control the system behaviour significantly - a very unusual situation for a chaotic system. The Quantum Double Kicked Rotor is also investigated, both in the context of laser pulses applied to cold atoms and magnetic fields applied to Heisenberg spin chains. Trapping in momentum and position space occurs respectively, and DL results in an asymptotic imprint of the asymmetries in momentum or spin distributions. The classical diffusion calculations are used to explain the experimental results. Novel scaling properties are also discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available