Round 2 verification audit for C041

Model: gpt-5

Claim: Single-ion decay (B) is modelled by Kraus operators E_0 = |down>down})|down>up})|up><e|, with the two-ion channel given by the nine maps E_i tensor E_j.

Source alignment: source/supp_content.tex:13-13 (Supp. Mat. S1)

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: Check the single-ion Kraus set is trace-preserving (sum E_k^dag E_k = I on {down,up,e}) given p_{e->down}+p_{e->up}=1.. 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: E0=|d>d)|d>u)|u><e| match the claim. Symbolic (sympy) sum_k E_k^dag E_k = I_3 for general gamma with p_dn=sin^2 g, p_up=cos^2 g (p_dn+p_up=1), proven equal to the identity. Numeric ||sum E^dag E - I_3|| <= 2.2e-16 over a 51-point gamma grid; the nine two-ion maps E_i (x) E_j are also trace-preserving (||sum - I_9|| <= 6.3e-16). Tolerance 1e-12; satisfied. Exact trace-preservation identity -> verified.