Entanglement shapes attosecond photoionisation dynamics in CO₂
Freiburg, 23/10/2025
The Attosecond and Strong Field Physics group shows that ion polarisation and electron–ion entanglement shift photoelectron emission timing—key for reliable interpretation of ultrafast molecular experiments.
In a study combining experiments and theory, the Attosecond and Strong Field Physics group at the University of Freiburg, led by Prof. Dr. Giuseppe Sansone, demonstrated how entanglement affects the dynamics of photoionisation on the attosecond timescale. Using a complex detection apparatus capable of measuring the velocities of photoelectrons and photoions originating from the same molecule, the group’s researchers investigated the dynamics of the photoionisation process in a CO₂ molecule. They showed that the dynamics of photoelectron emission can be affected on an attosecond timescale by allowing the system to interact with an additional infrared laser pulse. This effect depends strongly on the entanglement between the photoelectron and photoion created in the photoionisation process.
“Our results indicate a clear effect of entanglement on the attosecond timescale during the photoionisation process of the photoelectron-photoion system. By applying more complex laser fields to the system, we might be able to manipulate its entanglement properties on an unprecedented timescale,” says Dr Ioannis Makos, the first author of the publication. “Our work will stimulate further studies into the deep connection between the entangled nature of the photoelectron-photoion system and its ultrafast dynamics. This connection has largely been overlooked in attosecond science until now” comments Sansone. The paper was published in Nature Communications.
“Our work will stimulate further studies into the deep connection between the entangled nature of the photoelectron-photoion system and its ultrafast dynamics. This connection has largely been overlooked in attosecond science until now.”
Prof. Dr. Giuseppe Sansone
Head of the Attosecond and Strong Field Physics at the University of Freiburg
Entanglement: foundation of quantum technologies
Photoionisation is one of the key experiments that has helped us to understand the quantised nature of light-matter interactions at a microscopic level. During this process, a quantum of energy is absorbed by a system, resulting in the release of a photoelectron. In molecules, this process results in the formation of a photoelectron that swiftly leaves the photoion. Due to the presence of several energy levels from which the electron can be emitted, the photoionisation process establishes a link between the properties of the departing photoelectron and those of the remaining photoion, which is usually referred to as entanglement of the composite photoelectron–photoion system. The characterisation and control of entanglement is one of the most peculiar effects introduced by the quantum mechanical description of the world, and lies at the heart of several quantum technologies. Photoionisation can easily be triggered by attosecond (1 as =10-18s) pulses in the extreme ultraviolet range. These are the shortest events created to date, and their importance was recognised with award of the Nobel Prize in Physics in 2023 to Anne L’Huillier, Pierre Agostini and Ferencz Krausz for their pioneering work in the development of this research field.
Marie Skłodowska-Curie Doctoral Training Network Qu-ATTO
The study was carried out within the framework of the Marie Skłodowska-Curie Doctoral Training Network QU-ATTO (Quantum Information Science and Ultrafast Nonlinear Coherent Control at the Attosecond Timescale), coordinated by Sansone. The network brings together several of the world’s leading research groups in the fields of attosecond and quantum information science.
Further information
- Original title of the study: Entanglement in photoionisation reveals the effect of ionic coupling in attosecond time delays. I. Makos, D. Busto, J. Benda, D. Ertel, B. Merzuk, B. Steiner, F. Frassetto, L. Poletto, C. D. Schröter, T. Pfeifer, R. Moshammer, S. Patchkovskii, Z. Mašín, and G. Sansone, Nature Communications 16, 8554
- DOI: doi.org/10.1038/s41467-025-64182-8