Efficient ground state preparation in variational quantum eigensolver with symmetry-breaking layers

TL;DR

This paper introduces a new quantum circuit ansatz with symmetry-breaking layers that improves ground state preparation efficiency in VQE for systems with symmetry-broken ground states.

Contribution

The paper proposes an alternative ansatz with symmetry-breaking layers, overcoming limitations of the Hamiltonian variational ansatz in symmetry-broken systems.

Findings

The new ansatz finds ground states in shorter depth than HVA.

Numerical simulations confirm improved efficiency for symmetry-broken systems.

The approach enhances VQE performance in complex quantum many-body problems.

Abstract

Variational quantum eigensolver (VQE) solves the ground state problem of a given Hamiltonian by finding the parameters of a quantum circuit ansatz that minimizes the Hamiltonian expectation value. Among possible quantum circuit ans\"{a}tze, the Hamiltonian variational ansatz (HVA) is widely studied for quantum many-body problems as the ansatz with sufficiently large depth is theoretically guaranteed to express the ground state. However, since the HVA shares the same symmetry with the Hamiltonian, it is not necessarily good at finding the symmetry-broken ground states that prevail in nature. In this paper, we systematically explore the limitations of the HVA for solving symmetry-broken systems and propose an alternative quantum circuit ansatz with symmetry-breaking layers. With extensive numerical simulations, we show that the proposed ansatz finds the ground state in depth significantly shorter than the bare HVA when the target Hamiltonian has symmetry-broken ground states.