In the study of quantum computation, data is represented in terms of linear
operators which form a generalized model of probability, and computations are
most commonly described as products of unitary transformations, which are the
transformations which preserve the quality of the data in a precise sense. This
naturally leads to "unitary circuit models", which are models of computation in
which unitary operators are expressed as a product of "elementary" unitary
transformations. However, unitary transformations can also be effected as a
composition of operations which are not all unitary themselves: the "one-way
measurement model" is one such model of quantum computation.
In this thesis, we examine the relationship between representations of
unitary operators and decompositions of those operators in the one-way
measurement model. In particular, we consider different circumstances under
which a procedure in the one-way measurement model can be described as
simulating a unitary circuit, by considering the combinatorial structures which
are common to unitary circuits and two simple constructions of one-way based
procedures. These structures lead to a characterization of the one-way
measurement patterns which arise from these constructions, which can then be
related to efficiently testable properties of graphs. We also consider how
these characterizations provide automatic techniques for obtaining complete
measurement-based decompositions, from unitary transformations which are
specified by operator expressions bearing a formal resemblance to path
integrals. These techniques are presented as a possible means to devise new
algorithms in the one-way measurement model, independently of algorithms in the
unitary circuit model.Comment: Ph.D. thesis in Combinatorics and Optimization. 199 pages main text,
26 PDF figures. Official electronic version available at
http://hdl.handle.net/10012/413
