Round 2 verification audit for C023

Model: gpt-5

Claim: All errors of drive (A) (with |up> spectroscopically decoupled) can be described through 16 elementary error channels {I_e,X_e,Y_e,Z_e}^{tensor 2} acting on the {|down>,|e>}^{tensor 2} subspace.

Source alignment: source/main.tex:138-138 (Theoretical error analysis)

Prior official verdict: verified with failure_reason None.

Executable evidence: run.py. Sandbox rerun logs: run.log.

Independent audit: I scanned the copied script for imports/shared helper dependencies and reran it through the sandbox. The code is self-contained in this attempt directory and targets the claim strategy: Confirm the two-qubit Pauli basis on the {|down>,|e>} subspace has 16 elements and matches the M_{i,j} operators defined in Supp. Mat. S2.. I checked the relevant family model rather than relying only on exit status; the rerun is treated as one reproducibility input.

Decision: Round 2 verdict is verified with failure_reason None and limitations []. Notes: {I,X,Y,Z} on the {down,e} qubit form a complete Hilbert-Schmidt-orthogonal operator basis (single-ion Gram = 2I_4; Pauli algebra X^2=Y^2=Z^2=I, XY=iZ all hold). The 16 tensor products {I_e,X_e,Y_e,Z_e}^{otimes2} have rank 16 and Gram = 4I_16, so they span the full 16-dim operator space on {down,e}^{otimes2}. Hence every error restricted to that subspace (|up> decoupled) is a combination of these 16 elementary channels. Clean mathematical fact -> verified.