External Time-dependent Electric Field Research Articles

Cavity-modified molecular dipole switching dynamics.

Polaritonic states, which are formed by resonances between a molecular excitation and the photonic mode of a cavity, have a number of useful properties that offer new routes to control molecular photochemistry using electric fields. To provide a theoretical description of how polaritonic states affect the real-time electron dynamics in molecules, a new method is described where the effects of strong light-molecule coupling are implemented using real-time electronic structure theory. The coupling between the molecular electronic states and the cavity is described by the Pauli-Fierz Hamiltonian, and transitions between polaritonic states are induced via an external time-dependent electric field using time-dependent configuration interaction (TDCI) theory, producing quantum electrodynamics TDCI (QED-TDCI). This method is used to study laser-induced ultrafast charge transfer and dipole-switching dynamics of the LiCN molecule inside a cavity. The increase in cavity coupling strength is found to have a significant impact on the energies and transition dipole moments of the molecule-cavity system. The convergence of the polaritonic state energies as a function of the number of included electronic and photonic basis states is discussed.

Optimal control of a semiclassical Boltzmann equation for charge transport in graphene

An ensemble optimal control problem governed by a semiclassical space-homogeneous Boltzmann equation for charge transport in graphene is formulated and analyzed.The control mechanism is an external time-dependent electric field having the purpose of driving the material density of electrons in graphene to follow a desired trajectory. For this purpose, an ensemble cost functional with quadratic H1 costs is considered.Well-posedness of the control problem is proved, and the characterization of optimal controls by an optimality system is discussed. This system is approximated by a discontinuous Galerkin scheme and solved using a nonlinear conjugate gradient method. Results of numerical experiments are presented that demonstrate the ability of the proposed control framework to design control fields.

Photodetachment microscopy with double pulse in time-dependent fields

We present the photodetachment microscopy of the singly charged negative ions using the double pulse with a frequency near the ionization threshold in the presence of the time-dependent external electric field. In the presence of time-dependent electric field, the number of photoelectron trajectories contributing to the electron flux at a space–time point at the detector may be more than two. We demonstrate that the relative flight times of the classical trajectories, to reach a point at the detector plane can be calculated by observing the photoelectron flux at a particular time at the detector and scanning the second pulse by varying the time delay between the two coherent laser pulses. Moreover, investigating the photoelectron flux, we have found that the flux distribution can be controlled by the relative phase difference between the two coherent pulses separated by a short time delay, at spatial and temporal points where the classical trajectories associated with photoelectron emerging at different pulses arrive at the detector simultaneously and exhibit interference. The temporal and spatial photoelectron flux distribution oscillates as a function of the relative phase difference between the pulses. The time-dependent quantum propagator approach with stationary phase approximation is linked analytically with the time-dependent closed orbit theory.

Electroosmotic flow of Maxwell fluid in a microchannel of isosceles right triangular cross section

This work is presented to study the unsteady oscillatory electroosmotic flow of Maxwell fluid in a microchannel of an isosceles right triangular cross section. An external time-dependent electric field is applied and high zeta potential conditions are considered. Due to the difficulty of theoretical solution, a numerical method is adopted. The numerical solutions are derived by employing the finite difference method. Finally, the effects of some dimensionless variables, the relaxation time, the angular Reynolds number, the wall zeta potential, and the ratio between the typical length and the Debye length on the velocity profiles, are interpreted graphically.

Vacuum instability in time-dependent electric fields: New example of an exactly solvable case

A new exactly solvable case in strong-field quantum electrodynamics with a time-dependent external electric field is presented. The corresponding field is given by an analytic function, which is asymmetric (in contrast to Sauter-like electric field) with respect to the time instant, where it reaches its maximum value, that is why we call it the analytic asymmetric electric field. We managed to exactly solve the Dirac equation with such a field, which made it possible to calculate characteristics of the corresponding vacuum instability nonperturbatively. We construct the so-called in- and out-solutions and with their help calculate mean differential and total numbers of created charged particles, probability of the vacuum to remain a vacuum, vacuum mean values of current density and energy-momentum tensor of the particles. We study the vacuum instability in regimes of rapidly and slowly changing analytic asymmetric electric field, and compare the obtained results with corresponding ones obtained earlier for the case of the symmetric Sauter-like electric field. We also compare exact results in the regime of slowly changing field with corresponding results obtained within the slowly varying field approximation recently proposed by two of the authors, thus demonstrating the effectiveness of such an approximation.

Electric-field dissociation of weakly bound molecular ions

We present a full quantal study on the dissociation of a weakly bound molecular ion in the presence of an external time-dependent electric field. We focus on the dissociation dynamics of a molecular ion in a Paul trap relevant for atom-ion hybrid traps. Our results show that a weakly bound molecular ion survives in a Paul trap giving a theoretical ground to previous experimental findings [A. Kr\"ukow et al. Phys. Rev. Lett. 116, 193201 (2016) and A. Mohammadi et al. Phys. Rev. Research 3, 013196 (2021)]. In particular, we find that weakly bound molecular ions are more likely to survive in traps with large RF frequency. Similarly, we show that applying an electric field ramp is an efficient method to state-selectively detect weakly bound molecular ions, analogous to the well-known selective field ionization technique applied in Rydberg atoms, that it may also be used to detect these species in atom-ion hybrid traps.

Giant Linear and Nonlinear Excitonic Responses in an Atomically Thin Indirect Semiconductor Nitrogen Phosphide

Large linear and nonlinear optical responses can be obtained from two-dimensional semiconductors with an indirect electronic gap. Here, we demonstrate exceptionally large exciton-driven responses such as the fundamental exciton binding energy (2 eV), zero-point band-gap renormalization (200 meV), and nonlinear second and third harmonic coefficients (800 pm/V and 1.4 × 10–18 m2/V2, respectively) from an atomically thin binary group-V nitrogen phosphide (NP) semiconductor. The influence of lattice vibrations on the absorption spectra unfolds strong electronic couplings to both LA and ZO-TO phonon modes. All the linear process analyses were computed using a fully ab initio-based G0W0 + Bethe–Salpeter equation approach that also includes the electron–phonon self-energies. The nonlinear processes were instead obtained using a real-time ab initio process flow after creating a coupling between the time-dependent external electric field and the correlated electrons within the modern theory of polarization and the same electron–hole interaction level.

External-field-induced dynamics of a charged particle on a closed helix.

We investigate the dynamics of a charged particle confined to move on a toroidal helix while being driven by an external time-dependent electric field. The underlying phase space is analyzed for linearly and circularly polarized fields. For small driving amplitudes and a linearly polarized field, we find a split up of the chaotic part of the phase space, which prevents the particle from inverting its direction of motion. This allows for a nonzero average velocity of chaotic trajectories without breaking the well-known symmetries commonly responsible for directed transport. Within our chosen normalized units, the resulting average transport velocity is constant and does not change significantly with the driving amplitude. A very similar effect is found in case of the circularly polarized field and low driving amplitudes. Furthermore, when driving with a circularly polarized field, we unravel a second mechanism of the split up of the chaotic phase space region for very large driving amplitudes. There exists a wide range of parameter values for which trajectories may travel between the two chaotic regions by crossing a permeable cantorus. The limitations of these phenomena, as well as their implication on manipulating directed transport in helical geometries are discussed.

Quantum Photonic Simulation of Spin-Magnetic Field Coupling and Atom-Optical Field Interaction

In this work, we present the physical simulation of the dynamical and topological properties of atom-field quantum interacting systems by means of integrated quantum photonic devices. In particular, we simulate mechanical systems used, for example, for quantum processing and requiring a very complex technology such as a spin-1/2 particle interacting with an external classical time-dependent magnetic field and a two-level atom under the action of an external classical time-dependent electric (optical) field (light-matter interaction). The photonic device consists of integrated optical waveguides supporting two collinear or codirectional modes, which are coupled by integrated optical gratings. We show that the single-photon quantum description of the dynamics of this photonic device is a quantum physical simulation of both aforementioned interacting systems. The two-mode photonic device with a single-photon quantum state represents the quantum system, and the optical grating corresponds to an external field. Likewise, we also present the generation of Aharonov–Anandan geometric phases within this photonic device, which also appear in the simulated systems. On the other hand, this photonic simulator can be regarded as a basic brick for constructing more complex photonic simulators. We present a few examples where optical gratings interacting with several collinear and/or codirectional modes are used in order to illustrate the new possibilities for quantum simulation.

Exciton-driven giant nonlinear overtone signals from buckled hexagonal monolayer GaAs

We report here a giant $\left|\chi_{baa}^{2}\right|=$780 pm/V second harmonic and $\left|\chi_{aaaa}^{3}\right|=$1.4$\times$10$^{-17}$ m$^{2}$/V$^{2}$ third harmonic signal from single atomic sheet of buckled hexagonal GaAs. We demonstrate this through the solution of an ab-initio real-time Bethe-Salpeter equation by including the electron-hole screened-exchange self-energy. The coupling between time-dependent external electric field and correlated electrons is treated within the modern theory of polarization. The result of our calculation envisage monolayer GaAs to be a prominent member in the material library of non-linear signal generations.

Slippage Effect on the Oscillatory Electroosmotic Flow of Power-Law Fluids in a Microchannel

The oscillatory electroosmotic flow (OEOF) under the influence of the Navier slip condition in power law fluids through a microchannel is studied numerically. A time-dependent external electric field (AC) is suddenly imposed at the ends of the microchannel which induces the fluid motion. The continuity and momentum equations in the and direction for the flow field were simplified in the limit of the lubrication approximation theory (LAT), and then solved using a numerical scheme. The solution of the electric potential is based on the Debye-Hückel approximation which suggest that the surface potential is small, say, smaller than 0:025V and for a symmetric () electrolyte. Our results suggest that the velocity profiles across the channel-width are controlled by the following dimensionless parameters: the dimensionless slip length , the Womersley number, , the electrokinetic parameter, , defined as the ratio of the characteristic length scale to the Debye length, the parameter which represents the ratio of the Helmholtz-Smoluchowski velocity to the characteristic length scale and the flow behavior index, . Also, the results reveal that the velocity magnitude gets higher values as increases and become more and more nonuniform across the channel-width as the and are increased, so OEOF can be useful in micro-fluidic devices such as micro-mixers.

Analytical solutions for unsteady electrohydrodynamics flows of Maxwell fluids in microchannels with circular cross section

Unsteady electrohydrodynamic flow of Maxwell fluids through a microchannel with a circular cross section under the influence of a time-dependent external electric field is studied in the Debye–Hückel approximation. Analytical solutions for electric potential of charge distribution, fluid velocity, and the components of a shear stress tensor are determined by using a suitable integral transform regarding the azimuthal variable, the Laplace transform with respect to the time variable, and the finite Hankel transform regarding the radial coordinate. Flows caused by an oscillating electric field have been studied as a particular case of the general model. The analytical solutions corresponding to the flow of Newtonian fluids have also been obtained as particular cases of analytical solutions of the Maxwell fluid flow. Numerical values of the analytical solutions are obtained using the MathCAD15 software. The profiles of electric potential and fluid velocity are presented in two/three-dimensional graphical illustrations.

How To Excite Nuclear Wavepackets into Electronically Degenerate States in Spin-Vibronic Quantum Dynamics Simulations.

The excited-state dynamics of two functional Fe-carbene complexes, [Fe(bmip)2]2+ (bmip = 2,6-bis(3-methyl-imidazole-1-ylidene)-pyridine) and [Fe(btbip)2]2+ (btbip = 2,6-bis(3- tert-butyl-imidazole-1-ylidene)pyridine), are studied using the spin-vibronic model. In contrast to the usual projection of the ground state nuclear wave function onto an excited state surface, the dynamics are initiated by an explicit interaction term between the external time-dependent electric field (laser pulse) and the transition dipole moment of the molecule. The results show that the spin-vibronic model, as constructed directly from electronic structure calculations, exhibits erroneous, polarization-dependent relaxation dynamics stemming from artificial interference of coupled relaxation pathways. This is due to the lack of rotational invariance in the description of excitation into degenerate states. We introduce and discuss a correction using the spherical basis and complex transition dipole moments. This modification in the interaction Hamiltonian leads to rotationally invariant excitation and produces polarization-independent population dynamics.

Characterization of ZnO as substrate for DSSC.

We present a complete analysis of the photoinjection process in 3 nm spherical ZnO nanoparticles with different dyes attached to their surface. The study was carried using a TD-DFTB model to describe the quantum dynamics of charge transfer in the presence of an external time dependent electric field simulating resonant illumination. The ZnO + dye systems have been classified according to the injection process (type I and type II) that they present. In addition, the calculated charge transfer shows that many dyes present hole injection into the nanoparticle. We have classified the charge transfer into holes or electron and compare these results with the TiO2 + dye system obtained from the literature.

Holographic equilibration under external dynamical electric field

The holographic equilibration of a far-from-equilibrium strongly coupled gauge theory is investigated. In particular, the dynamics of a probe D7-brane in an AdS-Vaidya background is studied in the presence of an external time-dependent electric field. Defining the equilibration times teqc and teqj, at which condensation and current relax to their final equilibrated values, receptively, the smallness of transition time kM or kE is enough to observe a universal behaviour for re-scaled equilibration times kMkE(teqc)−2 and kMkE(teqj)−2. kM(kE) is the time interval in which the temperature (electric field) increases from zero to finite value. Moreover, regardless of the values for kM and kE, teqc/teqj also behaves universally for large enough value of the ratio of the final electric field to final temperature. Then a simple discussion of the static case reveals that teqc≤teqj. For an out-of-equilibrium process, our numerical results show that, apart from the cases for which kE is small, the static time-ordering, that is teqc≤teqj, persists.

Communication: Influence of external static and alternating electric fields on water from long-time non-equilibrium ab initio molecular dynamics

The response of water to externally applied electric fields is of central relevance in the modern world, where many extraneous electric fields are ubiquitous. Historically, the application of external fields in non-equilibrium molecular dynamics has been restricted, by and large, to relatively inexpensive, more or less sophisticated, empirical models. Here, we report long-time non-equilibrium ab initio molecular dynamics in both static and oscillating (time-dependent) external electric fields, therefore opening up a new vista in rigorous studies of electric-field effects on dynamical systems with the full arsenal of electronic-structure methods. In so doing, we apply this to liquid water with state-of-the-art non-local treatment of dispersion, and we compute a range of field effects on structural and dynamical properties, such as diffusivities and hydrogen-bond kinetics.

Vacuum radiation induced by time dependent electric field

Many predictions of new phenomena given by strong field quantum electrodynamics (SFQED) will be tested on next generation multi-petawatt laser facilities in the near future. These new phenomena are basis to understand physics in extremely strong electromagnetic fields therefore have attracted wide research interest. Here we discuss a new SFQED phenomenon that is named as vacuum radiation. In vacuum radiation, a virtual electron loop obtain energy from time dependent external electric field and radiate an entangled photon pair. Features of vacuum radiation in a locally time dependent electric field including spectrum, characteristic temperature, production rate and power are given.

Dielectric function for free electron gas: comparison between Drude and Lindhard models

The interaction between light and metals or heavily doped semiconductors is largely determined by their free conduction electrons. The frequency and wave vector dependent complex dielectric function is an essential ingredient of the description of its optical and transport properties. The aim of this paper is to give a didactic introduction how the conduction electrons in solids responds to an external time dependent electric field and to make a comparison between Drude and Lindhard dielectric function models for the electron gas. In within framework of Lindhard model we derived an expression for dielectric function that is similar to the familiar Drudes's formula. In particular, the differences and similarities between the complex conductivity obtained from the two models are analyzed.

Pulsatile electroosmotic flow in a microcapillary with the slip boundary condition

The pulsatile electroosmotic flow (PEOF) of a Newtonian fluid in a circular microchannel with slippage at the surface is theoretically analyzed. It is assumed that the electroosmotic flow is started from rest by the sudden imposition of a time-dependent external electric field. The PEOF is controlled by the following dimensionless parameters: the normalized slip length, δ, defined as the ratio of the Navier length to the microcapillary radius; the angular Reynolds number, Rω, which quantifies the competition between the time scale for the diffusion of momentum across the microcapillary and the externally imposed time scale due to the oscillatory electric field; the parameter ɛ, which characterizes the amplitude of the oscillating electric field; the electrokinetic parameter κ¯, defined as the ratio of the characteristic length scale to the Debye length; and the ionic energy parameter, α, which compares the electric potential at the surface to the thermal potential. The analysis is conducted for low and high zeta potentials; in the former case, an analytical solution is obtained, whereas in the latter, a numerical solution is found. The results reveal that the volumetric flow rate is notably increased in a microchannel with slippage at the wall surface.

Electron Correlations in Local Effective Potential Theory

Local effective potential theory, both stationary-state and time-dependent, constitutes the mapping from a system of electrons in an external field to one of the noninteracting fermions possessing the same basic variable such as the density, thereby enabling the determination of the energy and other properties of the electronic system. This paper is a description via Quantal Density Functional Theory (QDFT) of the electron correlations that must be accounted for in such a mapping. It is proved through QDFT that independent of the form of external field, (a) it is possible to map to a model system possessing all the basic variables; and that (b) with the requirement that the model fermions are subject to the same external fields, the only correlations that must be considered are those due to the Pauli exclusion principle, Coulomb repulsion, and Correlation–Kinetic effects. The cases of both a static and time-dependent electromagnetic field, for which the basic variables are the density and physical current density, are considered. The examples of solely an external electrostatic or time-dependent electric field constitute special cases. An efficacious unification in terms of electron correlations, independent of the type of external field, is thereby achieved. The mapping is explicated for the example of a quantum dot in a magnetostatic field, and for a quantum dot in a magnetostatic and time-dependent electric field.