# Quantum Chemistry as a Benchmark for Near-Term Quantum Computers

## TL;DR

This paper introduces a quantum chemistry benchmark for near-term quantum computers using variational algorithms, error mitigation, and active space reduction, demonstrating improved accuracy and providing a baseline for hardware comparison.

## Contribution

It develops a comprehensive quantum chemistry benchmark suite tailored for noisy intermediate-scale quantum devices, incorporating novel error mitigation and active space techniques.

## Key findings

- Achieved chemical accuracy on certain quantum hardware for specific molecular systems.
- Demonstrated the effectiveness of McWeeny purification in error mitigation.
- Provided a baseline for hardware performance comparison in quantum chemistry simulations.

## Abstract

We present a quantum chemistry benchmark for noisy intermediate-scale quantum computers that leverages the variational quantum eigensolver, active space reduction, a reduced unitary coupled cluster ansatz, and reduced density purification as error mitigation. We demonstrate this benchmark on the 20 qubit IBM Tokyo and 16 qubit Rigetti Aspen processors via the simulation of alkali metal hydrides (NaH, KH, RbH),with accuracy of the computed ground state energy serving as the primary benchmark metric. We further parameterize this benchmark suite on the trial circuit type, the level of symmetry reduction, and error mitigation strategies. Our results demonstrate the characteristically high noise level present in near-term superconducting hardware, but provide a relevant baseline for future improvement of the underlying hardware, and a means for comparison across near-term hardware types. We also demonstrate how to reduce the noise in post processing with specific error mitigation techniques. Particularly, the adaptation of McWeeny purification of noisy density matrices dramatically improves accuracy of quantum computations, which, along with adjustable active space, significantly extends the range of accessible molecular systems. We demonstrate that for specific benchmark settings, the accuracy metric can reach chemical accuracy when computing over the cloud on certain quantum computers.