Physicists control quantum entanglement at attosecond timescales
An international team of physicists has demonstrated for the first time how quantum entanglement between an electron and a molecular ion can be controlled at the attosecond scale, one billionth of a billionth of a second, opening new pathways for manipulating quantum coherence in molecules. The findings, published in Nature on March 31, mark a significant advance in attosecond science.
Researchers from the Max Born Institute in Berlin, the Universidad Autónoma de Madrid, and IMDEA Nanociencia ionized hydrogen molecules using pairs of attosecond laser pulses in the extreme ultraviolet range combined with a longer infrared pulse. When a photon strips an electron from a hydrogen molecule, the resulting ion and the escaping photoelectron become quantum entangled, their properties linked in a way that has no classical equivalent.
That entanglement presents a fundamental challenge: it limits the ability to observe coherent electronic dynamics within the ion or the photoelectron individually. The team, led by Marc Vrakking of the Max Born Institute, showed that by varying the time delay between the two attosecond pulses, they could tune the degree of entanglement between the ion and the photoelectron, directly controlling the coherence of electronic dynamics in the residual hydrogen ion.
The advance builds on nearly a decade of theoretical and experimental groundwork. A 2021 paper in Physical Review Letters by Vrakking proposed the two-pulse scheme for controlling ion-photoelectron entanglement and predicted that quantum beat signals in the ion would reflect the degree of entanglement. A 2022 experiment by the same team at the Max Born Institute provided the first experimental demonstration of entanglement control in an attosecond pump-probe setup, though that work focused on vibrational wave packets. The new Nature study extends those results to electronic coherence, a more complex and practically relevant regime.
The ability to modulate quantum entanglement in a molecular system carries implications beyond fundamental physics. According to IMDEA Nanociencia, the work opens pathways for manipulating quantum coherence and entanglement in complex molecular systems, with potential relevance for quantum information technologies. The results also provide a new diagnostic tool: measuring the coherence of ionic dynamics can now serve as a direct probe of the entanglement degree in the ion-photoelectron system, a capability that may prove essential as attosecond science turns toward larger and biologically relevant molecules.
