In the laboratory of Israeli physicists, attosecond extreme-ultraviolet pulses carrying quantum correlations between modes have been created. These correlations in amplitude and phase make individual pulses behave chaotically, while their joint reconstruction is almost perfectly stable. The result, obtained from an arXiv preprint dated 29 September 2026, opens the door to quantum attosecond science.
A team led by researchers from the Weizmann Institute in Rehovot used a two-mode bright squeezed vacuum to perturb high-harmonic generation in a gas medium. The signal and idler fields transferred their quantum fluctuations onto two families of harmonics, translating correlations from the infrared range into broadband XUV modes. The even harmonics served as a built-in attosecond interferometer: they recorded phase correlations with sub-cycle precision through the interference of indistinguishable paths.
Frame-by-frame covariance measurements revealed amplitude correlations, while analysis of the even harmonics revealed phase correlations. Temporal reconstruction showed how, over 30 attoseconds, the system transitions from maximum fluctuations to almost complete silence. Individual pulse trains, driven by the signal or idler field, exhibited excess noise, but joint reconstruction suppressed it thanks to the shared correlations.
Imagine two violins playing the same melody in different rooms: each sounds with a tremor, but together they create a pure chord without the slightest false note. That is exactly how quantum correlations turn the chaos of individual modes into a stable joint signal on attosecond scales.
This is not merely a technical trick. The approach makes it possible to directly observe and control the correlated dynamics of electrons in matter on their natural timescale. Correlation-resolved XUV imaging could provide new contrast mechanisms for spectroscopy and microscopy, and in the future, for quantum information on ultrafast timescales.
According to the preprint, the results lay the foundation for quantum attosecond science and show how the quantum properties of light are transferred to electronic processes in strong fields.
