arXiv:2209.13626 · Physical Review A

Ionic coherence in resonant above-threshold attosecond ionization spectroscopy

Saad Mehmood, Eva Lindroth, Luca Argenti

Published Mar 6, 2023• 5 citations

Abstract

The ionization of atoms with sequences of attosecond pulses gives rise to excited ionic states that are entangled with the emitted photoelectron. Still, the ionic ensemble preserves some coherence that can be controlled through the laser parameters. In helium, control of the $2s/2p\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}$ coherence is mediated by the autoionizing states below the $N=2$ threshold [Phys. Rev. Res. 3, 023233 (2021)]. In the present work we study the role of the resonances both below and above the $N=3$ threshold on the coherence of the $N=3\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}$ ion, in the attosecond pump-probe ionization of the helium atom, which we simulate using the newstock ab initio code. Due to the fine-structure splitting of the $N=3{\mathrm{He}}^{+}$ level, the ionic dipole beats on a picosecond timescale. We show how, from the dipole beating, it is possible to reconstruct the polarization of the ion at its inception.

DOI: 10.1103/physreva.107.033103

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arXiv:2209.13626 · Physical Review A

Ionic coherence in resonant above-threshold attosecond ionization spectroscopy

Saad Mehmood, Eva Lindroth, Luca Argenti

Published Mar 6, 2023• 5 citations

arXiv HTML PDF

Abstract

2s/2p\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}

coherence is mediated by the autoionizing states below the

N=2

threshold [Phys. Rev. Res. 3, 023233 (2021)]. In the present work we study the role of the resonances both below and above the

N=3

threshold on the coherence of the

N=3\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}

ion, in the attosecond pump-probe ionization of the helium atom, which we simulate using the newstock ab initio code. Due to the fine-structure splitting of the

N=3{\mathrm{He}}^{+}

level, the ionic dipole beats on a picosecond timescale. We show how, from the dipole beating, it is possible to reconstruct the polarization of the ion at its inception.

DOI: 10.1103/physreva.107.033103

Related papers

Coherence control in helium-ion ensembles

Saad Mehmood, Eva Lindroth, Luca Argenti

arXiv:2012.11040Physical Review ResearchJun 22, 20213 citations

Laser-assisted-autoionization dynamics of helium resonances with single attosecond pulses

Wei-Chun Chu, Song-Feng Zhao, C. D. Lin

The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.

arXiv:1205.4775Physical Review ASep 29, 201140 citations

Ionization and transient absorption control with a resonant attosecond clock

Luca Argenti

Metastable states are important actors in the ionisation of atoms and molecules. Sub-femtosecond extreme ultraviolet pulses can coherently populate several transiently bound states at once, thus starting the attosecond clocks which are required to monitor and control ultrafast electronic evolution above the ionisation threshold. Here we illustrate, from a theoretical point of view, the effects coherent superpositions of 1 P o doubly excited states in the helium atom have on channel-resolved photoelectron spectra as well as on the transient absorption spectrum of the atom in the extreme ultraviolet region, when they are created by a single-attosecond pulse in the presence of a strong few-cycle near-infrared/visible pulse which acts as a probe. Interference fringes varying rapidly with the pump-probe time delay are visible in both photoelectron and transient absorption spectra. From such fringes, the wave packet itself can conceivably be reconstructed. Conversely, all observables are modulated by the characteristic beating periods of the wave packet, so that control of partial ionisation yields, branching ratios, and light absorption or amplification can be achieved.Metastable states are important actors in the ionisation of atoms and molecules. Sub-femtosecond extreme ultraviolet pulses can coherently populate several transiently bound states at once, thus starting the attosecond clocks which are required to monitor and control ultrafast electronic evolution above the ionisation threshold. Here we illustrate, from a theoretical point of view, the effects coherent superpositions of 1 P o doubly excited states in the helium atom have on channel-resolved photoelectron spectra as well as on the transient absorption spectrum of the atom in the extreme ultraviolet region, when they are created by a single-attosecond pulse in the presence of a strong few-cycle near-infrared/visible pulse which acts as a probe. Interference fringes varying rapidly with the pump-probe time delay are visible in both photoelectron and transient absorption spectra. From such fringes, the wave packet itself can conceivably be reconstructed. Conversely, all observables are modulated by the characteristic beating periods of the wave packet, so that control of partial ionisation yields, branching ratios, and light absorption or amplification can be achieved.

Journal of Physics Conference SeriesApr 10, 20142 citations

The Dipole Response of an Ionization Threshold within Ultrashort and Strong Fields

Paul Birk

In this work, the strong-field-modified dipole response at the ionization threshold of helium is studied. The dipole response is induced by an attosecond pulse in the extreme ultraviolet spectral range and is manipulated by an ultrashort and strong femtosecond pulse in the near-infrared. To probe the response, the transient absorption spectrum of helium is recorded for different time delays between both pulses and different intensities of the femtosecond pulse. From the spectra, the dipole response of the ionization threshold is reconstructed, which is linked to the dynamics of excited electrons with energies in the transition region from bound to free. To identify the underlying processes of light-matter interaction leading to the observed structures in the time and spectral domain, different quantum-mechanical model simulations are conducted. As a result, the measured dipole response reveals light-induced energy shifts of the photoelectron’s kinetic energy close to the parent ion, signatures for field-driven recollisions of a photoelectron into the parent ion, and a temporal amplitude and phase gating mechanism. With the latter, the build-up dynamics of complex spectral structures are temporally resolved, which are the time-dependent separation and line-shape modification of the doubly excited Rydberg series as well as the temporal build-up of the ionization threshold.In this work, the strong-field-modified dipole response at the ionization threshold of helium is studied. The dipole response is induced by an attosecond pulse in the extreme ultraviolet spectral range and is manipulated by an ultrashort and strong femtosecond pulse in the near-infrared. To probe the response, the transient absorption spectrum of helium is recorded for different time delays between both pulses and different intensities of the femtosecond pulse. From the spectra, the dipole response of the ionization threshold is reconstructed, which is linked to the dynamics of excited electrons with energies in the transition region from bound to free. To identify the underlying processes of light-matter interaction leading to the observed structures in the time and spectral domain, different quantum-mechanical model simulations are conducted. As a result, the measured dipole response reveals light-induced energy shifts of the photoelectron’s kinetic energy close to the parent ion, signatures for field-driven recollisions of a photoelectron into the parent ion, and a temporal amplitude and phase gating mechanism. With the latter, the build-up dynamics of complex spectral structures are temporally resolved, which are the time-dependent separation and line-shape modification of the doubly excited Rydberg series as well as the temporal build-up of the ionization threshold.

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Yi-Jia Mao, Zhaohan Zhang, Yang Li +3 more

Quantitative control and measurement of quantum entanglement are essential for advancing quantum technologies. Photoionization induced by ultrashort laser pulses provides a unique platform for studying entanglement between photoelectrons and residual ions, representing one of the most intriguing quantum phenomena in attosecond physics. Although extensive studies have focused on the coherence properties within either the emitted electrons or the ions individually, the electron-ion entanglement has remained largely unexplored. In this work, we bridge this gap by investigating the resonance-enhanced multiphoton ionization of argon atoms driven by two time-delayed ultrashort ultraviolet pulses. Employing state-of-the-art first-principles multi-electron simulations, we demonstrate the ability to reconstruct and precisely manipulate the purity of electron quantum states through detailed analysis of the photoelectron angular distributions. Our results reveal distinct scattering-phase differences among various electron configurations within the same partial wave channel, providing unequivocal evidence of electron-ion correlation and entanglement. With the fast development of free-electron lasers, this study establishes an experimentally feasible framework for directly controlling quantum entanglement in ultrafast ionization processes, offering new insights and powerful methodologies for exploring complex electron dynamics in many-electron systems.Quantitative control and measurement of quantum entanglement are essential for advancing quantum technologies. Photoionization induced by ultrashort laser pulses provides a unique platform for studying entanglement between photoelectrons and residual ions, representing one of the most intriguing quantum phenomena in attosecond physics. Although extensive studies have focused on the coherence properties within either the emitted electrons or the ions individually, the electron-ion entanglement has remained largely unexplored. In this work, we bridge this gap by investigating the resonance-enhanced multiphoton ionization of argon atoms driven by two time-delayed ultrashort ultraviolet pulses. Employing state-of-the-art first-principles multi-electron simulations, we demonstrate the ability to reconstruct and precisely manipulate the purity of electron quantum states through detailed analysis of the photoelectron angular distributions. Our results reveal distinct scattering-phase differences among various electron configurations within the same partial wave channel, providing unequivocal evidence of electron-ion correlation and entanglement. With the fast development of free-electron lasers, this study establishes an experimentally feasible framework for directly controlling quantum entanglement in ultrafast ionization processes, offering new insights and powerful methodologies for exploring complex electron dynamics in many-electron systems.

Light Science & ApplicationsMar 6, 20261 citation

Probing electronic decoherence with high-resolution attosecond photoelectron interferometry

David Busto, Hugo Laurell, Daniel Finkelstein‐Shapiro +14 more

Abstract Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p $^2$ 2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic AbstractAbstract Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p $$^2$$ 2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract

arXiv:2111.12037The European Physical Journal DJul 1, 202226 citations

2s/2p\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}

coherence is mediated by the autoionizing states below the

N=2

threshold [Phys. Rev. Res. 3, 023233 (2021)]. In the present work we study the role of the resonances both below and above the

N=3

threshold on the coherence of the

N=3\phantom{\rule{4pt}{0ex}}{\mathrm{He}}^{+}

ion, in the attosecond pump-probe ionization of the helium atom, which we simulate using the newstock ab initio code. Due to the fine-structure splitting of the

N=3{\mathrm{He}}^{+}

level, the ionic dipole beats on a picosecond timescale. We show how, from the dipole beating, it is possible to reconstruct the polarization of the ion at its inception.

The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the

2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)

resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between

2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)

and

2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)

states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between

2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)

and

2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)

by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.

^2

2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract