  This dissertation treats the topics of threshold calculation, ancilla
construction, and non-standard error models. Chapter 2 introduces background
material ranging from quantum mechanics to classical coding to thresholds for
quantum computation. In Chapter 3 numerical and analytical means are used to
generate estimates of and bounds on the threshold given an error model
described by a restricted stochastic Pauli channel. Chapter 4 develops a
simple, flexible means of estimating the threshold and applies it to some cases
of interest. Finally, a novel method of ancilla construction is proposed in
Chapter 5, and the difficulties associated with implementing it are discussed.
