This thesis is concerned with the development of an intermediate magnetic field "clock-qubit" in <sup>43</sup>Ca<sup>+</sup> at 146G and techniques to manipulate this qubit using microwaves and lasers. While <sup>43</sup>Ca<sup>+</sup> has previously been used as a qubit, its relatively complicated level structure - with a nuclear spin of 7/2 and low-lying D-states -- makes cooling it in the intermediate field an intimidating prospect. As a result, previous experiments have used small magnetic fields of a few gauss where coherence times are limited and off-resonant excitation is a significant source of experimental error. We demonstrate a simple scheme that allows <sup>43</sup>Ca<sup>+</sup> to be cooled in the intermediate field without any additional experimental complexity compared with low fields. Using the clock-qubit, we achieve a coherence time of T<sup>*</sup><sub style='position:relative;left:-.5em;'>2</sub> = 50 (10)s - the longest demonstrated in any single qubit. We also demonstrate a combined state preparation and measurement error of 6.8(6)x 10<sup>-4</sup> - the lowest achieved for a hyperfine trapped ion qubit [NVG<sup>+</sup>13] - and single-qubit logic gates with average errors of 1.0(3) x 10<sup>-6</sup> - more than an order of magnitude better than the previous record [BWC<sup>+</sup>11]. These results represent the state-of-the-art in the field of single-qubit control. Moreover, we achieve them all in a single scalable room-temperature ion trap using experimentally robust techniques and without relying on the use of narrow-linewidth lasers, magnetic field screening or dynamical decoupling techniques. We also present work on a recent scheme [OWC<sup>+</sup>11] to drive two-qubit gates using microwaves. We have constructed an ion trap with integrated microwave circuitry to perform these gates. Using this trap, we have driven motional sideband transitions, demonstrating the spin-motion coupling that underlies the two-qubit gate. We present an analysis of likely sources of experimental error during a future two-qubit gate and the design and preliminary characterisation of apparatus to minimise the main error contributions. Using this apparatus, we hope to perform a two-qubit gate in the near future.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:618425 |
| Date | January 2013 |
| Creators | Harty, Thomas P. |
| Contributors | Lucas, David M. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:55264c2d-bb42-4439-bf49-731b9f66de74 |
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