Subspace Variational Quantum Simulator

TL;DR

The paper introduces the subspace variational quantum simulator (SVQS), a method for efficient quantum dynamics simulation on NISQ devices that leverages subspace search to reduce overhead and accurately mimic low-energy molecular processes.

Contribution

It presents SVQS, a novel approach combining subspace search with variational algorithms to simulate quantum dynamics efficiently on NISQ hardware.

Findings

Successfully simulated hydrogen molecule dynamics

Achieved subspace process fidelity of 0.88-0.98

Reduced overhead compared to existing schemes

Abstract

Quantum simulation is one of the key applications of quantum computing, which accelerates research and development in the fields such as chemistry and material science. The recent development of noisy intermediate-scale quantum (NISQ) devices urges the exploration of applications without the necessity of quantum error correction. In this paper, we propose an efficient method to simulate quantum dynamics driven by a static Hamiltonian on NISQ devices, named subspace variational quantum simulator (SVQS). SVQS employs the subspace-search variational quantum eigensolver (SSVQE) to find a low-lying eigensubspace and extends it to simulate dynamics within the subspace with lower overhead compared to the existing schemes. We experimentally simulate the time-evolution operator in a low-lying eigensubspace of a hydrogen molecule. We also define the subspace process fidelity as a measure between two quantum processes in a subspace. The subspace time evolution mimicked by SVQS shows the subspace process fidelity of $0.88$-$0.98$.