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Title: A new apparatus for experiments with caesium Bose-Einstein Condensates
Author: Colquhoun, Craig David
ISNI:       0000 0004 8509 9221
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2019
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This thesis reports on the design and construction of an experimental apparatus capable of generating Bose-Einstein condensates (BECs) of spin-polarised caesium-133 atoms. Caesium condensates offer excellent control over interatomic interactions due to the rich landscape of low-field magnetic Feshbach resonances, which enables the study of quantum gases in attractive and repulsive interaction regimes. An ultra-high vacuum system, laser systems and magnetic field coils were assembled to trap and cool the atoms from room temperature to temperatures on the order of 1 nK. Absorption imaging was implemented as a means to detect the number and density distribution of the atoms. Laser cooling and trapping methods are introduced, and the effects of each cooling stage on the gas are demonstrated. The final cooling stage, evaporative cooling, is presented by way of examining the gas after it has undergone each evaporation phase so we observe the onset of Bose-Einstein condensation. Evaporative cooling produces BECs containing on the order of 2×105 atoms, with a condensate fraction of 0.48. We demonstrate that the atom number can be fine-tuned by removal of the most thermal atoms in the trap. We also exhibit our ability to observe expanding condensates in a guiding beam for durations of up to 1 s, and our ability to cause the condensate to implode, by tuning interactions. Measuring the temperature of the gas in sub-nK regimes is currently a challenge when using traditional time-of-flight thermometry. Some modifications to the apparatus have been described, that would permit thermometry using dilute caesium atoms in a different spin state to probe the main gas.
Supervisor: Kuhr, Stefan ; Haller, Elmar Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral