High Harmonic Generation by Bright Squeezed Vacuum

We observe non-perturbative high harmonic generation in solids pumped by a macroscopic quantum state of light, bright squeezed vacuum (BSV), which we generate in a single spatiotemporal mode. Due to its broad photon-number distribution, covering states from 0 to 2 × 10^13 photons per pulse, and sub-cycle electric field fluctuations over ±1V/Å, BSV provides access to free carrier dynamics within a much broader range of peak intensities than accessible with coherent light. It is also considerably more efficient in the generation of high harmonics than coherent light of the same mean intensity.