Gate-efficient simulation of molecular eigenstates on a quantum computer

TL;DR

This paper demonstrates a gate-efficient quantum algorithm for simulating molecular eigenstates on near-term superconducting quantum hardware, utilizing exchange-type gates to reduce circuit depth and improve accuracy within coherence time constraints.

Contribution

The study experimentally implements a variational algorithm using exchange-type gates on superconducting qubits, achieving high fidelity and accurate molecular eigenstate computations.

Findings

Exchange-type gates preserve excitation number, reducing circuit complexity.

Achieved 95% gate fidelity with superconducting qubits.

Computed molecular hydrogen eigenstates with 50 mHartree accuracy.

Abstract

A key requirement to perform simulations of large quantum systems on near-term quantum hardware is the design of quantum algorithms with short circuit depth that finish within the available coherence time. A way to stay within the limits of coherence is to reduce the number of gates by implementing a gate set that matches the requirements of the specific algorithm of interest directly in hardware. Here, we show that exchange-type gates are a promising choice for simulating molecular eigenstates on near-term quantum devices since these gates preserve the number of excitations in the system. Complementing the theoretical work by Barkoutsos et al. [PRA 98, 022322 (2018)], we report on the experimental implementation of a variational algorithm on a superconducting qubit platform to compute the eigenstate energies of molecular hydrogen. We utilize a parametrically driven tunable coupler to realize exchange-type gates that are configurable in amplitude and phase on two fixed-frequency superconducting qubits. With gate fidelities around 95% we are able to compute the eigenstates within an accuracy of 50 mHartree on average, a limit set by the coherence time of the tunable coupler.