Bounded Drift Before Error Correction: Why Long-Run Quantrum Execution Fails without Preventive Phase Stabilization

Abstract Long-run quantum execution remains fundamentally constrained, not primarily by gate infidelity, but by cumulative instability of the rotating phase reference during runtime. While contemporary quantum control stacks rely on calibration, dynamical decoupling, and quantum error correction, these mechanisms operate reactively and assume that the underlying phase frame remains valid between interventions. This assumption breaks down as execution depth, runtime, and system size increase. This note reframes long-run execution failure as a phase-frame stability problem rather than a post-fault correction problem. Using empirical hardware-adjacent observations, it shows that longitudinal drift is structured, temporally correlated, and often collective across qubits, placing it outside the effective bandwidth of fast-noise suppression techniques. As a result, computation is frequently admitted under metastable conditions in which logical error amplification occurs despite unchanged physical gate metrics. Based on this empirical and structural analysis, the note identifies a missing architectural element: a preventive drift-bounding layer that constrains phase-frame deviation before execution proceeds. The argument is intentionally architectural rather than implementational. No hardware-specific parameters, algorithms, or corrective primitives are disclosed. The purpose of this document is to establish why scalable quantum execution requires preventive phase stabilization at the execution boundary, and why reactive correction alone cannot remove this limitation. Detailed theoretical foundations, validation pathways, and hardware-compatible realizations exist but are intentionally excluded from this public note.