The calibration epoch as the unit of evidence: preregistered parity-leakage and layout-transfer experiments on IQM Garnet

We report five preregistered experiments on the IQM Garnet 20-qubit square-lattice processor, each with its decision rule committed before any hardware data existed and each reported regardless of outcome. First, the even-over-odd parity-sector leakage asymmetry previously measured on IBM Heron r2 replicates on Garnet at preregistered power (relative asymmetry +0.068, one-sided p = 1.1 × 10−5). Because the noiseless parity leakage of these number-conserving XY-Trotter circuits is exactly zero, this is a statement about device noise. Second, the asymmetry is not stable: over ten execution windows it varies beyond shot noise at fixed depth (Cochran Q = 19.01 on 9 degrees of freedom, p = 0.025), more strongly when windows are pooled by provider calibration set (p = 0.0083), and an isolated sign reversal at depth 10 does not replicate. Third, a confirmatory campaign that takes the calibration epoch as its independent unit — twelve epochs, 688,128 shots — finds the asymmetry larger at depth 8 than at depth 12 (mean contrast +0.0173, one-sided p = 0.026); the lower bound is +0.0030 and three of twelve epochs have the opposite sign. Fourth, a calibration-aware layout optimiser developed on heavy-hex devices fails its frozen transfer rule: it is better than automatic placement at chain lengths 8 and 16 and worse at 12, and a powered follow-up confirms the reversal. All preregistrations, calibration snapshots, job identifiers, raw counts and analysis scripts are public. All quantum-hardware results were obtained on IQM Garnet through IQM Resonance under an extended-access research grant. Preregistrations, raw counts and analysis code: https://github.com/anulum/scpn-quantum-control