Clifford Circuit Initialisation for Variational Quantum Algorithms

TL;DR

This paper introduces a Clifford circuit initialisation technique for variational quantum algorithms, improving their performance on intermediate scale quantum computers, especially for quantum chemistry applications.

Contribution

The paper proposes a novel pre-optimisation method using simulated annealing of Clifford parameters to enhance variational quantum algorithms.

Findings

Effective for quantum chemistry problems

Performance depends on Hamiltonian structure and circuit depth

Not arbitrarily scalable, but useful for near-term devices

Abstract

We present an initialisation method for variational quantum algorithms applicable to intermediate scale quantum computers. The method uses simulated annealing of the efficiently simulable Clifford parameter points as a pre-optimisation to find a low energy initial condition. We numerically demonstrate the effectiveness of the technique, and how it depends on Hamiltonian structure, number of qubits and circuit depth. While a range of different problems are considered, we note that the method is particularly useful for quantum chemistry problems. This presented method could help achieve a quantum advantage in noisy or fault-tolerant intermediate scale devices, even though we prove in general that the method is not arbitrarily scalable.