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The axioms of quantum physics imply that in general it makes no sense to speak of the long-term behaviour of a quantum walk. In this chapter we introduce a process that allows us to develop a meaningful substitute for a simple average.
To specify a discrete quantum walk on a graph, we need more than just the graph. In general we need some kind of ordering on the edges on each vertex, and this extra structure is closely related to machinery used to describe embeddings of graph in surfaces. in this chapter we explain this connection.
We present applications of the machinery developed in the previous chapter. The applications include examples of perfect state transfer, and a second treatment of Grover’s algorithm.
Aharonov et al. introduced class of quantum walks where the transition matrix is not (in general) a product of two reflections. (We call these shunt-decomposition walks.) In consequence, analysis of these walks is more difficult than the walks met with in earlier chapters. However the state space of walks is still the space of complex functions on the arcs of a graph. We give a description of these walks in graph theoretic terms, and study their behaviour.
1. Grover Search: We introduce the basics of discrete quantum walks, describing some of the underlying physics. One of the most important algorithms in quantum computing is Grover’s search algorithm, we show how one can implement this algorithm using a discrete walk on the arcs of a graph.
To analyse a discrete walk we need to compute the eigenvalues and eigenvectors of unitary matrix. The matrices that arise in practice are products of two reflections. We develop machinery that takes advantage of this structure to complete the specrtal information we need.
Discrete quantum walks are quantum analogues of classical random walks. They are an important tool in quantum computing and a number of algorithms can be viewed as discrete quantum walks, in particular Grover's search algorithm. These walks are constructed on an underlying graph, and so there is a relation between properties of walks and properties of the graph. This book studies the mathematical problems that arise from this connection, and the different classes of walks that arise. Written at a level suitable for graduate students in mathematics, the only prerequisites are linear algebra and basic graph theory; no prior knowledge of physics is required. The text serves as an introduction to this important and rapidly developing area for mathematicians and as a detailed reference for computer scientists and physicists working on quantum information theory.
We present several formulations of the large deviation principle for empirical measures in the V topology, depending on the initial distribution. The case V = B(S) is further studied.