Quantum Effects with an X-Ray Free-Electron Laser

A quantum kinetic equation coupled with Maxwell’s equation is used to estimate the laser power required at an x-ray free-electron laser (XFEL) facility to expose intrinsically quantum effects in the process of QED vacuum decay via spontaneous pair production. A $9$-TW-peak XFEL laser with photon energy of $8.3\mathrm{k}\mathrm{e}\mathrm{V}$ could be sufficient to initiate particle accumulation and the consequent formation of a plasma of spontaneously produced pairs. The evolution of the particle number in the plasma will exhibit non-Markovian aspects of the strong-field pair production process, and the plasma’s internal currents will generate an electric field whose interference with that of the laser leads to plasma oscillations.