Measurements as a roadblock to near-term practical quantum advantage in chemistry: resource analysis

TL;DR

This paper analyzes the resource requirements of VQE for quantum chemistry, showing that current improvements are insufficient for practical quantum advantage and highlighting the need for novel operator estimation methods.

Contribution

The study provides an exhaustive resource analysis for VQE in chemistry, demonstrating the limitations of existing techniques for achieving quantum advantage.

Findings

VQE requires an impractical number of measurements for small molecules.

Modern improvements like low-rank Hamiltonian factorizations are insufficient.

Novel operator estimation methods may be necessary for quantum advantage.

Abstract

Recent advances in quantum computing devices have brought attention to hybrid quantum-classical algorithms like the Variational Quantum Eigensolver (VQE) as a potential route to practical quantum advantage in chemistry. However, it is not yet clear whether such algorithms, even in the absence of device error, could actually achieve quantum advantage for systems of practical interest. We have performed an exhaustive analysis to estimate the number of qubits and number of measurements required to compute the combustion energies of small organic molecules and related systems to within chemical accuracy of experimental values using VQE. We consider several key modern improvements to VQE, including low-rank factorizations of the Hamiltonian. Our results indicate that although these techniques are useful, they will not be sufficient to achieve practical quantum computational advantage for our molecular set, or for similar molecules. This suggests that novel approaches to operator estimation leveraging quantum coherence, such as Enhanced Likelihood Functions [arxiv:2006.09350, arxiv:2006.09349], may be required.