Attosecond science is maturing into a transformative tool for measuring and understanding electronic dynamics on their fundamental time scales, but its extension to complex systems is hampered by several challenges. To date, spectroscopy with attosecond pulses has been missing the ability to distinguish chiral molecules, because of a lack of circularly polarized attosecond pulses. We have developed attosecond metrology in circular polarization1 and applied it to the study of continuum–continuum transitions in electron vortices, establishing a general framework for attosecond circular-dichroism chronoscopy2. Application to photoionizations of s orbitals enables the first experimental separation of photoionization and measurement-induced delays3. The first application of circularly polarized attosecond pulses to chiral-sensitive experiments enabled us to observe and control photoelectron circular dichroism (PECD) on the attosecond timescale and to directly measure chiral photoionization delays of up to ~240 attoseconds4, which contain a ~60 as contribution from the chirality of continuum-continuum transitions.
In parallel, soft-X-ray absorption spectroscopy with attosecond pulses has been developed, first in gases5,6 and then in liquids7, enabling element-specific studies of solvated molecules in liquid water. This novel technique has been used to reveal the electronic and structural dynamics underlying ultrafast proton transfer in solvated urea8 and the dephasing of conical-intersection-driven electronic dynamics in solvated pyrazine9.
These advances chart a promising path for attosecond-resolved studies of molecular function in aqueous environments, opening exciting opportunities for understanding radiation damage, solvation dynamics, and chiral interactions at their fundamental electronic timescale10.

References:

1 Han, M. et al., Optica 10, 1044–1052 (2023)
2 Han, M. et al., Nature Phys. 19, 230–236 (2023)
3 Han, M. et al., Science Advances 10, eadj2629 (2024)
4 Han, M. et al., Nature 645, 95-100 (2025)
5 Pertot, Y. et al., Science 355, 264-267 (2017)
6 Zinchenko, K. et al., Science 371, 489 (2021)
7 Smith, A. et al., J. Phys. Chem. Lett. 11, 1981-1988 (2020)
8 Yin, Z. et al., Nature 619, 749–754 (2023)
9 Chang, Z. et al., Nature Phys. 21, 137–145 (2024)
10 Wörner H. J. and Wolf J.P., Nat. Rev. Chem. 9, 185 (2025)