Microcanonical and finite temperature ab initio molecular dynamics simulations on quantum computers

TL;DR

This paper explores the use of variational quantum algorithms for ab initio molecular dynamics, addressing noise mitigation and demonstrating simulations of simple molecules on quantum hardware for microcanonical and canonical ensembles.

Contribution

It introduces noise mitigation schemes for quantum AIMD and proposes a Langevin dynamics algorithm for finite temperature simulations on quantum computers.

Findings

Reliable MD trajectories achieved despite potential energy errors

Algorithms successfully applied to H2 and H3+ molecules

Demonstrated quantum simulation of H2 dynamics on IBM quantum hardware

Abstract

Ab initio molecular dynamics (AIMD) is a powerful tool to predict properties of molecular and condensed matter systems. The quality of this procedure is based on accurate electronic structure calculations. The development of quantum processors has shown great potential for the efficient evaluation of accurate ground and excited state energies of molecular systems, opening up new avenues for molecular dynamics simulations. In this work we address the use of variational quantum algorithms for the calculation of accurate atomic forces to be used in AIMD. In particular, we provide solutions for the alleviation of the statistical noise associated to the measurements of the expectation values of energies and forces, as well as schemes for the mitigation of the hardware noise sources (in particular, gate infidelities, qubit decoherence and readout errors). Despite the relative large error in the calculation of the potential energy, our results show that the proposed algorithms can provide reliable MD trajectories in the microcanonical (constant energy) ensemble. Further, exploiting the intrinsic noise arising from the quantum measurement process, we also propose a Langevin dynamics algorithm for the simulation of canonical, i.e., constant temperature, dynamics. Both algorithms (microcanonical and canonical) are applied to the simulation of simple molecular systems such as H2 and H3+. Finally, we also provide results for the dynamics of H2 obtained with IBM quantum computer ibmq_athens.