Search

Particle production by ultra-strong electric fields is a well-studied research field. Nevertheless, despite repeated attempts to relate the production rate within the field to the formation time of a particle, the latter is still shrouded in mystery. We provide an interpretation of a particle distribution at finite times enabling us to isolate and, therefore, identify the relevant time scales regarding particle formation in quantum physics within and beyond perturbation theory.

We study the enhancement of tunneling through a potential barrier V(x) by a time-dependent electric field with special emphasis on pulse-shaped vector potentials such as A_{x}(t)=A_{0}/cosh^{2}(ωt). In addition to the known effects of preacceleration and potential deformation already present in the adiabatic regime, as well as energy mixing in analogy to the Franz-Keldysh effect in the nonadiabatic (impulse) regime, the pulse A_{x}(t) can enhance tunneling by “pushing” part of the wave function out of the rear end of the barrier. Aside from the natural applications in condensed matter and atomic physics, these findings could be relevant for nuclear fusion, where pulses A_{x}(t) with ω=1keV and peak field strengths of 10^{16}V/m might enhance tunneling rates significantly.

Electron–positron pair production in space- and time-dependent electromagnetic fields is investigated. Especially, the influence of a time-dependent, inhomogeneous magnetic field on the particle momenta and the total particle yield is analyzed for the first time. The role of the Lorentz invariant E2−B2, including its sign and local values, in the pair creation process is emphasized.