arXiv subjects

Nikolay V. Golubev

Publications and source records attributed to Nikolay V. Golubev.

16 recordsLinked to original sources

arXiv2026

Unified approach to time-resolved x-ray and electron diffraction imaging

Time-resolved x-ray diffraction (TR-XRD) and ultrafast electron diffraction (TR-UED) are emerging tools for probing ultrafast quantum dynamics. From a theoretical perspective, they are commonly described within different frameworks and modeled using distinct approximations. Here, we present a unified quantum-field-based description of ultrafast diffraction imaging that permits consistent consideration of TR-XRD and TR-UED within a common theoretical formalism. Our approach elucidates the correspondence between TR-XRD and TR-UED and allows their similarities and differences to be systematically disentangled. The developed formalism is sufficiently general to consistently and straightforwardly incorporate additional physical effects of interest, such as relativistic charge-current and current-current couplings. We apply our approach to simulate diffraction measurements of laser-driven electron dynamics in graphene, demonstrating the unique capabilities of diffraction imaging to unravel intricate quantum processes in matter.

quant-ph↗

arXiv2026

Control of valence-electron motion in Xe cations using the stimulated-Raman-adiabatic-passage technique

This work theoretically investigates possibilities of using the Stimulated Raman Adiabatic Passage (STIRAP) and its variants to control a coherent superposition of quantum states. We present a generalization of the so-called fractional STIRAP (f-STIRAP), demonstrating precise control over the mixing ratio of quantum states in the wave packet. In contrast to conventional f-STIRAP, designed to drive a system from an eigenstate into a coherent superposition, our scheme enables arbitrary control over the composition of an already existing superposition state. We demonstrate that an approximate version of this technique -- where analytically designed laser pulses with composite envelopes are replaced by simple Gaussian pulses -- achieves comparable performance in controlling the dynamics of the wave packet. A limiting case of this scheme, utilizing two pulses with identical Gaussian envelopes and tuned delay and relative phase, is also explored, revealing experimentally accessible pathways for manipulating quantum coherence. We apply our developed techniques to control the ultrafast charge migration in the spin-orbit split ground electronic states of xenon cation via intermediate valence- and core-excited states. Finally, we propose concrete experimental realizations of the developed control schemes in combination with attosecond transient absorption spectroscopy as a method to probe the system.

quant-ph↗

arXiv2025

Quantum attomicroscopy: imaging quantum chemistry in action

How quantum electron and nuclei motions affect biomolecular chemical reactions remains a central challengeable question at the interface of quantum chemistry and biology. Ultrafast charge migration in deoxyribonucleic acid (DNA) has long been hypothesized to play a critical role in photochemistry, genome stability, and long-range biomolecular signaling, however, direct real-time observation of these electronic processes has remained elusive. Here, we present a theoretical investigation and propose the concept of future experimental measurements of laser-driven charge dynamics in the canonical DNA nucleobase pairs thymine_adenine and cytosine_guanine. Attosecond-resolved simulations employing high-level ab initio methods reveal base-dependent ionization mechanisms, directional charge migration pathways, and electronic coherences that govern sub-femtosecond redistribution of electron density across hydrogen-bonded nucleobase interfaces. Accordingly, we propose the concept of a quantum attosecond scanning electron microscope, termed the quantum attomicroscope (Q-attomicroscope), a capable of imaging photoinduced quantum chemistry reactions in attosecond temporal resolution and sub-nanometer spatial precision. As a proof of principle, we propose to image the charge migrations dynamics in DNA which we studied theoretically. Together, our preceptive bridges theory, instrumentation, and control, outlining a pathway toward laser mediated manipulation of DNA structure with implications for repair processes, chemical reactivity, and future personalized medicine.

physics.chem-ph↗

arXiv2025

Attosecond Transient Absorption Study of Coherent Hole Oscillation in Ar+

We report on the observation, characterization, and control of the electron dynamics in ionized argon atoms. We utilized an intense mid-infrared (MIR) pulse to create a coherent superposition of the spin-orbit split ground state of the ion. A weak extreme ultraviolet (XUV) pulse then probes the hole oscillation through time-resolved transient absorption spectroscopy. We investigated several 3p to nd transitions accessible with our XUV high harmonics which show a 23fs beat corresponding to the energy separation between the initially populated states. The experimental attosecond transient absorption signals for different pathways were simulated using detailed TDSE simulations and perturbative analytic calculations. The analysis of phase relations between the oscillations reveals important information about transition dipole moments in the system. In addition, we employed another strong MIR pulse to achieve transient control over the absorption by inducing Stark shifts of the states without affecting the electronic coherences.

physics.atom-ph↗

arXiv2025

Comment on "Comment on Attosecond electron microscopy and diffraction"

Over the past few decades, following the first demonstration of ultrafast electron microscopy, numerous research groups have focused on achieving attosecond temporal resolution in electron microscopy with the goal of imaging electron and atomic motion. Recently, several studies have claimed to achieve attosecond temporal resolution in imaging(1-3). These claims are based on the generation of attosecond electron pulse trains. However, in typical time-resolved measurements used to capture dynamic processes in real-time, the temporal resolution is determined by the envelope of the pulse train. The reliance of using attosecond electron pulse trains fails to account for the distinct temporal resolution advantages enabled by our attosecond optical gating, which are absent in the case of using a continuous-wave or long laser pulse. These oversights highlight the limitations of this methodology (1-3) in studying ultrafast phenomena of matter. It is crucial to clarify this distinction to avoid confusion, misinterpretation, and potential miscitations within the community regarding attosecond temporal resolution in electron microscopy and the attosecond imaging of matter dynamics. In contrast, Hui et al. (4) present the first realistic demonstration of attosecond imaging resolution in electron microscopy, enabling the diffraction imaging of electron motion dynamics in graphene. In a commentary by Peter Baum and Claus Ropers, the authors conjecture that the graphene dynamics observed in our time-resolved diffraction experiment (Fig. 5, Hui et al. 2024) (4) is an optical interference artifact or light modulation of electrons effects, similar to what was reported previously (1-3), in addition to raising other technical concerns. In this reply, we are pleased to address these allegations and provide clarifications to resolve the raised technical questions.

physics.optics↗

arXiv2025

Can increasing the size and flexibility of a molecule reduce decoherence and prolong charge migration?

Coherent superposition of electronic states, created by ionizing a molecule, can initiate ultrafast dynamics of the electron density. Correlation between nuclear and electron motions, however, typically dissipates the electronic coherence in only a few femtoseconds, especially in larger and more flexible molecules. We, therefore, use ab initio semiclassical dynamics to study decoherence in a sequence of analogous organic molecules of increasing size and find, surprisingly, that extending the carbon skeleton in propynal analogs slows down decoherence and prolongs charge migration. To elucidate this observation, we decompose the overall decoherence into contributions from individual vibrational modes and show that: (1) The initial decay of electronic coherence is caused by high- and intermediate-frequency vibrations via momentum separation of nuclear wavepackets evolving on different electronic surfaces. (2) At later times, the coherence disappears completely due to the increasing position separation in the low-frequency modes. (3) In agreement with another study, we observe that only normal modes that preserve the symmetry of the molecule induce decoherence. All together, we justify the enhanced charge migration by a combination of increased hole-mixing and the disappearance of decoherence contributions from specific vibrational modes: CO stretching in butynal and various H rockings in pentynal.

quant-ph↗

arXiv2024

Attosecond Diffraction Imaging of Electron Dynamics in Solids

Visualizing the electron dynamics in four dimensions of space and time is crucial to the understanding of several ubiquitous processes in nature. Hence, ultrafast X-ray and electron imaging tools have been developed to probe the dynamics of matter by means of the time-resolved diffraction imaging (TRDI). In this work, we report an extension of the theory underlying the TRDI to the case of the laser-driven electron dynamics in solid state systems. We demonstrate that the TRDI signal encodes essential information about the time-dependent electron density of the system under study and thus makes it possible to decipher the ultrafast quantum dynamics and the electron transfer phenomena in solids. We apply the developed approach to image the laser-driven electron dynamics in neutral graphene showing that the predictions made by the fully quantum version of the TRDI deviate significantly from those obtained with the conventional semiclassical approach.

cond-mat.mes-hall↗

arXiv2024

Attomicroscopy imaging and control of electron motion in graphene

Attosecond science has leveraged the highly nonlinear interactions between intense few-cycle laser pulses and matter, allowing for unprecedented observation and control of electron motion with remarkable temporal resolution. However, most existing experiments focusing on laser-controlled attosecond dynamics have dealt with quasi-bound electrons released in the ionization continua of atoms, molecules, or conduction bands in solid-state systems. Here, we employed the recently developed attomicroscopy imaging tool to investigate, visualize, and manipulate the motion of bound electrons in graphene. By adjusting the carrier-envelope phase and the field strength of the driving electric field, we were able to control both the amplitude and direction of the field-induced electron current between carbon atoms in graphene. This research opens new avenues for understanding and controlling dynamic, on-demand electron motion processes, including chemical reactions, molecular bonding, and the electronic properties of materials.

cond-mat.mes-hall↗

arXiv2023

Attosecond Electron Microscopy

The electron motion in atoms and molecules is at the heart of all phenomena in nature that occur outside the nucleus. Recently, ultrafast electron and X-ray imaging tools have been developed to image the ultrafast dynamics of matter in real time and space. The cutting-edge temporal resolution of these imaging tools is on the order of a few tens to a hundred femtoseconds, limiting imaging to atomic dynamics. Hence electron motion imaging remains beyond the reach. Here, we achieved attosecond electron imaging temporal resolution in a transmission electron microscope, orders of magnitude faster than the highest reported imaging resolution, to demonstrate, which we coin it as (attomicroscopy) to image the field-induced electron dynamics in neutral multilayer graphene. Our results show that the electron motion between the carbon atoms in graphene is due to the field-driven electron dynamics in the conduction band and depends on the field waveform, strength, and polarization direction. This attomicroscopy imaging provides more insights into the electron motion of neutral matter in real time and space and would have long-anticipated real-life attosecond science applications in quantum physics, chemistry, and biology.

physics.optics↗

arXiv2023

How to find molecules with long-lasting charge migration?

Under certain conditions, the ionization of a molecule may create a superposition of electronic states, leading to ultrafast electron dynamics. If controlled, this motion could be used in attochemistry applications, but it has been shown that the decoherence induced by the nuclear motion typically happens in just a few femtoseconds. We recently developed an efficient algorithm for finding molecules exhibiting long-lasting electronic coherence and charge migration across the molecular structure after valence ionization. Here, we first explain why the but-3-ynal molecule is a promising candidate to study this type of ultrafast electron dynamics. Then, we use the 3-oxopropanenitrile molecule, which does not show long-lasting charge migration in any of three different ionization scenarios, as an example demonstrating that several different properties must be fulfilled simultaneously to make the attochemistry applications possible.

physics.chem-ph↗

arXiv2022

Efficient Semiclassical Evaluation of Electronic Coherences in Polyatomic Molecules

Exposing a molecule to intense light pulses may bring this molecule to a nonstationary quantum state, thus launching correlated dynamics of electronic and nuclear subsystems. Although much had been achieved in the understanding of fundamental physics behind the electron-nuclear interactions and dynamics, accurate numerical simulations of light-induced processes taking place in polyatomic molecules remain a formidable challenge. Here, we review a recently developed theoretical approach for evaluating electronic coherences in molecules, in which the ultrafast electronic dynamics is coupled to nuclear motion. The presented technique, which combines accurate ab initio on-the-fly simulations of electronic structure with efficient semiclassical procedure to compute the dynamics of nuclear wave packets, is not only computationally efficient, but also can help shed light on the underlying physical mechanisms of decoherence and revival of the electronic coherences driven by nuclear rearrangement.

physics.chem-ph↗

arXiv2021

Search for long lasting electronic coherence using on-the-fly ab initio semiclassical dynamics

Using a combination of high-level ab initio electronic structure methods with efficient on-the-fly semiclassical evaluation of nuclear dynamics, we performed a massive scan of small polyatomic molecules searching for a long lasting oscillatory dynamics of the electron density triggered by the outer-valence ionization. We observed that in most of the studied molecules, the sudden removal of an electron from the system either does not lead to the appearance of the electronic coherence, or the created coherences become damped by the nuclear rearrangement on a time scale of a few femtoseconds. However, we report several so far unexplored molecules with the electronic coherences lasting up to 10 fs which can be good candidates for experimental studies. In addition, we present the full-dimensional simulations of the electronic coherences coupled to nuclear motion in several molecules which were studied previously only in the fixed nuclei approximation.

physics.chem-ph↗

arXiv2021

Core-valence attosecond transient absorption spectroscopy of polyatomic molecules

Tracing ultrafast processes induced by interaction of light with matter is often very challenging. In molecular systems, the initially created electronic coherence becomes damped by the slow nuclear rearrangement on a femtosecond timescale which makes real-time observations of electron dynamics in molecules particularly difficult. In this work, we report an extension of the theory underlying the attosecond transient absorption spectroscopy (ATAS) for the case of molecules, including a full account for the coupled electron-nuclear dynamics in the initially created wave packet, and apply it to probe the oscillations of the positive charge created after outer-valence ionization of the propiolic acid molecule. By taking advantage of element-specific core-to-valence transitions induced by X-ray radiation, we show that the resolution of ATAS makes it possible to trace the dynamics of electron density with atomic spatial resolution.

physics.chem-ph↗

arXiv2020

On-the-fly ab initio semiclassical evaluation of electronic coherences in polyatomic molecules reveals a simple mechanism of decoherence

Irradiation of a molecular system by an intense laser field can trigger dynamics of both electronic and nuclear subsystems. The lighter electrons usually move on much faster, attosecond time scale but the slow nuclear rearrangement damps ultrafast electronic oscillations, leading to the decoherence of the electronic dynamics within a few femtoseconds. We show that a simple, single-trajectory semiclassical scheme can evaluate the electronic coherence time in polyatomic molecules accurately by demonstrating an excellent agreement with full-dimensional quantum calculations. In contrast to numerical quantum methods, the semiclassical one reveals the physical mechanism of decoherence beyond the general blame on nuclear motion. In the propiolic acid, the rate of decoherence and the large deviation from the static frequency of electronic oscillations are quantitatively described with just two semiclassical parameters---the phase space distance and signed area between the trajectories moving on two electronic surfaces. Because it evaluates the electronic structure on the fly, the semiclassical technique avoids the "curse of dimensionality" and should be useful for preselecting molecules for experimental studies.

physics.chem-ph↗

arXiv2015

Control of charge migration in molecules by ultrashort laser pulses

Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme for control of the charge migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and an amine moieties that simple pulses can be used for stopping the charge-migration oscillations and localizing the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

physics.chem-ph↗

arXiv2014

Control of populations of two-level systems by a single resonant laser pulse

We present a simple approach allowing to obtain analytical expressions for laser pulses that can drive a two-level system in an arbitrarily chosen way. The proposed scheme relates every desired population-evolution path to a single resonant laser pulse. It allows to drive the system from any initial superposition of the two states to a final state having the desired distribution of the populations. We exemplify the scheme with a concrete example, where the system is driven from a non-stationary superposition of states to one of its eigenstates. We argue that the proposed approach may have interesting applications for designing pulses that can control ultrafast charge-migration processes in molecules. Although focused on laser driven population control, the results obtained are general and could be applied for designing other types of control fields.

quant-ph↗