Independent audit finds IBM quantum chemistry benchmarks converged to wrong spin states

A researcher has published an independent audit of IBM's iron–sulfur cluster quantum chemistry results, originally presented in a 2025 Science Advances paper as evidence of practical quantum utility. The audit finds that key calculations converged to incorrect electronic spin states, with measured spin expectation values of 4.7 to 7.0 against a target of zero for a singlet state. When IBM's own archived raw hardware data was run through their own pipeline, the larger iron–sulfur cluster converged to a spin-pure triplet state sitting 1,438 millihartrees from IBM's reference energy. IBM's built-in spin mitigation tool was found to expand the determinant subspace fourfold without actually producing the target singlet state, and a related issue filed on the official Qiskit tracker was closed without the core discrepancy being contested. The audit, which was conducted with AI assistance over roughly 72 hours, includes a full reproduction map linking every claim to verifiable files and commands.