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Physical Review A

Remote control of the dissociative ionization of H 2 based on electron- H 2 + entanglement

Junping Wang, Feng He

Published Apr 11, 2018• 8 citations
Publisher

Abstract

The single ionization of ${\mathrm{H}}_{2}$ in strong laser fields creates the correlated electron-${{\mathrm{H}}_{2}}^{+}$ pair. Based on such a correlation, we conceive a strategy to control the energy spectra of the freed electron or dissociative fragments by simulating the time-dependent Schr\"odinger equation. Two attosecond pulses in a train produce the replica of electron-${{\mathrm{H}}_{2}}^{+}$ pairs, which are to be steered by a time-delayed phase-stabilized (mid)infrared laser pulse. By controlling the behavior of the freed electron, the dissociation of ${{\mathrm{H}}_{2}}^{+}$ can be controlled even though there is no direct laser-${{\mathrm{H}}_{2}}^{+}$ coupling. On the other hand, the photoelectron energy spectra can be manipulated via laser-${{\mathrm{H}}_{2}}^{+}$ coupling. This study demonstrates the entanglement of molecular quantum wave packets, and affords a route to remotely control molecular dissociative ionization.

DOI
10.1103/physreva.97.043411

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The single ionization of H2{\mathrm{H}}_{2}H2​ in strong laser fields creates the correlated electron-H2+{{\mathrm{H}}_{2}}^{+}H2​+ pair. Based on such a correlation, we conceive a strategy to control the energy spectra of the freed electron or dissociative fragments by simulating the time-dependent Schr"odinger equation. Two attosecond pulses in a train produce the replica of electron-H2+{{\mathrm{H}}_{2}}^{+}H2​+ pairs, which are to be steered by a time-delayed phase-stabilized (mid)infrared laser pulse. By controlling the behavior of the freed electron, the dissociation of H2+{{\mathrm{H}}_{2}}^{+}H2​+ can be controlled even though there is no direct laser-H2+{{\mathrm{H}}_{2}}^{+}H2​+ coupling. On the other hand, the photoelectron energy spectra can be manipulated via laser-H2+{{\mathrm{H}}_{2}}^{+}H2​+ coupling. This study demonstrates the entanglement of molecular quantum wave packets, and affords a route to remotely control molecular dissociative ionization.
Orthogonally polarized two-color sequential laser pulses are used to control the electron localization in the dissociation of H2+{}_{2}{}^{+}2​+. The first single attosecond pulse, whose polarization axis is perpendicular to the molecular axis, excites H2+{}_{2}{}^{+}2​+ from $1s{\ensuremath{\sigma}}_{g}$ to $2p{\ensuremath{\pi}}_{u}$, and the time-delayed infrared pulse, whose polarization axis is parallel to the molecular axis, steers the electron between two nuclei. The simulation of the time-dependent Schr\"odinger equation predicts the control degree of the electron localization can be up to 90% with the current laser technology. In this article, we reveal that the mechanism for this asymmetric localization is due to the mixture of $2p{\ensuremath{\pi}}_{g}$ and $2p{\ensuremath{\pi}}_{u}$, instead of $1s{\ensuremath{\sigma}}_{g}$and $2p{\ensuremath{\sigma}}_{u}$ in the previous studies.
Laser Induced Dissociation Control of H2+H_2^+H2+​ and H32+H_3^{2+}H32+​
Laser induced dissociation control of the symmetric diatomic molecular ion H2+H_2^+H2+​ and the triatomic molecular ion H32+H_3^{2+}H32+​ is discussed. The simulation results demonstrate that a long-wavelength terahertz or mid-infrared laser pulse can be used to control the electrons of the dissociative states after the excitation of an ultrashort ultraviolet (UV) laser pulse. For H2+,H_2^+,H2+​, there exists an effective time, which increases with increasing pulse duration of the UV laser pulse, for controlling the molecular dissociation. For the electrons of the 1sσg1sσ_g1sσg​ state, they move along the polarization direction of the dissociation control electric field. In contrast, for the electrons of the 2pσu2pσ_u2pσu​ state, they move in the opposite direction to that of the electric force. And for the triatomic molecule H32+H_3^{2+}H32+​, the electron dissociation control can also be realized by changing the central wavelength of the exciting UV pulse.
We examine the attosecond electron recollision dissociation of D2+\mathrm{D}_{2}{}^{+}D2​+ recently demonstrated experimentally [H. Niikura et al., Nature (London) 421, 826 (2003)] from a coherent control perspective. In this process, a strong laser field incident on D2{\mathrm{D}}_{2}D2​ ionizes an electron, accelerates the electron in the laser field to eV energies, and then drives the electron to recollide with the parent ion, causing D2+\mathrm{D}_{2}{}^{+}D2​+ dissociation. A number of results are demonstrated. First, a full dimensional strong field approximation model is constructed and shown to be in agreement with the original experiment. This is then used to rigorously demonstrate that the experiment is an example of coherent pump-dump control. Second, extensions to bichromatic coherent control are proposed by considering dissociative recollision of molecules prepared in a coherent superposition of vibrational states. Third, by comparing the results to similar scenarios involving field-free attosecond scattering of independently prepared D2+\mathrm{D}_{2}{}^{+}D2​+ and electron wave packets, recollision dissociation is shown to provide an example of wave-packet coherent control of reactive scattering. Fourth, this analysis makes clear that it is the temporal correlations between the continuum electron and D2+\mathrm{D}_{2}{}^{+}D2​+ wave packet, and not entanglement, that are crucial for the subfemtosecond probing resolution demonstrated in the experiment. This result clarifies some misconceptions regarding the importance of entanglement in the recollision probing of D2+\mathrm{D}_{2}{}^{+}D2​+. Finally, signatures of entanglement between the recollision electron and the atomic fragments, detectable via coincidence measurements, are identified.
Quantum Dynamics of H2+H_2^+H2+​ in Orthogonal Two-Color Fields
We present full-dimensional quantum simulations of H2+H_2^+H2+​ dissociative ionization driven by strong orthogonal laser fields. We consider equal-frequency orthogonal components, which generate elliptical or circular polarization depending on their relative phase and amplitude, as well as orthogonal 800800800- and 400400400-nm two-color fields. These two-dimensional fields strongly modify the fragmentation dynamics. Most notably, we identify a high-energy peak in the proton kinetic-energy-release (KER) spectrum at approximately 4−54-54−5 eV that is absent from the corresponding single-color, linearly polarized calculations. The yield of this peak can be coherently controlled by varying the relative carrier-envelope phase of the perpendicular field component. The perpendicular field also disrupts the clear electron-proton energy-sharing pattern observed in the main 3−3.53-3.53−3.5 eV dissociation channel, indicating more complex multichannel dynamics. Time-dependent state projections and calculations initiated from individual excited states attribute the additional peak to laser-induced vibrational excitation of H2+H_2^+H2+​. Furthermore, the perpendicular field rotates the fragment angular distributions, causing the most probable proton and electron emission directions to deviate substantially from the principal zzz axis. These findings demonstrate that the spatial and temporal geometry of orthogonal laser fields provides an additional degree of freedom for controlling ultrafast electron-nuclear dynamics.
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.
This thesis investigates quantum dynamics induced in atoms by ultrashort pulses of light. The work is motivated by recent developments in free-electron lasers, which generate ultrashort pulses of intense, coherent light and enable coherent control of quantum dynamics. We develop theoretical models to study the processes of absorption and emission in laser-atom interactions. Additionally, we study photoionisation, which creates an ion and an electron, and the entanglement that can be generated between these particles. Finally, we have investigated how the spontaneous decay of the ion induces entanglement transfer from the ion-electron pair to the electron-photon pair.This thesis compiles seven papers. Paper I investigates the absorption of light from an attosecond pulse by an atom in a prepared coherent superposition of states. We show how the evolution of the phase of the superposition wave packet influences the attosecond transient absorption spectra. Paper II predicts the existence of Mollow-like triplets in the absorption spectra of strongly coupled atoms. We establish the conditions for the pulse envelope under which this triplet pattern can be supported.Paper III studies two-photon Rabi oscillations, establishing which systems can sustain such dynamics. We find that a two-photon Rabi oscillating system can induce giant counter-rotating oscillations in the population dynamics, enabling investigations of physical effects beyond the rotating-wave approximation.Paper IV studies ionisation from an atom strongly coupled by a dichromatic field, where interference between the two frequency components shapes the temporal symmetry of the atomic dynamics, allowing for coherent control of the photoelectron distribution.Paper V considers an experiment performed at a Free-Electron Laser facility where a helium atom is ionised and the resulting ion is subsequently strongly coupled. The photoelectron spectra are theoretically reproduced and the entanglement between the ion and photoelectron is studied. Paper VI investigates how the entanglement in the ion--electron pair, generated via photoionisation followed by strong coupling, can be coherently controlled by harnessing the time symmetry of the pulse. We find that the observable manifestation of the entanglement can be altered in such a way that the electron energy becomes associated with the ionic state, allowing the entanglement to be detected via coincidence measurements. Paper VII investigates how quantum correlations between the ion and the electron can be coherently controlled by sequential strong coupling of the ion. We find that both the build-up of entanglement and its manifestation can be controlled, and we establish a quantitative measure of the amplitude entanglement that explains the dynamics in an intuitive way. Paper VIII studies the process of entanglement transfer induced by the spontaneous decay of the ion. We find that the ion--electron entanglement generated during the ultrashort interaction with the laser field is transferred to the electron--photon system over the much longer timescale of fluorescence.