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Title: Quantum optics with a single trapped ion

Abstract: 

This thesis describes experiments carried out on small clouds and single ions of Magnesium confined in a Penning trap. The ions are laser cooled and observed by collection of resonance fluorescence from the cooling transition near 280 nm. 

Initial work concentrated on the Quantum Zeno effect: the inhibition of the decay of an unstable system by frequent measurements. The experiment which was to have been completed involved a single ²⁵Mg⁺ ion. A theoretical overview of the phenomenon is given. The design and analysis of the trap intended for use in this investigation is presented. 

The quantum jump statistics for the three stable isotopes of Mg⁺ have been studied experimentally. The average time which the ion spends fluorescing, 'on' time, was compared to the average time it spends in the dark state, 'off' time to find the On to Off ratio. For both ²⁴Mg⁺ and ²⁶Mg⁺ this value was found to be 16.0 ± 0.7, in agreement with a theoretical value of 16.0.

The presence of hyperfine structure in ²⁵Mg⁺ has two consequences. Firstly, while the jump rate for ²⁴Mg⁺ and 26Mg⁺ remains unaltered for both available cooling transitions, for 25Mg+ the on to off ratio is predicted as 11.8 and 22.8 for the lower and upper transitions respectively. The experimentally measured ratios were: 10.2 ± 1.5 and 22.0 ± 3. Secondly, is the appearance of nuclear quantum jumps. These jumps occur rarely, thus although the data indicate some evidence for nuclear jumps, no firm conclusions can be drawn due to the small number of events observed. 

The first demonstration of the axialization of laser cooled ions in a Penning trap is reported. Axialization allows the coupling of the two radial modes present in the Penning trap, the cyclotron and magnetron motions. Laser cooling is enhanced, causing a substantial redutcion in the radius of the magnetron motion. An ICCD camera was used to image the axialization process for the first time. For a single ion the decrease of the magnetron amplitude corresponds to a reduction in ion temperature to an upper limit of order 10 mK. 

The laser cooled, axialized system exhibits some interesting dynamics which depend critically on the axial drive frequency and amplitude. These were studied using a photon-photon correlation technique. 

 

Issue Date: September 2002

Supervisor: Thompson, Richard

                    Segal, Danny

Item Type:  Physics PhD Thesis