Quantum Features of High-Order Harmonics
Without doubts – High-Order Harmonics are non-classical! The QUANTUM group at LOA contributes to pioneering a new research field by unifying two historically distant domains: quantum optics (Nobel 2022) and high-harmonic generation (HHG) and attosecond science (Nobel 2023). Following their initial demonstration [1], the QUANTUM group have further substantiated that the intense-laser-driven process of HHG in a semiconductor is a source of light with profound quantum properties.
Their recently published experiments unambiguously confirm the non-classical character of the HHG light through the violation of a Cauchy-Schwarz inequality (Rij greater than 1 means non-classical). They demonstrate that the different colors—or harmonics (indices i and j)—are linked by strong quantum correlations. Crucially, their analysis reveals that the harmonics are likely emitted as a “displaced squeezed state,” a complex and useful quantum resource. Indeed, this quantum state of light possesses a low-dimensional structure, an essential property for quantum computation and sensing. These results establish solid-state HHG as a scalable, room-temperature resource, opening a new route towards applications in quantum technologies and basic science.
Find the open-access publication here: