Quantum entanglement in attosecond ionisation
Lead Research Organisation:
Imperial College London
Department Name: Physics
Abstract
Two of the quantum phenomena at the very heart of the foundation of quantum mechanics, as it emerged about 100 years ago, were photoionisation (Einstein's 1921 Nobel prize for the discovery of the law of the photoelectric effect) and later on quantum entanglement, which led to the famous Einstein-Podolsky-Rosen (EPR) paradox and the puzzling concept of 'spooky action at a distance'.
The project proposed here joins these two fundamental concepts into a single research direction studying the formation and control of entanglement in photoionisation by ultra-short laser pulses. This theoretical endeavour emerges as very timely due to the recent developments in ultrafast laser technology that have opened the way to the experimental study of the very first few femtoseconds of the motion of electrons triggered by ionisation. A wide range of physical scenarios of photoionisation that previously could not be observed as they evolve in time, have become experimentally accessible to time-resolved spectroscopy performed with the new generation ultrafast light sources at both university laboratories and the major international laser facilities around the world. These scenarios encompass various regimes of the light-matter interaction, from the single- and multi-photon perturbative one to the strong-field non-perturbative one, as well as
various statistical properties of the ionising light, from fully coherent to stochastic light pulses.
By using quantum information and quantum state tomography approaches, we aim to discover new physical phenomena underpinned by quantum entanglement in ionising many-electron systems, occurring on the attosecond (10^{-18} of a second) time scale. As part of this research, we will study quantum entanglement between the photoelectron and the remaining ion, devise Bell-test experiments with photoelectrons to probe this entanglement and find out about the effect of measurement on the quantum many-electron dynamics. The proposed research programme will apply the world-leading theoretical and computational tools we developed to study the nature of
charge migration and other previously unexplored attosecond-scale processes in atoms and molecules, including the building blocks of biomolecules. These tools, originally based on Feynman's diagrammatic approach to quantum mechanical perturbation theory, are significantly
extended by us to describe the large-amplitude motion of the ionised electron.
As a result of our work, there will emerge the presently lacking picture of the effect of quantum entanglement and quantum measurement in photo-ionised many-body systems. The knowledge gained from this research will lead to a new level of understanding of the first moments in the electronic excitation of matter. Ultimately, this may lead to new ways to control the radiation damage processes, with direct implications on radiobiology and eventually on radiotherapy. For instance, it has been shown that electronic excitation in key molecular building blocks of matter is followed by a universal primary event - sub-femtosecond to few femtosecond migration of electric charge across nanometres. This
charge migration is expected to be extremely important for triggering the subsequent nuclear dynamics and therefore ultimately controlling the chemical change in what has become known as "attochemistry".
The project proposed here joins these two fundamental concepts into a single research direction studying the formation and control of entanglement in photoionisation by ultra-short laser pulses. This theoretical endeavour emerges as very timely due to the recent developments in ultrafast laser technology that have opened the way to the experimental study of the very first few femtoseconds of the motion of electrons triggered by ionisation. A wide range of physical scenarios of photoionisation that previously could not be observed as they evolve in time, have become experimentally accessible to time-resolved spectroscopy performed with the new generation ultrafast light sources at both university laboratories and the major international laser facilities around the world. These scenarios encompass various regimes of the light-matter interaction, from the single- and multi-photon perturbative one to the strong-field non-perturbative one, as well as
various statistical properties of the ionising light, from fully coherent to stochastic light pulses.
By using quantum information and quantum state tomography approaches, we aim to discover new physical phenomena underpinned by quantum entanglement in ionising many-electron systems, occurring on the attosecond (10^{-18} of a second) time scale. As part of this research, we will study quantum entanglement between the photoelectron and the remaining ion, devise Bell-test experiments with photoelectrons to probe this entanglement and find out about the effect of measurement on the quantum many-electron dynamics. The proposed research programme will apply the world-leading theoretical and computational tools we developed to study the nature of
charge migration and other previously unexplored attosecond-scale processes in atoms and molecules, including the building blocks of biomolecules. These tools, originally based on Feynman's diagrammatic approach to quantum mechanical perturbation theory, are significantly
extended by us to describe the large-amplitude motion of the ionised electron.
As a result of our work, there will emerge the presently lacking picture of the effect of quantum entanglement and quantum measurement in photo-ionised many-body systems. The knowledge gained from this research will lead to a new level of understanding of the first moments in the electronic excitation of matter. Ultimately, this may lead to new ways to control the radiation damage processes, with direct implications on radiobiology and eventually on radiotherapy. For instance, it has been shown that electronic excitation in key molecular building blocks of matter is followed by a universal primary event - sub-femtosecond to few femtosecond migration of electric charge across nanometres. This
charge migration is expected to be extremely important for triggering the subsequent nuclear dynamics and therefore ultimately controlling the chemical change in what has become known as "attochemistry".
Publications
Guo Z
(2024)
Experimental demonstration of attosecond pump-probe spectroscopy with an X-ray free-electron laser
in Nature Photonics
Guo Zhaoheng
(2024)
Experimental Demonstration of Attosecond Pump-Probe Spectroscopy with an X-ray Free-Electron Laser
in arXiv e-prints
Ruberti M
(2023)
Advances in modeling attosecond electron dynamics in molecular photoionization
in WIREs Computational Molecular Science
Ruberti M
(2022)
Quantum coherence in molecular photoionization.
in Physical chemistry chemical physics : PCCP
Ruberti Marco
(2023)
Bell test of quantum entanglement in attosecond photoionization
in arXiv e-prints
Schwickert D
(2022)
Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy.
in Structural dynamics (Melville, N.Y.)
Schwickert D
(2022)
Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time.
in Science advances
| Description | We unveiled the nature of the quantum coherent many-body dynamics in molecules upon attosecond photoionization [M. Ruberti, S. Patchkovskii, V. Averbukh, "Quantum Coherence in Molecular Photoionization", Physical Chemistry Chemical Physics 24 (33), 19673-19686 (2022); O. G. Alexander, J. P. Marangos, M. Ruberti, M. Vacher, "Attosecond electron dynamics in molecular systems" in "Advances in Atomic, Molecular and Optical Physics", Volume 72, edited by Louis F. DiMauro, Helene Perrin and Susanne F. Yelin, Elsevier Academic Press, 183-252 (2023). ISBN: 978-0-323-99252-7]. We demonstrated and characterized ultrafast quantum-coherent many-electron dynamics in polyatomic molecules upon X-ray photoionization. In collaboration with experimental attosecond physics group of Dr T. Laarmann (DESY) we unraveled the ultrafast photoionization dynamics of molecular glycine by ultrafast X-ray pump-probe spectroscopy [D. Schwickert et al., "Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy", Structural Dynamics 9 (6), 064301 (2022) (Editor's Pick); D. Schwickert et al., "Electronic quantum coherence in glycine molecules probed with ultrashort x-ray pulses in real time", Science Advances 8 (22), eabn6848 (2022)]. We led the theoretical modelling and interpretation of the experiment performed at the FLASH X-ray free electron laser in Hamburg. This work provided the first direct observation (i.e. through electronic observables) of femtosecond coherent electron dynamics of molecular valence-ionized states. We collaborated on the experimental Attosecond Campaign "Real-time Observation of Ultrafast Electron Motion using Attosecond XFEL Pulses" led by the experimental attosecond group (Dr J. Cryan and Prof A. Marinelli) of the SLAC National Laboratory (USA) at the world-leading LCLS X-ray FEL facility (Stanford). In the framework of this campaign, we seek to establish the effect of coherence in the outer-shell ionization of molecular targets with the aim of directly measuring hole migration using soft X-ray pulses. In the first research output of this collaboration [Z. Guo et al., "Experimental Demonstration of Attosecond Pump-Probe Spectroscopy with an X-ray Free-Electron Laser", arXiv:2401.15250 [physics.acc-ph], Nat. Photon. (2024), accepted for publication], to which MR and VA contributed, the generation and control of sub-femtosecond pulse pairs from a two-colour X-ray free-electron laser (XFEL) was reported for the first time, demonstrating the ability to perform pump-probe experiments with sub-femtosecond resolution and atomic site specificity. MR has also led the theoretical modelling and interpretation of the first molecular pump-probe experiment exploiting the attosecond time duration of the X-ray FEL pulses at LCLS-II. This work, which unveils the charge migration dynamics and decay in the outer-valence energy region of the photoionized para-aminophenol molecule, is currently being prepared for submission [Attosecond Coherent "Electron Motion in a Photoionized Aromatic System", in preparation for submission to Science]. The theoretical description of these experiments are based on the theoretical and computational methodology that we had developed before this project to accurately model attosecond molecular photoionization dynamics and that they have recently reviewed [M. Ruberti, V. Averbukh, "Advances in modelling attosecond electron dynamics in molecular photoionization", WIREs: Computational Molecular Science 13, e1673 (2023)]. The advanced theoretical description of the photoionization dynamics by we identified the quantum entanglement between the photoelectron and its parent ion as one of the key factors limiting the quantum coherence that can be observed within each subsystem when interrogated individually by probe measurements. However, contrary to case of quantum coherence, no direct measurement of quantum entanglement in attosecond photoionization experiments had yet been achieved. We theoretically designed the first direct probe to detect quantum entanglement between the photoelectron and its parent ion in attosecond atomic photoionization, by means of a Bell test [M. Ruberti, V. Averbukh, F. Mintert, "Bell Test of Quantum Entanglement in Attosecond Photoionization", arXiv:2312.05036 [physics.atom-ph] (2023), manuscript under review for publication in Physical Review X]. The devised Bell Test detects entanglement between the bound states of the ion and the spin of the emitted electron. They simulated it numerically for noble-gas atoms photoionized by circularly polarized laser pulses. The results predict that strong violation of the Bell inequalities can be observed in attosecond photoionization experiments, demonstrating that entanglement is central to a deeper understanding of ultrafast photoionization phenomena. This key theoretical result provides a completely new perspective on the photoionization phenomenon and on attosecond physics, paving the way to the direct observation of quantum correlations in the context of ultrafast photoionization of many-electron systems, where they have thus far remained elusive. |
| Exploitation Route | The results can guide the conceptualisation of laboratory experiments. |
| Sectors | Education |
| Description | The fundamental goal of attosecond physics is to understand electron dynamics in matter on its natural, ultrafast timescale. The most basic response of matter upon interaction with ultrafast laser pulses features photoionization, a process where an electron separates from its parent ion. Entanglement, the iconic quantum effect that led to the Einstein-Podolsky-Rosen paradox and the puzzling concept of 'spooky action at a distance', is supposedly a critical component of photoionization dynamics, but it remained thus far elusive in attosecond physics. We filled this gap and provided key insights into the quantum entanglement in attosecond photoionization by devising a direct way to detect it by means of a Bell Test. The common description of ultrafast photoionization experiments placed its focus on the internal coherent dynamics of the photoelectron and parent ion born during the photoionization event. We provided a transformative approach and advanced the state-of-the-art of attophysics by devising a direct probe of entanglement in attosecond photoionization and paving the way to new spectroscopies based on quantum correlations. Our work shifts the paradigm of attophysics, from the search for manifestations of internal quantum coherence within the individual ion and photoelectron systems to the pursuit of quantum correlations between them, and pushes the attophysics field into the study of genuinely quantum-mechanical effects at the shortest accessible timescale. Our work was enabled by the extension of methods of quantum information theory (Bell inequality) to attophysics, thus establishing a fruitful connection between the two areas. |
| First Year Of Impact | 2023 |
| Sector | Digital/Communication/Information Technologies (including Software) |
| Description | Pulse Institute Stanford University |
| Organisation | Stanford University |
| Country | United States |
| Sector | Academic/University |
| PI Contribution | theoretical modelling for experiments at the XFEL facility |
| Collaborator Contribution | experimental data from the XFEL facility |
| Impact | no published outputs yet |
| Start Year | 2022 |
| Description | Invited talk |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | The 15th Femtochemistry Conference (FEMTO15) |
| Year(s) Of Engagement Activity | 2023 |
| Description | Invited talk |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | 2nd "Quantum Battles in Attoscience" conference |
| Year(s) Of Engagement Activity | 2023 |