Study On The Creation Of Electron And Positron Pairs In Vacuum With Strong Electric Fields

With the rapid development of laser technology,the generation process of electron and positron in vacuum under high intensity laser field,that is,the topic of "light into matter" has gradually become a interesting topic.Quantum electrodynamics is one of the most mature branches of quantum field theory.With the development and establishment of QED and QFT,scientists have theorized many formulas for how to create pairs of positive and negative particles in a vacuum.Moreover,quantum field theory is widely regarded as one of the most fundamental physical disciplines describing the world.Therefore,on the theoretical basis of quantum electrodynamics,by solving the Dirac equation,K-G equation,etc.,and conducting numerical simulation to carry out scientific research,we can realize the observation and mastery of electron-positron pairs generated in vacuum.This thesis mainly includes the following studies.The electron-positron pair creation from a vacuum in an oscillating potential with multiple well-barrier structures is investigated by the computational quantum field theory.For the potential with a well-barrier structure,it is found that when the distance between the well and barrier is large,the pair yield is only double of that in a single oscillating potential well.However,when the distance is small,the pair yield is much larger than the sum of the pairs created individually by the tunneling mechanism and by the photon absorption regime.This result is also analyzed by the energy spectrum of created pairs.Furthermore,for the potential with multiple well-barrier structures,it is discovered that pair creation process can be further enhanced by increasing the number of well-barrier structures.This designed field may be used to create observable pairs in the laboratory.The momentum spectrum and the number density of created electron-positron pairs in a frequency modulated laser field are investigated using the quantum kinetic equation.It is found that the momentum spectrum presents an obvious interference pattern.This is an imprint of the frequency modulated field on the momentum spectrum,because the momentum peaks correspond to the pair production process by absorbing different frequency component photons.Moreover,the interference effect can also be understood qualitatively by analyzing turning-point structures.The study of the pair number density shows that the number density is very sensitive to modulation parameters and can be enhanced by 2 or 3 orders of magnitude for certain modulation parameters,which may provide a new way to increase the number of created electron-positron pairs in future experiments.We study the dynamical response of the Dirac vacuum state to a very strong time-dependent electric field pulse,whose frequency is chirped in time.The resulting field-induced electron-positron pair-creation process can be used to examine various proposals for time-dependent frequency spectra of the external field.It turns out that the Dirac vacuum can be used as sensitive probe that can respond to the instantaneous values of the frequency at each moment of time by producing electrons with a characteristic energy.This almost instantaneous response feature of the vacuum state permits us to introduce a generalized rate equation.It is based on the concept of a time-dependent decay rate and can provide semianalytical solutions to predict the number of created electron-positron pairs during the interaction with arbitrarily chirped electric field pulses.We examine the effect of a frequency-chirped external force field on the final energy that has been absorbed by two classical mechanical oscillators,by quantum mechanical two-and three-level systems,and by electron-positron pairs that were created from the quantum field theoretical Dirac vacuum.By comparing the final dynamical responses to the original force field with that associated with the corresponding time-reversed field,we can test the sensitivity of each of these five systems to the temporal phase information contained in the field.We predict that the linear oscillator,the two-level atom,and the pair-creation process triggered by a spatially homogeneous field are remarkably immune to this phase,whereas the quartic oscillator,the three-level atom,or the pair-creation process caused by a space-time field absorb the provided energy differently depending on the temporal details of the external field.We employ two machine learning techniques,i.e.,neural networks and genetic-programming-based symbolic regression,to examine the dynamics of the electron-positron pair creation process with full space–time resolution inside the interaction zone of a supercritical electric field pulse.Both algorithms receive multiple sequences of partially dressed electronic and positronic spatial probability densities as training data and exploit their features as a function of the dressing strength in order to predict each particle’s spatial distribution inside the electric field.A linear combination of both predicted densities is then compared with the unambiguous total charge density,which also contains contributions associated with the independent vacuum polarization process.After its subtraction,the good match confirms the validity of the machine learning approach and lends some credibility to the validity of the predicted single-particle densities.