Efficient Operator Selection and Warm-Start Strategy for Excitations in Variational Quantum Eigensolvers

TL;DR

This paper introduces a new, efficient method for preparing electronic ground states in quantum chemistry using optimized operator selection and warm-start strategies, achieving quadratic speedup over existing methods.

Contribution

It combines ExcitationSolve with variational quantum eigensolver techniques to reduce complexity and CNOT operations, enabling faster convergence in ground state preparation.

Findings

Quadratic convergence speedup observed

Reduced CNOT gate count in experiments

Efficient classical pre-processing for operator selection

Abstract

We present a novel approach for efficient preparation of electronic ground states, leveraging the optimizer ExcitationSolve [J\"ager et al., Comm. Phys. (2025)] and established variational quantum eigensolver-based operator selection methods, such as Energy Sorting. By combining these tools, we demonstrate a computationally efficient protocol that enables the construction of an approximate ground state from a unitary coupled cluster ansatz via a single sweep over the operator pool. Utilizing efficient classical pre-processing to select the majority of relevant operators, this approach reduces the computational complexity associated with traditional optimization methods. Furthermore, we show that this method can be seamlessly integrated with one-variational-parameter couple exchange operators, thereby further reducing the number of required CNOT operations. Overall, we empirically observe a quadratic convergence speedup beyond state-of-the-art methods, advancing the realization of quantum advantage in quantum chemistry.