High-order harmonic generation in an atomic gas target (GHHG) by a near-infrared laser pulse is still the most widespread and effective way to create attosecond pulses of light [1]. In this talk, we present and discuss recent results in a few topics having deep quantum features.
Phase space analysis and accurate tracking of the instantaneous energy distribution reveals that quantum interference between tunneling and over-the-barrier pathways of escape plays an important role during the liberation of an atomic electron by a linearly polarized single-cycle near-infrared laser pulse, despite that the peak laser intensity seems to correspond to tunnel ionization [2]. This leads us to a new method to define the non-zero tunnel exit momentum of the electron, based on the quantum momentum function, and in a good agreement with recent experimental results.
Based on our recent result with 1D model potentials for strong-field physics [3], we discuss how to define a 1D model potential in such a way that the essential high-frequency components of the dipole acceleration from the corresponding 1D quantum simulation are sufficiently close to those of the true 3D case, without any scaling of other physical parameters.
The role and possible use of quantum entanglement between particles participating in strong-field processes is an emerging research topic with high scientific potential. We investigated the time evolution of quantum entanglement between an electron, liberated by a strong few-cycle laser pulse, and its parent ion core. Since the standard procedure seems numerically prohibitive in 3D, we introduced a method to quantify the quantum correlation based on the reduced density matrices of the directional subspaces to compute an approximate entanglement entropy [4].
There is a growing interest in the quantum features of the high-harmonic modes in the attosecond physics community. I will present a quantum optical model for the high-order harmonic generation, in which both the driving NIR field and the high harmonic modes are quantized, while the involved material system (e.g. noble gas) appears via parameters only [5]. Our results indicate 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] https://eli-laser.eu/ [2] Hack et al., Phys. Rev. A 104, L031102; Czirják et al., Opt. Commun. 179, 29 (2000) [3] Majorosi et al., Phys. Rev. A 98, 023401 (2018); Phys. Rev. A 101, 023405 (2020) [4] Majorosi et al., Phys. Rev. A 96, 043412 (2017) [5] Gombkötő et al., Phys. Rev. A 94, 013853 (2016); arXiv:2311.01726 [quant-ph]