Symmetry-noise interplay in quantum walk on an n-cycle

TL;DR

This paper investigates how symmetry properties of quantum walks on an n-cycle are affected by noise, revealing that noise can restore certain symmetries and serve as a probe of walk topology.

Contribution

It demonstrates that symmetry breaking in quantum walks on an n-cycle can be used to probe topology and shows how noise influences symmetry restoration.

Findings

Symmetry is preserved in quantum walks on a line but breaks down on an n-cycle.

Noise can restore symmetry by classicalizing the walk.

Noise desensitizes the symmetry operation to the walk topology.

Abstract

Augmenting the unitary transformation which generates a quantum walk by a generalized phase gate G is a symmetry for both noisy and noiseless quantum walk on a line, in the sense that it leaves the position probability distribution invariant. However, this symmetry breaks down in the case of a quantum walk on an n-cycle, and hence can be regarded as a probe of the walk topology. Noise, modelled here as phase flip and generalized amplitude damping channels, tends to restore the symmetry because it classicalizes the walk. However, symmetry restoration happens even in the regime where the walker is not entirely classical, because noise also has the effect of desensitizing the operation G to the walk topology. We discuss methods for physical implementation, and talk about the wider implications to condensed matter systems.