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Permanent link (DOI): https://doi.org/10.7939/R3K931F51

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Characterizing Quantum-Dot Cellular Automata Open Access

Descriptions

Other title
Subject/Keyword
exact diagonalization
extended Hubbard model
molecular scale electronics
quantum-dot cellular automata
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Ritter, Burkhard
Supervisor and department
Beach, Kevin (Physics)
Examining committee member and department
Kennett, Malcolm (Physics, Simon Fraser University)
Marsiglio, Frank (Physics)
Freeman, Mark (Physics)
LeBlanc, Lindsay (Physics)
Department
Department of Physics
Specialization

Date accepted
2014-07-04T13:57:32Z
Graduation date
2014-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
We undertake an in-depth numerical study of quantum-dot cellular automata (QCA), a beyond-CMOS computing paradigm which represents bits as bistable charge distributions in cells consisting of quantum dots. Using semi-realistic but material-independent mod- elling, we characterize the building blocks of QCA circuits in as detailed and unbiased a manner as possible. Starting from an extended Hubbard model, and introducing two controlled Hilbert space truncations whose limits we study and understand, we use exact diagonalization to calculate time-independent properties of small systems. We derive a transverse-field Ising model as an effective description for QCA devices, but find that it is only valid in a restrictive parameter range. We demonstrate that the commonly used intercellular Hartree approximation is inadequate and gives results that are qualitatively incorrect. In contrast to previous work, we show that the response between pairs of ad- jacent cells is linear and does not exhibit gain. Non-linearity and gain only emerge in response to static-charge input cells that have no quantum dynamics of their own. As a consequence, QCA circuits cannot retain a logic state in the thermodynamic limit, and there is a maximum circuit size set by the system’s parameters. Overall, QCA as a com- puting architecture is seen to be more fragile than previously thought. We establish charge neutral cells as a strict requirement for QCA operation. We identify parameter bounds for functional devices: small cell-cell distances, moderate temperatures, and large Coulomb energy scales are necessary.
Language
English
DOI
doi:10.7939/R3K931F51
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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