Physicists exceed theoretical X-ray energy cutoff using two electrons

Researchers at TU Wien and UC San Diego fired intense ultraviolet lasers at helium atoms and produced X-ray photons with energies well above the standard cutoff predicted by theory. The effect relies on quantum correlations that let two electrons return to the atom simultaneously and release their energy together. The findings were published in Nature Photonics.

• The experiment revealed a second emission plateau beyond the conventional energy cutoff
• The effect appeared only with helium, not with argon or neon
• Both helium electrons returned to the atom at the same time and released energy at once
• The method could serve as a sensitive sensor of electron-electron correlations on attosecond scales