Quantum search algorithms on a regular lattice

TL;DR

This paper analyzes quantum search algorithms on d-dimensional lattices, providing approximations for search time and localization probability, and explicitly calculating key coefficients for dimensions two and three.

Contribution

It offers a new perspective on lattice search algorithms through level dynamics near avoided crossings, with explicit calculations for multiple dimensions.

Findings

Derived approximations for level-splitting and subspace dynamics.

Provided explicit coefficients for d=2 and d=3.

Presented closed-form expressions for higher dimensions.

Abstract

Quantum algorithms for searching one or more marked items on a d-dimensional lattice provide an extension of Grover's search algorithm including a spatial component. We demonstrate that these lattice search algorithms can be viewed in terms of the level dynamics near an avoided crossing of a one-parameter family of quantum random walks. We give approximations for both the level-splitting at the avoided crossing and the effectively two-dimensional subspace of the full Hilbert space spanning the level crossing. This makes it possible to give the leading order behaviour for the search time and the localisation probability in the limit of large lattice size including the leading order coefficients. For d=2 and d=3, these coefficients are calculated explicitly. Closed form expressions are given for higher dimensions.