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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 Abstract

An extensive study of photoionization from neon excited states was performed. The R-matrix approach was applied to calculate a photoionization cross-section from the metastable 2p5(2PJf)3s[K]0,2 and dipole-allowed 2p5(2PJf)3s[K]1 states. The resonance structures and Cooper minimum accessible in photoionization from the excited states by the photons with energy below 30 eV were analyzed. The parameters of the lowest autoionizing states (AISs) of even parity were extracted by fitting of the photoionization cross-section. For the dipole-allowed states, calculations are presented for unpolarized, linearly and circularly polarized radiation.

Attosecond transient absorption spectroscopy (ATAS) allows for the study of electron dynamics in atoms and molecules with attosecond time resolution. Previous works reported in the literature have made use of ATAS to image and control such dynamics in the single-channel ionization continuum of helium; in particular, in the vicinity of the doubly excited autoionizing states lying between the N=1 and N=2 thresholds. In this work, we have extended these studies to autoionizing states lying above the N=2 threshold, where several ionization channels are open. From an accurate solution of the time-dependent Schrödinger equation, we predict the appearance of pronounced one-photon beatings between the 3snp states and the adjacent 1Se and 1De resonances, as well as, more surprisingly, two-photon beatings between the 3s3p doubly excited state and the 1Po nonresonant continuum. Both effects lead to a significant distortion of the 3snp Fano profiles and to a strong variation of these profiles with the pump-probe delay, thus demonstrating control of the corresponding multichannel two-electron correlated wave packets, in the same way as reported for resonances lying below the N=2 threshold, We would like to acknowledge allocation of computer time at Mare Nostrum BSC and CCC-UAM. This work was supported by the European Research Council Advanced Grant No. XCHEM 290853, the MINECO Projects No. FIS2013-42002-R and No. FIS2016-77889-R, the European COST Action XLIC CM1204, and the CAM project NANOFRONTMAG. L.A. acknowledges support from the TAMOP NSF Grant No. 1607588, as well as UCF fundings

We present a theoretical study of the photoelectron attosecond beating due to interference of two-photon transitions in the presence of autoionizing states. We show that, as a harmonic traverses a resonance, both the phase shift and frequency of the sideband beating significantly vary with photon energy. Furthermore, the beating between two resonant paths persists even when the pump and the probe pulses do not overlap, thus providing a nonholographic interferometric means to reconstruct coherent metastable wave packets. We characterize these phenomena by means of a general analytical model that accounts for the effect of both intermediate and final resonances on two-photon processes. The model predictions are in excellent agreement with those of accurate ab initio calculations for the helium atom in the region of the N=2 doubly excited states, We acknowledge computer time from the CCCUAM and Marenostrum Supercomputer Centers and financial support from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No. 290853 XCHEM, the MINECO Project No. FIS2013-42002-R, the ERA-Chemistry Project No. PIM2010EEC-00751, and the European COST Action XLIC CM1204

Inelastic processes occurring under electron impact with ions of II and III groups of the Periodic Table of the Chemical Elements were investigated. The mechanisms of these processes are shown to become essentially complicated depending on the complexity of the ion electron structure. The role of relativistic and correlation effects in the multielectron ion electron shells increases, and as a result the probability ratio of the radiative and electron channels of the autoionizing states decay is changed, the role of resonance processes (resonance excitation and dielectronic recombination) in the course of inelastic processes increases as well., Исследованы неупругие процессы, протекающие при столкновениях электронов с ионами II и III групп Периодической системы химических элементов. Показано, что механизмы этих процессов значительно усложняются в зависимости от сложности электронного строения ионов. В электронных оболочках многоэлектронных ионов возрастает роль релятивистских и корреляционных эффектов, и, как следствие, изменяется соотношение вероятностей радиационного и электронного каналов распада автоионизационных состояний, а также увеличивается роль резонансных процессов (резонансного возбуждения и диэлектронной рекомбинации) в протекании неупругих процессов., Досліджено непружні процеси, що мають місце при зіткненні електронів з іонами II і III груп Періодичної системи хімічних елементів. Показано, що механізми цих процесів значно ускладнюються в залежності від складності електронної будови іонів. В електронних оболонках багатоелектронних іонів зростає роль релятивістських і кореляційних ефектів, і, як наслідок, змінюється співвідношення ймовірності радіаційного та електронного каналів розпаду автоіонізаційних станів, збільшується вплив резонансних процесів (резонансного збудження та діелектронної рекомбінації) на перебіг непружних процесів.

Excited states of atoms and molecules lying above the ionization threshold can decay by electron emission in a process commonly known as autoionization. The autoionization widths can be calculated conveniently using Fano formalism and discretized atomic and molecular spectra by a standard procedure referred to as Stieltjes imaging. The Stieltjes imaging procedure requires the use of the full discretized spectrum of the final states of the autoionization, making its use for poly-atomic systems described by high-quality basis sets impractical. Following our previous work on photoionization cross-sections, here we show that also in the case of autoionization widths, the full diagonalization bottleneck can be overcome by the use of Lanczos pseudospectra. We test the proposed method by calculating the well-documented autoionization widths of inner-valence-excited neon and apply the new technique to autoionizing states of hydrofluoric acid and benzene.