Backend-sensitive hardware observation of parity-sector and excitation-number correlated decoherence asymmetry in the XY Hamiltonian

This preprint reports a bounded IBM Heron hardware observation of parity-sector and excitation-number correlated decoherence asymmetry in small XY-Hamiltonian circuits. The dynamical Lie algebra of the XY Hamiltonian decomposes under the parity operator, and the experiment measures parity leakage rates across labelled sectors without promoting the observation as a DLA-only causal effect. The archived study uses a 342-circuit campaign on IBM ibm_kingston (Heron r2, 156 qubits), with n = 4 circuits across eight Trotter depths. It reports an odd-sector leakage excess over the even sector, with seven of eight tested depths individually significant under Welch tests, while explicitly treating shared-qubit and shared-calibration context as a boundary on inference. The record includes the manuscript source and PDF for a reproducible archival preprint. Claims are limited to the named hardware campaign, committed raw-count artefacts, stated reducers, and the open repository at https://github.com/anulum/scpn-quantum-control.