Ansätze for Noisy Variational Quantum Eigensolvers

Abstract

The hardware requirements of useful quantum algorithms remain unmet by the quantum computers available today. Because it was designed to soften these requirements, the Variational Quantum Eigensolver (VQE) has gained popularity as a contender for a chance at quantum advantage with near-term quantum computers. The ansatz, a parameterized circuit that prepares trial states, can dictate the success (or lack thereof) of a VQE. Too deep ansätze can hinder near-term viability, or lead to trainability issues that render the algorithm inefficient. The purpose of this thesis was to analyse different ansätze proposed for quantum chemistry, examining their noise-resilience and viability in state-of-the-art quantum computers. In particular, dynamic ansätze (ADAPT-VQEs) were explored, and the impact of the choice of pool and selection criterion on their performance was analysed.

196 pages, 62 figures. Thesis submitted for the degree of Master of Science in the Engineering Physics course at University of Minho