On models of nonlinear evolution paths in adiabatic quantum algorithms

TL;DR

This paper compares two nonlinear adiabatic quantum evolution models for search problems, revealing their limitations based on initial state overlap and providing theorems explaining why they do not outperform standard methods in certain cases.

Contribution

It introduces and analyzes two nonlinear evolution models in adiabatic quantum algorithms, highlighting their limitations and providing theoretical explanations for their performance.

Findings

Both models offer constant speedup when initial and final states overlap.

One model fails with zero overlap, leading to infinite complexity.

Theorems explain why neither model surpasses traditional adiabatic algorithms in certain scenarios.

Abstract

In this paper, we study two different nonlinear interpolating paths in adiabatic evolution algorithms for solving a particular class of quantum search problems where both the initial and final Hamiltonian are one-dimensional projector Hamiltonians on the corresponding ground state. If the overlap between the initial state and final state of the quantum system is not equal to zero, both of these models can provide a constant time speedup over the usual adiabatic algorithms by increasing some another corresponding "complexity". But when the initial state has a zero overlap with the solution state in the problem, the second model leads to an infinite time complexity of the algorithm for whatever interpolating functions being applied while the first one can still provide a constant running time. However, inspired by a related reference, a variant of the first model can be constructed which also fails for the problem when the overlap is exactly equal to zero if we want to make up the "intrinsic" fault of the second model-an increase in energy. Two concrete theorems are given to serve as explanations why neither of these two models can improve the usual adiabatic evolution algorithms for the phenomenon above. These just tell us what should be noted when using certain nonlinear evolution paths in adiabatic quantum algorithms for some special kind of problems.