Parametric model for high-order harmonic generation with quantized fields

There is a growing interest in the quantum features of the high-harmonic modes in the attosecond physics community, both experimentally and theoretically (see e.g. [1-4]). In this contribution, we present a quantum optical model for high-order harmonic generation, in which both the driving laser field and the high-harmonic modes are quantized, while the target material appears via parameters only [5]. This model is independent from the excited material system (e.g. atom, molecule, solid) to a large extent. We give approximate analytic and numerically exact solutions of the time evolution of the field modes. By investigating the time-dependent photon number distribution for the driving laser mode (starting in a coherent state) and the harmonic modes, we show that although both of these field modes are approximately in a coherent state at the initial stage of the evolution, this then develops rapidly into a non-classical quantum state. Our results suggest that high-harmonic radiation has non-trivial quantum features, which may also affect some of the processes induced in the typical target systems of HHG beamlines.



[1] N. Tsatrafyllis et al., Phys. Rev. Lett. 122, 193602 (2019).

[2] A. Gorlach et al., Nat. Comm. 11, 4598 (2020)

[3] Á Gombkötő et al., Phys. Rev. A 101 (1), 013418 (2020)

[4] P. Stammer et al., PRX Quantum 4, 010201 (2023).

[5] Á. Gombkötő et al., arXiv:2311.01726 [quant-ph]