Spatially dependent electron-positron pair creation rate

Abstract

The vacuum breakdown process in an inhomogeneous supercritical electric field of finite extension is examined. By probing the electron-positron pair creation zone with incoming electrons that have controlled velocities, we can address the fundamental question of where the electrons are being created from the vacuum. In contrast to what one might expect, the spatial regions of most likely pair creation are not necessarily those where the electric-field strength is largest. In fact, the creation regions are determined solely by energetic considerations and particles can therefore be created in spatial regions where the local field strength is far below the Schwinger threshold. These predictions are also supported independently by spatial probability densities obtained by extrapolation as well as by classical and quantum-mechanical analysis.