Dissipative ground state preparation in ab initio electronic structure theory

TL;DR

This paper introduces a Lindblad dynamics-based method for efficiently preparing ground states in ab initio electronic structure problems on quantum computers, avoiding variational parameters and addressing non-local Hamiltonians.

Contribution

It proposes two generic types of jump operators for Lindblad dynamics, with proven spectral gap bounds and convergence rates, enabling efficient ground state preparation in complex quantum systems.

Findings

Spectral gap of Lindbladian is lower bounded by a universal constant in simplified models.

Convergence rate for energy and density matrices is universal with Type-I jump operators.

Monte Carlo simulations validate the effectiveness on molecular systems.

Abstract

Dissipative engineering is a powerful tool for quantum state preparation, and has drawn significant attention in quantum algorithms and quantum many-body physics in recent years. In this work, we introduce a novel approach using the Lindblad dynamics to efficiently prepare the ground state for general ab initio electronic structure problems on quantum computers, without variational parameters. These problems often involve Hamiltonians that lack geometric locality or sparsity structures, which we address by proposing two generic types of jump operators for the Lindblad dynamics. Type-I jump operators break the particle number symmetry and should be simulated in the Fock space. Type-II jump operators preserves the particle number symmetry and can be simulated more efficiently in the full configuration interaction space. For both types of jump operators, we prove that in a simplified Hartree-Fock framework, the spectral gap of our Lindbladian is lower bounded by a universal constant. For physical observables such as energy and reduced density matrices, the convergence rate of our Lindblad dynamics with Type-I jump operators remains universal, while the convergence rate with Type-II jump operators only depends on coarse grained information such as the number of orbitals and the number of electrons. To validate our approach, we employ a Monte Carlo trajectory-based algorithm for simulating the Lindblad dynamics for full ab initio Hamiltonians, demonstrating its effectiveness on molecular systems amenable to exact wavefunction treatment.