Enhancement of electron-positron pair creation due to transient excitation of field-induced bound states

We study the creation of electron-positron pairs induced by two spatially separated electric fields that vary periodically in time. The results are based on large-scale computer simulations of the time-dependent Dirac equation in reduced spatial dimensions. When the separation of the fields is very large, the pair creation is caused by multiphoton transitions and mainly determined by the frequency of the fields. However, for small spatial separations a coherence effect can be observed that can enhance or reduce the particle yield compared to the case of two infinitely separated fields. If the travel time for a created electron or positron between both field locations becomes comparable to the period of the oscillating fields, we observe peaks in the energy spectrum which can be explained in terms of field-induced transient bound states.