In 2010, an experiment led by Ferenc Krausz at the Max Planck Institute of Quantum Optics, highlighted a discrepancy between theory and experimental results concerning photoemission delays in neon atoms. L'Huillier group in Lund solved this problem in 2017 by experimentally uncovering the contribution of shake-up electrons. By correcting for this effect L'Huillier group found an excellent agreement with theory.