Comparative Coherence Decay of GHZ, W, and Product States Under Idle Noise in IBM Heron Quantum Processors: Extended Analysis with Dynamical Decoupling

Version 2.1: Extended experimental analysis comparing coherence decay of GHZ, W, and product states on IBM Heron quantum processors (r1, r2, r3). Key findings:- GHZ states decay 2.4–13.8× slower than product states across three processor generations- Dynamical decoupling with virtual Z-pulses (DD-Z) provides marginal improvement (+0.6%), while physical X-pulses (DD-X) degrade coherence by -24.4%- W-state performance is architecture-dependent: superior on r1/r3, inferior on r2- Weak non-Markovian noise signatures detected at 5 µs delay window This version extends v1.0 (DOI: 10.5281/zenodo.18274447) with W-state analysis, comprehensive DD protocol testing, and the DD-Z vs DD-X discovery. Backends: ibm_torino (r1), ibm_fez (r2), ibm_boston (r3)Configuration: 3-5 qubits, 4000 shots, delays 0-100,000 dt