Formation of a Schrödinger cat state of a strong circularly polarized laser field due to Thomson scattering by free electrons
Phys. Rev. A 112, 013117 – Published 21 July, 2025
DOI: https://doi.org/10.1103/3gjp-f7br
Abstract
Ionization of a target gas by a strong laser field, which is the first step for many processes studied in strong-field physics, results in the appearance of free electrons. Recently, we showed that the interaction of the laser field with these electrons affects the quantum state of the field, leading to the formation of nonclassical and non-Gaussian field states [Phys. Rev. A 110, 023115 (2024)]. In this paper we generalize our model to the multimode case, which allows us to consider Thomson scattering (TS) of the laser field by the electrons. We show that for sufficiently long pulses under typical experimental conditions TS causes coherent transfer of photons from the strong laser mode to weak modes with close frequencies and wave vectors. This results in a displacement of the initial coherent state of the laser field similar to that recently discovered and caused by the high-order harmonic generation (HHG) process [M. Lewenstein et al., Nat. Phys. 17, 1104 (2021)]. The similarity with HHG suggests that, by conditioning on TS, multiphoton Schrödinger cat states of the laser field can be generated. The TS mechanism has a different dependence on the pulse parameters compared with the HHG mechanism, which may facilitate more efficient and robust generation of cat states. In particular, it also works for circularly polarized fields, in which case HHG does not occur.
