Classical reservoir approach for efficient molecular ground state preparation

TL;DR

The paper introduces a classical reservoir variational ansatz for quantum ground state preparation that is hardware-efficient, operates in localized orbitals, and achieves chemical accuracy with reduced circuit depths across various molecular systems.

Contribution

A novel classical reservoir approach tailored for near-term quantum hardware, enabling efficient and accurate molecular ground state calculations with minimal circuit complexity.

Findings

Achieves chemical accuracy for diverse molecules and bond lengths.

Reduces circuit depth when relaxed error thresholds are used.

Successfully benchmarks on molecules up to an effective 24 qubits.

Abstract

Ground state preparation is a central application of quantum algorithms for electronic structure. We introduce the classical reservoir approach, a low cost variational ansatz tailored to near-term hardware, requiring only nearest-neighbor interactions on a machine with square-lattice connectivity. Unlike traditional methods built from the classically efficient Hartree Fock theory, our ansatz operates in localized molecular orbitals to study previously unexplored regions of the variational parameter space. Numerical benchmarks demonstrate chemical accuracy across diverse systems and bond lengths; notably, significantly reduced circuit depths are attainable when relaxed error thresholds (e.g., tens of E_h) are permissible. We benchmark the method on hydrogen chains, N_2, O_2, CO, BeH_2, and H_2O, the latter corresponding to an effective 24 qubit calculation.