Relativistic VQE calculations of molecular electric dipole moments on trapped ion quantum hardware

TL;DR

This paper demonstrates high-precision relativistic VQE calculations of molecular electric dipole moments on quantum hardware, employing resource reduction and error mitigation techniques to achieve accurate results on noisy intermediate-scale quantum devices.

Contribution

It introduces methods to perform relativistic VQE calculations of electric dipole moments with reduced quantum resources and improved accuracy on current quantum hardware.

Findings

Achieved 99.71% reduction in two-qubit gates for 12-qubit circuits.

Error in PDM on hardware is -1.17% relative to classical calculations.

Successfully computed PDMs for molecules on IonQ quantum devices with high precision.

Abstract

The quantum-classical hybrid variational quantum eigensolver (VQE) algorithm is among the most actively studied topics in atomic and molecular calculations on quantum computers, yet few studies address properties other than energies or account for relativistic effects. This work presents high-precision 18-qubit relativistic VQE simulations for calculating the permanent electric dipole moments (PDMs) of BeH to RaH molecules on traditional computers, and 6- and 12-qubit PDM computations for SrH on IonQ quantum devices. To achieve high precision on current noisy intermediate scale era quantum hardware, we apply various resource reduction methods, including Reinforcement Learning and causal flow preserving ZX-Calculus routines, along with error mitigation and post-selection techniques. Our approach reduces the two-qubit gate count in our 12-qubit circuit by 99.71%, with only a 2.35% trade-off in precision for PDM when evaluated classically within a suitably chosen active space. On the current generation IonQ Forte-I hardware, the error in PDM is -1.17% relative to classical calculations and only 1.21% compared to the unoptimized circuit.