Multi-QIDA method for VQE state preparation in molecular systems

Abstract

The development of quantum algorithms and their application to quantum chemistry has introduced new opportunities for solving complex molecular problems that are computationally infeasible for classical methods. In quantum chemistry, the Variational Quantum Eigensolver (VQE) is a hybrid quantum-classical algorithm designed to estimate ground-state energies of molecular systems. Despite its promise, VQE faces challenges such as scalability issues, high circuit depths, and barren plateaus that make the optimization of the variational wavefunction. To mitigate these challenges, the Quantum Information Driven Ansatz (QIDA) leverages Quantum Mutual Information (QMI) to construct compact, correlation-driven circuits. In this work, we go back to the original field of application of QIDA, by applying the already defined Multi-Threshold Quantum Information Driven Ansatz (Multi-QIDA) methodology on Molecular Systems. to systematically construct shallow, layered quantum circuits starting from approximate QMI matrices obtained by Quantum Chemistry calculations. The Multi-QIDA approach combines efficient creation of the QMI map, reduction of the number of correlators required by exploiting Minimum/Maximum spanning tress, and an iterative layer-wise VQE optimization routine. These enhancements allow the method to recover missing correlations in molecular systems while maintaining computational efficiency. Additionally, the approach incorporates alternative gate constructions, such as SO(4) correlators, to enhance the circuit expressibility without significantly increasing the circuit complexity. We benchmark Multi-QIDA on systems ranging from small molecules like H2O, BeH2, and NH3 in Iterative Natural Orbitals (INOs) basis set, to active-space models such as H2O-6-31G-CAS(4,4) and N2-cc-pVTZ-CAS(6,6), comparing it to traditional hardware-efficient ansatze.