Continuous-time quantum walks on a defective lattice: boosting the spreading of delocalized states through Parrondo's strategy

TL;DR

This paper demonstrates that introducing complex-phase defects and alternating defect configurations in continuous-time quantum walks on a lattice can significantly enhance quantum transport, illustrating a quantum version of Parrondo's paradox.

Contribution

It reveals that single complex-phase defects and time-dependent defect protocols can boost quantum transport, providing new methods for controlling quantum walks.

Findings

Single defect enhances ballistic spreading

Alternating defect configurations improve transport efficiency

Manifestation of Parrondo's paradox in quantum walks

Abstract

We investigate the quantum transport of delocalized states in continuous-time quantum walks (CTQWs) on a one-dimensional lattice containing a single defect. The defect is modeled by assigning complex-valued hopping amplitudes to the edges that connect the site corresponding to the mean position of the initial delocalized state to its nearest neighbors. We find that this single defective site is sufficient to enhance the ballistic spreading of an initially Gaussian wave packet. Extending these results, we implement a time-dependent alternation protocol between two distinct defect configurations, each individually yielding poor propagation of the state. The combination of these two unfavorable configurations improves the transport efficiency of the quantum walker, revealing a manifestation of Parrondo's paradox in CTQWs with delocalized initial states. This study provides new insights into the role of complex-phase defects and time-dependent protocols in CTQWs, demonstrating that the interplay between quantum interference and graph engineering can effectively enhance quantum transport in discrete lattices.