Experimental evidences of quantum properties in a high-harmonic based bipartite system

High-harmonic generation (HHG) is a highly non-linear frequency up conversion process, mostly studied from a classical point of view. Recently, independent theoretical investigations about the quantum nature of HHG predicted several, non-classical effects in the high-harmonic radiation [1, 2, 3]. In addition to the fundamental interest in understanding the physics behind HHG, a better understanding of the quantum nature of this process could potentially have a broad impact on the rapidly developing field of quantum technologies. It is in this context that present here our experimental photon statistics investigations showing the quantum nature of the HHG process.