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.
Highlights
One of the most well-known nonperturbative predictions of quantum electrodynamics is the Schwinger effect, the creation of electron-positron pairs from light [1,2]
Even the most common and wellknown choice, that of a basis of adiabatic Hamiltonian eigenstates, yields pair numbers which fluctuate wildly in time and can exhibit transient values orders of magnitude higher than the final, unambiguous, number of pairs. This has led to drastic overestimates for the number of pairs which could be created in experiments, and as such it is repeatedly emphasized that no direct physical meaning
Our aim in this paper is to motivate a change in perspective: rather than asking which of the infinitely many bases is physically relevant for pair production, we will here turn the question around and ask instead what is the physics contained in different bases? We suggest that this may be the more physically relevant, and revealing, question
Summary
One of the most well-known nonperturbative predictions of quantum electrodynamics is the Schwinger effect, the creation of electron-positron pairs from light [1,2]. Even the most common and wellknown choice, that of a basis of adiabatic Hamiltonian eigenstates, yields pair numbers which fluctuate wildly in time and can exhibit transient values orders of magnitude higher than the final, unambiguous, number of pairs. This has led to drastic overestimates for the number of pairs which could be created in experiments, and as such it is repeatedly emphasized that no direct physical meaning. We will work throughout with time-dependent but spatially homogeneous fields; while these are not directly relevant to future (e.g. laser) experiments, they are the prototype example used in the study of nonperturbative pair production, beyond the completely constant case.
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