Quantized Attosecond Science: Merging High Harmonic Generation with Quantum Optics and Information

High Harmonic Generation (HHG) is the cornerstone of attosecond science, yet it is traditionally modeled as a closed quantum system driven by a classical laser field. This paradigm overlooks the rich open-system dynamics that emerge when the electron, the pump field, and the harmonic emission become strongly correlated across many unobserved degrees of freedom. By treating the electron—with its myriad coupling channels—and the light fields as dynamical quantum participants, we can reframe HHG through the lens of quantum optics and quantum information science (QIS).

I will first review the historical transition of HHG from a semi-classical phenomenon toward a fully quantized framework, highlighting key theoretical and experimental milestones. I will then present our work on driving HHG with quantum light, exploring how non-classical states such as bright squeezed vacuum allow us to resolve quantum fluctuations on attosecond timescales through in-situ quantum tomography of the interaction. Finally, I will introduce Attosecond Path Qubits and show how HHG provides a unique platform for exploring decoherence at the atomic and attosecond scales.