Structural Protection of GHZ States: Definitive Cross-Platform Validation Across Five Quantum Processors (v4.0)

Version 4.0: Definitive experimental validation of structural coherence protection (N2) in GHZ entangled states across five quantum computing platforms. KEY RESULTS:- IonQ Forte: +7.27% GHZ advantage over product states (p = 7.17×10⁻²⁷, Cohen's d = 6.11)- IBM Heron: 2.4–13.8× slower decay for GHZ vs product states- Rigetti Ankaa-3, IQM Garnet, IQM Emerald: No N2 detected (negative controls) MAIN FINDINGS:1. N2 is real and statistically incontrovertible (p 99.5% 2Q gate fidelity threshold4. N2 is GHZ-specific: W-states and Cluster states show no protection5. Negative results on Rigetti/IQM provide mechanistic insight into fidelity thresholds PLATFORMS TESTED:- IBM Heron (ibm_torino, ibm_fez, ibm_boston)- IonQ Forte 1 (trapped ions, 36 qubits)- Rigetti Ankaa-3 (84 qubits)- IQM Garnet (20 qubits)- IQM Emerald (5 qubits) Total experimental investment: ~$3,700 USD This version incorporates Panel Cerezo methodology recommendations and extends v3.1 (DOI: 10.5281/zenodo.18291164) with definitive statistical analysis meeting all rigor criteria. Experiment dates: January 15-19, 2026