Spin audit of SQD/QSCI quantum-chemistry benchmarks on iron–sulfur clusters

IBM's iron–sulfur SQD results have been disputed, with a critique arguing that quantum samples never beat classical selected-CI at matched cost. An engineer measured the electronic state of these calculations and found that they converge to a different state than the target singlet. IBM ships a mitigation for this issue, but it does not produce a singlet state. The engineer filed a bug report on this issue, and a maintainer responded, explaining that the flag used in the mitigation augments the sampled subspace, not the spin state. Running IBM's raw hardware measurement records through their pipeline shows that the results are still off.