paper

Recurrence properties of unbiased coined quantum walks on infinite -dimensional lattices

arXiv:0805.1322 · doi:10.1103/PhysRevA.78.032306

Abstract

The Pólya number characterizes the recurrence of a random walk. We apply the generalization of this concept to quantum walks [M. Štefaňák, I. Jex and T. Kiss, Phys. Rev. Lett. \textbf{100}, 020501 (2008)] which is based on a specific measurement scheme. The Pólya number of a quantum walk depends in general on the choice of the coin and the initial coin state, in contrast to classical random walks where the lattice dimension uniquely determines it. We analyze several examples to depict the variety of possible recurrence properties. First, we show that for the class of quantum walks driven by independent coins for all spatial dimensions, the Pólya number is independent of the initial conditions and the actual coin operators, thus resembling the property of the classical walks. We provide an analytical estimation of the Pólya number for this class of quantum walks. Second, we examine the 2-D Grover walk, which exhibits localisation and thus is recurrent, except for a particular initial state for which the walk is transient. We generalize the Grover walk to show that one can construct in arbitrary dimensions a quantum walk which is recurrent. This is in great contrast with the classical walks which are recurrent only for the dimensions . Finally, we analyze the recurrence of the 2-D Fourier walk. This quantum walk is recurrent except for a two-dimensional subspace of the initial states. We provide an analytical formula of the Pólya number in its dependence on the initial state.

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