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Time-domain interference in photo-double-ionization revealing nonseparable two-electron wavefunctions

Y. Hikosaka1,*, T. Kaneyasu2,3, S. Wada4, H. Ota5,2, M. Katoh6,2, and F. Koike7

  • *Contact author: hikosaka@las.u-toyama.ac.jp
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Phys. Rev. Research 8, 033332 – Published 17 September, 2026

DOI: https://doi.org/10.1103/x7zf-dx8m

Abstract

We reveal interference patterns in photo-double-ionization spectra, produced by the interaction of argon atoms with an extreme-ultraviolet light wave packet in the form of a double pulse with variable pulse separation. These interference features provide direct evidence for nonseparable two-electron wavefunctions, an insight previously deemed beyond the reach of electron spectroscopy. This advance leverages the recently uncovered longitudinal coherence of undulator radiation, opening new avenues for attosecond-scale quantum interference experiments. The present undulator-based methodology is straightforwardly extendable into the x-ray regime, potentially offering a platform for investigating multielectron correlations associated with core-hole creation and decay.

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Phys. Rev. Research 8, 033332– Published 17 September, 2026
  • Received 21 August 2025
  • Revised 31 December 2025
  • Accepted 18 August 2026
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