Cross-Simulator Parity Validation of Quantum Network Entanglement Swapping: A Pre-Declared Validation Methodology with Two Independent Discrete-Event Simulators

Abstract

We report three principal findings. First, two independent discrete-event quantum-network simulators—NetSquid 1.1.8 and SeQUeNCe 1.2.0—agree with an analytical Werner-swap oracle and with each other to machine precision in 160/160 state-level cases (max |ΔF| = 8.88×10−16) and in 50/50 protocol-level cases under matched source, channel, detector, heralding, retry, cutoff, BSM, readout, occupancy, latency, and goodput semantics. Second, when the shared harness is released and each simulator runs its own asynchronous event engine with independent random streams, mean output fidelity can be equivalent while the fidelity distributions differ strongly (Kolmogorov–Smirnov p≈10−27); a systematic timestamp-replay diagnosis localises this discrepancy to control/timing sampling rather than quantum-kernel disagreement. Third, a lightweight simulator (QMRB v0.2) with an incorrect Werner swap cross-term (/9 instead of /3) passes all counter-level parity checks but fails all 80 repeater fidelity comparisons with a mean error of 0.0235, demonstrating that modelform errors can be invisible at the counter level and silent until a fidelity threshold is crossed. To obtain these results we introduce a layered, pre-declared validation methodology comprising four layers: state-level parity, protocol-level parity, native-event parity, and model-form diagnosis. Each layer has an acceptance criterion frozen before execution. The methodology distinguishes implementation parity from model-form parity and from protocollevel parity, and reports explicit boundaries on what each layer does and does not establish.