Improved accuracy on noisy devices by non-unitary Variational Quantum Eigensolver for chemistry applications

TL;DR

This paper introduces nu-VQE, a non-unitary extension of VQE using a Jastrow factor, which improves accuracy and error mitigation on noisy quantum devices for chemistry simulations.

Contribution

The paper presents a novel non-unitary VQE method incorporating a Jastrow factor, enhancing accuracy and noise resilience in quantum chemistry calculations.

Findings

Achieves more accurate ground state energies with shallower circuits.

Significantly reduces energy errors compared to traditional VQE.

Provides effective error mitigation on noisy quantum hardware.

Abstract

We propose a modification of the Variational Quantum Eigensolver algorithm for electronic structure optimization using quantum computers, named non-unitary Variational Quantum Eigensolver (nu-VQE), in which a non-unitary operator is combined with the original system Hamiltonian leading to a new variational problem with a simplified wavefunction Ansatz. In the present work, we use, as non-unitary operator, the Jastrow factor, inspired from classical Quantum Monte Carlo techniques for simulation of strongly correlated electrons. The method is applied to prototypical molecular Hamiltonians for which we obtain accurate ground state energies with shallower circuits, at the cost of an increased number of measurements. Finally, we also show that this method achieves an important error mitigation effect that drastically improves the quality of the results for VQE optimizations on today's noisy quantum computers. The absolute error in the calculated energy within our scheme is one order of magnitude smaller than the corresponding result using traditional VQE methods, with the same circuit depth.