Nobody checked which state IBM's flagship quantum chemistry results compute
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- Sample-based quantum diagonalization (SQD) selects electronic configurations from quantum-circuit samples and diagonalizes the Hamiltonian in that subspace.
- The work audits whether SQD calculations on iron–sulfur clusters ([2Fe-2S] and [4Fe-4S]) actually converge to the target spin state (singlet).
- Using a rotation-invariant spin audit, ⟨S²⟩ measurements, and higher spin moments, the analysis finds that no audited execution returns the named singlet at a competitive energy.
- At the largest published dimension, the lowest root is 170 mHa below the published energy but has ⟨S²⟩ = 1.37, far from a singlet, and hardware samples show no advantage over uniform-random control.
- The recommendation is that measured spin moments should become a required benchmark output.
- The archive includes code, data, reproduction maps, and audit trails to reproduce the analysis.