This thesis presents an experimental investigation into the properties of highly doped (<i>n<sub>phosphorous </sub></i> ~ 1.4 x 10<sup>19</sup><i>cm<sup>-</sup></i><sup>3</sup>) n-type silicon-germanium double quantum dots. The structures are fabricated with a diameter of between 40nm and 70nm by means of electron beam lithography. Their electronic properties are then measured using a variety of cryogenic techniques, including a dilution refrigerator with a base temperature of 20mK. The main results from this investigation are described below. The ‘Coulomb Oscillations’ form a hexagonal lattice as the electrochemical potentials on the two dots are shifted by means of electrostatic gates. This indicates that the double dot is indeed a double well potential, and shows that the electron number on the dots can be independently altered. The elastrostatic gates are shown to have a wide degree of control over not just the electrochemical potential on the dots, but also the shape of the potential well. In this way, the two wells can be induced to coalesce; one of the wells can be merged into its nearby lead; or the coupling parameters between the dots and dots and leads can be altered. A supplementary piece of work, undertaken in collaboration with Paul Cain, is presented in appendix A. This describes an original scheme for quantum computation in which the ammonia molecule is used as the qubit. It is confined within a fullerene and placed on a crystal surface where gates and global microwave pulses manipulate, and interact it with other such encapsulated ammonia molecules. Finally, measurements is performed with an electrometer which has the ability to distinguish the polarisability of the ammonia molecule’s eigenstates.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598980 |
| Date | January 2003 |
| Creators | Ferguson, A. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0083 seconds