Limit density of 2D quantum walk: zeroes of the weight function

TL;DR

This paper investigates how the probability distribution of a 2D quantum walk can be manipulated by initial conditions and basis choice, enabling suppression of certain peaks and boundary effects in the limit density.

Contribution

It demonstrates how to alter the limit density of a 2D quantum walk to vanish on boundaries or lines, using a basis of eigenvectors of the coin operator.

Findings

Limit density can be made to vanish on boundaries or lines.

Choice of basis simplifies analysis of quantum walk properties.

Suppression of specific peaks in the probability distribution.

Abstract

Properties of the probability distribution generated by a discrete-time quantum walk, such as the number of peaks it contains, depend strongly on the choice of the initial condition. In the present paper we discuss from this point of view the model of the two-dimensional quantum walk analyzed in K. Watabe et al., Phys. Rev. A 77, 062331, (2008). We show that the limit density can be altered in such a way that it vanishes on the boundary or some line. Using this result one can suppress certain peaks in the probability distribution. The analysis is simplified considerably by choosing a more suitable basis of the coin space, namely the one formed by the eigenvectors of the coin operator.