Controlled transport in chiral quantum walks on graphs

• Published in: New journal of physics Vol. 25; no. 8; pp. 83034 - 83051
• Main Authors: Yu, Yi-Cong, Cai, Xiaoming
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01-08-2023
• Subjects: Algorithms; chiral quantum walk; Chirality; directed quantum transport; Efficiency; Graphs; Lattice scattering; Physics; Quantum transport; scattering on lattice; Search algorithms; Symmetry; Transport phenomena; Transport properties; Wave functions; Wave packets; Y junctions; Y-junction graph
• ISSN: 1367-2630; 1367-2630
• DOI: 10.1088/1367-2630/acec90

Abstract
We investigate novel transport properties of chiral continuous-time quantum walks (CTQWs) on graphs. By employing a gauge transformation, we demonstrate that CTQWs on chiral chains are equivalent to those on non-chiral chains, but with additional momenta from initial wave packets. This explains the novel transport phenomenon numerically studied in (Khalique
et al
2021
New J. Phys.
23
083005). Building on this, we delve deeper into the analysis of chiral CTQWs on the Y-junction graph, introducing phases to account for the chirality. The phase plays a key role in controlling both asymmetric transport and directed complete transport among the chains in the Y-junction graph. We systematically analyze these features through a comprehensive examination of the chiral CTQW on a Y-junction graph. Our analysis shows that the CTQW on Y-junction graph can be modeled as a combination of three wave functions, each of which evolves independently on three effective open chains. By constructing a lattice scattering theory, we calculate the phase shift of a wave packet after it interacts with the potential-shifted boundary. Our results demonstrate that the interplay of these phase shifts leads to the observed enhancement and suppression of quantum transport. The explicit condition for directed complete transport or
100
%
efficiency is analytically derived. Our theory has applications in building quantum versions of binary tree search algorithms.