Robust quantum state engineering through coherent localization in biased-coin quantum walks

TL;DR

This paper demonstrates a robust method for quantum state engineering using biased-coin quantum walks, leveraging coherent localization and post-selection to create large superpositions of position states, with practical optical implementation.

Contribution

It introduces a new protocol for generating large non-classical position states via biased quantum walks, resilient to noise and parameter variations.

Findings

Protocol achieves large superpositions through coherent localization.

Method is robust against noise and parameter fluctuations.

Feasible optical implementation demonstrated.

Abstract

We address the performance of a coin-biased quantum walk as a generator for non-classical position states of the walker. We exploit a phenomenon of coherent localisation in the position space --- resulting from the choice of small values of the coin parameter and assisted by post-selection --- to engineer large-size coherent superpositions of distinguishable position states of the walker. The protocol that we design appears to be remarkably robust against both the actual value taken by the coin parameter and strong dephasing-like noise acting on the spatial degree of freedom. We finally illustrate a possible linear-optics implementation of our proposal, suitable for both bulk and integrated-optics platforms.