Resolving Quantum Interference Black-Box through Attosecond Photoionization Spectroscopy

Abstract Multiphoton light-matter interactions invoke a so-called ‘Black Box’ in which the experimental observations contain the quantum interference between multiple pathways (1–3). Here, we employ attosecond coincidence metrology (4, 5) with a partial wave polarization manipulator to deduce the pathway interference within this quantum ‘Black Box’ (6) for two-photon ionization of neon and argon. The angle-dependent and attosecond time-resolved photoelectron spectra are measured across a broad energy range. Two-photon phase shifts for each partial wave are reconstructed through the comprehensive analysis of these photoelectron spectra. We resolve the quantum interference between the p → d → p and p → s → p ionization pathways, in agreement with our theoretical simulations. Our approach thus provides a microscope to look inside the ‘black box’ of pathway interference in ultrafast dynamics of atoms, molecules, and condensed matter.