Physics of adiabatic particle number in the Schwinger effect

The production of electron-positron pairs from light is a famous prediction quantum electrodynamics. Yet it often emphasized that the number produced has no physical meaning until driving electromagnetic fields are switched off, as otherwise its definition basis dependent. common adiabatic definition, in particular, can predict ``creation'' orders magnitude larger than final yield. We show here, by clarifying exactly what being counted, an unambiguous and interpretation. As result, perhaps contrary to expectation, large numbers seen at nonasymptotic times become, principle, physically accessible.