Los Alamos and QC Ware Model Correlated Iron Oxides Using Sample-Based Quantum Diagonalization on IBM Hardware

In a preprint titled Towards Quantum Computation of Bulk FeO, researchers from Los Alamos National Laboratory (LANL) and QC Ware present a hybrid workflow simulating strongly correlated transition metal oxides on quantum processors. Benchmarked on diatomic iron monoxide (FeO) and rhombic iron oxide dimers (Fe₂O₂), the team coupled ab initio-informed d-p tight-binding models with Sample-based Quantum Diagonalization (SQD) on IBM Quantum's ibm_miami system, using near-term hardware purely as a Fock-space sampler to reach chemical accuracy where standalone Variational Quantum Eigensolver (VQE) optimizations stall.

Bulk FeO is an archetypal Mott insulator whose strong electronic correlations cause conventional density functional theory (DFT) to mischaracterize it as metallic. To make these open-shell systems computationally tractable, the authors extracted localized Wannier functions from non-spin-polarized DFT calculations to build multi-orbital d-p Hamiltonians. Variational states were parameterized using a one-layer Local Unitary Cluster Jastrow (LUCJ) ansatz, which restricts two-mode Givens rotations to nearest-neighbor connectivity to eliminate non-local SWAP overheads.

To bypass on-hardware barren plateaus, circuit parameters were optimized in classical statevector simulations and deployed to frozen QPUs strictly for configuration sampling. Measured bitstrings post-selected for particle-number conservation were then expanded into one- and two-shell Fock-space graphs based on non-zero Hamiltonian matrix elements. Classical exact diagonalization of the resulting projected Hamiltonian converged rapidly: two connectivity shells recovered the experimental ⁵Δ_i quintet state for FeO within a compressed subspace of 184 determinants, yielding an excitation energy of 2,167 cm⁻¹ (substantially outperforming prior multireference configuration interaction baselines that predicted 300 cm⁻¹). The methodology establishes a blueprint for modeling bulk periodic FeO by distributing SQD sub-blocks across Brillouin zone k-points.

The preprint is accessible on arXiv here.

October 31, 2026