Diffraction at a time grating in electron-positron pair creation from the vacuum

Abstract

The Sauter-Schwinger process of electron-positron pair creation from the vacuum, driven by a sequence of time-dependent electric-field pulses, is studied in the framework of the quantum-field theoretical approach. As demonstrated by our numerical results, the momentum distributions of produced pairs exhibit intra- and interpulse interference structures. We show that such structures can be observed beyond the regime of applicability of the Wentzel-Kramers-Brillouin theory, which was the focus of earlier investigations. Going beyond these developments, we perform the analysis of the time-evolution operator for an arbitrary eigenmode of the fermionic field. This shows that a perfect coherent enhancement of the interpulse peaks can never be reached. A nearly perfect coherence, on the other hand, is due to nonadiabatic transitions at avoided crossings of the phases defining the unitary time evolution. This analysis allows us to determine the conditions under which the nearly perfect coherence is lost.