Attophysics is at the forefront of time-resolved spectroscopy. Indeed, it harnesses the shortest light pulse probe that can be produced experimentally, thanks to the high harmonic generation (HHG) process. A standard way to trigger HHG is to submit an atomic system to an oscillating electromagnetic field whose strength compares with the Coulomb potential bounding electrons with their nuclei. This non-linear, non-perturbative optical effect produces a broadband coherent radiation in the extreme ultraviolet (XUV) frequency range, which forms attosecond pulses (1e-18 s). Since its discovery in the late 1980s, continuous experimental and theoretical efforts have been dedicated to get a complete understanding of this complex phenomenon. Despite the tremendous success of attosecond science, there is still no consensus about a quantum description of the process. We foresee that such a description of HHG would push forward our understanding of non-linear optics and open up new perspectives for attosecond science.