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Title: A Quantum Memory Qubit in Calcium-43
Author: Keitch, Benjamin
ISNI:       0000 0001 3596 4289
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2007
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The hyperfine ground states of a 43Ca+ trapped ion are proposed as a memory qubit. The experimental details to implement such a qubit are presented. These include the design and implementation of a pulse-sequencer to produce pulse sequences for single qubit rotations and other timed experimental sequences. A Raman laser system running at 396nm with a frequency offset of 3.2GHz, based on optically injected violet diode lasers, is presented along with an analysis of its performance. A laser-locking scheme based on the Pound-Drever-Hall method has been built and the design and results are presented here. The dominant limitation on the coherence of the memory qubit, namely fluctuations in the ambient magnetic field, is studied and quantified. The coherence of a superposition of the ground hyperfine clock states of 43Ca+, 11) == SI/2(F =4, MF =0) and IT) == SI/2 (F = 3, MF = 0) is measured using the Ramsey technique. The coherence of the same state after implementing a spin-echo pulse sequence is also measured. The coherence time (T2) for the memory qubit, using the Ramsey technique is found to be 1.2(2)s. With the implementation of a spin-echo sequence, bounds are put on the spin-echo coherence-time as : 2 min ;S T.fE ;S 10 min. The difference in these two results leads to the conclusion that the main source of decoherence is due to magnetic field drift. The 43Ca+ memory qubit has a coherence time that is 104 times greater than current gate times, which is sufficient to reach a regime where fault-tolerant quantum information processing should be possible.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available