Quantum electronic coherences by attosecond transient absorption spectroscopy: ab initio B-spline RCS-ADC study

Abstract

Here I present a fully ab initio time-resolved study of X-ray attosecond transient absorption spectroscopy (ATAS) in a prototypical polyatomic molecule, pyrazine, and demonstrate the possibility of retrieving the many-electron...

Dialogue on analytical and ab initio methods in attoscience

“…Nevertheless, they often require significant extensions to work well in attoscience, particularly regarding how the ionised continuum is handled. Recent examples of these extensions include ab initio methods based on the algebraic diagrammatic construction (ADC) [31][32][33][34][35] and its restricted-correlation-space extension (RCS-ADC) [36][37][38][39], multi-reference configuration interaction (MRCI) [40,41], and multi-configuration timedependent Hartree [42] and Hartree-Fock [43] methods, as well as restricted-active-space self-consistent-field (RAS-SCF) [44][45][46] approaches. -Basis-set development is another crucial element of the numerical implementation work for ab initio methods in attoscience, since the physics accessible to the method, as well as its computational cost, are often determined by the basis set in use.…”

“…-Basis-set development is another crucial element of the numerical implementation work for ab initio methods in attoscience, since the physics accessible to the method, as well as its computational cost, are often determined by the basis set in use. Recent work on basis sets includes the development of B-spline functions, both on their own [31][32][33][34][35][36][37][38][39]47], and in hybrid combinations with Gaussian-type orbitals (GTOs) [44][45][46], as well as finite-difference approaches [48][49][50], finite-element discrete-variable-representation functions [51,52], grid-based methods [53,54], and simple plane-waves [55].…”

Entanglement of Orbital Angular Momentum in Non-Sequential Double Ionization

“…As early as 1994, a correlation measure, which provides an indication of entanglement based on Schmidt decomposition, was developed [24]. Many studies have focused on entanglement between photoelectrons and ions [25][26][27][28][29][30][31], which is an essential part of understanding decoherence [32], while other studies have focused on electronelectron entanglement [33][34][35]. However, all these previous studies involved the calculation of a continuous variable density matrix and the consideration of entanglement measures such as the purity [27,29,30,34,35], von Neumann entropy [27][28][29]35] or a Schmidt decomposition based measure [24,33].…”

“…Many studies have focused on entanglement between photoelectrons and ions [25][26][27][28][29][30][31], which is an essential part of understanding decoherence [32], while other studies have focused on electronelectron entanglement [33][34][35]. However, all these previous studies involved the calculation of a continuous variable density matrix and the consideration of entanglement measures such as the purity [27,29,30,34,35], von Neumann entropy [27][28][29]35] or a Schmidt decomposition based measure [24,33]. These quantities, when derived from continuous variables, have some drawbacks: (i) They are a considerable challenge to compute, and often approximations or restrictions must be imposed, such as one-dimensional calculations.…”

Simulating weak-field attosecond processes with a Lanczos reduced basis approach to time-dependent equation of motion coupled cluster theory

“…Despite these early endeavours, real-time methods did not become practical at that time due to the lack of electron correlation effects at the Hartree-Fock level and the high computational cost associated with propagation of correlated wave functions. However, decades of steady advancements in computing power and numerical algorithms have led to a renewed interest in explicit time propagation in correlated methods like density functional theory [12,13], multiconfigurational selfconsistent-field [14][15][16], configuration interaction [17][18][19][20], algebraic diagrammatic construction [21,22] and coupledcluster [23][24][25][26][27][28][29][30][31][32][33].…”