The physics of adiabatic particle number in the Schwinger effect

TL;DR

This paper clarifies the physical meaning of the adiabatic particle number in the Schwinger effect, showing it can be unambiguously interpreted and that large, transient pair numbers are physically meaningful.

Contribution

It provides a clear interpretation of the adiabatic particle number, resolving ambiguities and demonstrating its physical relevance during non-asymptotic times.

Findings

Adiabatic particle number has an unambiguous, physical interpretation.

Large pair numbers at non-asymptotic times are physically accessible.

Clarification of what is being counted in pair production.

Abstract

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