We propose a novel method to describe realistically ionization processes with absorbing boundary conditions in basis expansion within the formalism of the so-called Non-Adiabatic Quantum Molecular Dynamics. This theory couples self-consistently a classical description of the nuclei with a quantum mechanical treatment of the electrons in atomic many-body systems. In this paper we extend the formalism by introducing absorbing boundary conditions via an imaginary potential. It is shown how this potential can be constructed in time-dependent density functional theory in basis expansion. The approach is first tested on the hydrogen atom and the pre-aligned hydrogen molecular ion H2+ in intense laser fields where reference calculations are available. It is then applied to study the ionization of non-aligned H2+ and H2. Striking differences in the orientation dependence between both molecules are found. Surprisingly, enhanced ionization is predicted for perpendicularly aligned molecules.
We provide a pedagogical approach to the problem of avoided crossings between electronic molecular curves and to diabatic and adiabatic transitions when the nuclei of a diatomic molecule move according to classical mechanics. For simplicity we restrict the analysis to only two electronic states.
In this supplementary material, we recollect, for reader's convenience, the general scheme of suggested multiscale model (Sec. 1), and basic informations about approaches used for pilot study: a detailed description of the interaction model (Sec. 2) and dynamical methods used for the dark dynamics step (Sec. 3) reported previously in two preceding studies [1, 2]. In addition, a detailed description of the treatment of radiative processes is also given (Sec. 4).
We propose a technique which produces nearly complete ionization of the population of a discrete state coupled to a continuum by a two-photon transition via a lossy intermediate state whose lifetime is much shorter than the interaction duration. We show that using counterintuitively ordered pulses, as in stimulated Raman adiabatic passage (STIRAP), wherein the pulse coupling the intermediate state to the continuum precedes and partly overlaps the pulse coupling the initial and intermediate states, greatly increases the ionization signal and strongly reduces the population loss due to spontaneo…
We show that a laser pulse designed as an adiabatic ramp followed by a kick allows one to reach a perfect postpulse molecular alignment, free of saturation. The mechanism is based on an optimized distribution of the energy between a weakly efficient but non saturating adiabatic ramp and an efficient but saturating impulsive field. Unprecedent degrees of alignment are predicted using state-of-the-art pulse shaping techniques and non-destructive field intensities. The scheme can be extended to reach high degrees of orientation of polar molecules using designed half-cycle pulses.
The alignment dependence of the ionization behavior of H$_2$ exposed to intense ultrashort laser pulses is investigated on the basis of solutions of the full time-dependent Schrödinger equation within the fixed-nuclei and dipole approximation. The total ionization yields as well as the energy-resolved electron spectra have been calculated for a parallel and a perpendicular orientation of the molecular axis with respect to the polarization axis of linear polarized laser pulses. For most, but not all considered laser peak intensities the parallel aligned molecules are easier to ionize. Furthermo…
In this paper we study the response in time of N$_2$, O$_2$ and F$_2$ to laser pulses having a wavelength of 390nm. We find single ionization suppression in O$_2$ and its absence in F$_2$, in accordance with experimental results at $λ= 800$nm. Within our framework of time-dependent density functional theory we are able to explain deviations from the predictions of Intense-Field Many-Body $S$-Matrix Theory (IMST). We confirm the connection of ionization suppression with destructive interference of outgoing electron waves from the ionized electron orbital. However, the prediction of ionization s…
The theoretical investigation of non-adiabatic processes is hampered by the complexity of the coupled electron-nuclear dynamics beyond the Born-Oppenheimer approximation. Classically, the simulation of such reactions is limited by the unfavourable scaling of the computational resources as a function of the system size. While quantum computing exhibits proven quantum advantage for the simulation of real-time dynamics, the study of quantum algorithms for the description of non-adiabatic phenomena is still unexplored. In this work, we propose a quantum algorithm for the simulation of fast non-adi…
The attosecond ultrafast ionization dynamics of correlated two- or many-electron systems have, so far, been mainly addressed investigating atomic systems. In the case of single ionization, it is well known that electron-electron correlation modifies the ionization dynamics and observables beyond the single active electron picture, resulting in effects such as the Auger effect or shake-up/down and knock-up/down processes. Here, we extend these works by investigating the attosecond ionization of a molecular system involving correlated two-electron dynamics, as well as non-adiabatic nuclear dynam…
A theoretical study of the intense-field single ionization of molecular hydrogen or deuterium oriented either parallel or perpendicular to a linear polarized laser pulse (400 nm) is performed for different internuclear separations and pulse lengths in an intensity range of $(2-13)\times10^{13} $W cm$^{-2}$. The investigation is based on a non-perturbative treatment that solves the full time-dependent Schrödinger equation of both correlated electrons within the fixed-nuclei and the dipole approximation. The results for various internuclear separations are used to obtain the ionization yields of…
The measurement of the tunneling time in attosecond experiments, termed attoclock, triggered a hot debate about the tunneling time, the role of time in quantum mechanics, where the interaction with the laser pulse involves two regimes of a different character, the multiphoton and the tunneling (field-) ionization. In the adiabatic field calibration, one of us (O. K.) developed in earlier works a real tunneling time model and showed that the model fits well to the experimental data of Landsmann et al. (Optica {\bf 1}, 343 2014). In the present work, it is shown that the model explains the exper…
The efficiencies of light-harvesting complexes in biological systems can be much higher than the current efficiencies of artificial solar cells. In this paper, we therefore propose and analyse an energy transport mechanism which employs adiabatic passages between the states of an artificially designed antenna molecular system to significantly enhance the conversion of incoming light into internal energy. It is shown that the proposed transport mechanism is relatively robust against spontaneous emission and de-phasing, while also being able to take advantage of collective effects. Our aim is to…
The molecular association process in a thermal gas of $^{85}$Rb is investigated where the effects of the envelope of the radio-frequency field are taken into account. For experimentally relevant parameters our analysis shows that with increasing pulse length the corresponding molecular conversion efficiency exhibits low-frequency interference fringes which are robust under thermal averaging over a wide range of temperatures. This dynamical interference phenomenon is attributed to Stückelberg phase accumulation between the low-energy continuum states and the dressed molecular state which exhibi…
The mass-correction function is evaluated for selected excited states of the hydrogen molecule within a single-state non-adiabatic treatment. Its qualitative features are studied under the avoided crossing of the $EF$ with the $GK$ state and also for the outer well of the $H\bar{H}$ state. For the $H\bar{H}$ state, a negative mass correction is obtained for the vibrational motion near the outer minimum, which accounts for most of the deviation between experiment and earlier theoretical work.
We investigate direct above-threshold ionization in diatomic molecules, with particular emphasis on how quantum interference is altered by a driving field of non-vanishing ellipticity. This interference may be either temporal, i.e., related to ionization events occurring at different times, or spatial, i.e., related to the electron emission at different centers in the molecule. Employing the strong-field approximation and saddle-point methods, we find that, in general, for non-vanishing ellipticity, there will be a blurring of the temporal and spatial interference patterns. The former blurring…
We introduce the coherent state mapping ring-polymer molecular dynamics (CS-RPMD), a new method that accurately describes electronic non-adiabatic dynamics with explicit nuclear quantization. This new approach is derived by using coherent state mapping representation for the electronic degrees of freedom (DOF) and the ring-polymer path-integral representation for the nuclear DOF. CS-RPMD Hamiltonian does not contain any inter-bead coupling term in the state-dependent potential, which is a key feature that ensures correct electronic Rabi oscillations. Hamilton's equation of motion is used to sa…
We derive the non-adiabatic ring polymer molecular dynamics (RPMD) approach in the phase space of the SU(N) Lie Group. This method, which we refer to as the spin mapping non-adiabatic RPMD (SM-NRPMD), is based on the spin-mapping formalism for the electronic degrees of freedom (DOFs) and ring polymer path-integral description for the nuclear DOFs. Using the Stratonovich-Weyl transform for the electronic DOFs, and the Wigner transform for the nuclear DOFs, we derived an exact expression of the Kubo-transformed time-correlation function (TCF). We further derive the spin mapping non-adiabatic Mat…
Collective two-color photoassociation of a freely-interacting 87Rb Bose-Einstein condensate is theoretically examined, focusing on stimulated Raman adiabatic passage (STIRAP) from an atomic to a stable molecular condensate. In particular, Drummond et al. [Phys. Rev. A 65, 063619 (2002); cond-mat/0110578] have predicted that particle-particle interactions can limit the efficiency of collective atom-molecule STIRAP, and that optimizing the laser parameters can partially overcome this limitation. We suggest that the molecular conversion efficiency can be further improved by treating the initial c…
We examine collective magnetoassociation of a Bose-Einstein condensate (BEC), focusing on rapid adiabatic passage from atoms to molecules induced by a sweep of the magnetic field across a wide (>~ 10 G) Feshbach resonance in 85Rb. This problem raises an interest because strong magnetoassociation is expected to favor the creation of molecular-dissociated atom pairs over the formation of molecular BEC [Javanainen and Mackie, Phys. Rev. Lett. 88, 090403 (2002)]. Nevertheless, the conversion to atom pairs is found to depend on the direction of the sweep, so that a system initially above threshold …
