Quantum Tomography of Nonperturbative Harmonic Light from Solids

The interaction of intense light with matter gives rise to fascinating phenomena at the intersection of quantum optics and extreme nonlinear optics. High-harmonic generation (HHG) has attracted significant interest as a non-perturbative light-matter interaction process. Simultaneously, quantum optics explores the subtle interactions between light and matter at the level of individual quanta of light. Merging these two fields has led to the emergence of extreme nonlinear quantum optics, which challenges conventional assumptions about the quantum nature of light generated by nonlinear processes [1]–[3]. A recent experiment observed HHG from a solid driven by bright squeezed vacuum [2], but the created quantum state was not yet characterized. A central critical gap in the field remains measuring the quantum state of light generated by non-perturbative nonlinear processes, which requires a comprehensive sub-cycle quantum light tomography approach. It was so far unknown whether fragile quantum features like squeezing can survive in conditions of massive photon numbers and extreme nonlinearities.