Time-dependent Laser Field Research Articles

Imprints of multielectron polarization effects in odd-even harmonic generation from CO molecules

Dynamic core-electron polarization (DCeP) is a correction to the single-active electron (SAE) approximation by considering a response of the core electrons to the time-dependent laser field. Despite being initially construed as a perturbative correction, in some cases especially atoms and molecules with large polarizabilities, DCeP can qualitatively alter predictions produced by the bare SAE theory. In this study, we unambiguously demonstrate the nonperturbative role of DCeP in the resolved odd-even high-order harmonic generation (HHG) of the CO molecule. In particular, we find that the even-to-odd ratio, i.e., the ratio between the harmonic intensities of even order and average of the two adjacent odd orders, changes by as much as one order of magnitude when DCeP is included, making the theoretically predicted values remarkably consistent with the experimental ones. This strong manifestation allows us to verify the DCeP role in HHG by experimental data. Furthermore, our analysis of the harmonic time profile shows that this agreement is not an artifact of the numerical method but reflects relevant physics, establishing that DCeP must be incorporated into the standard framework for strong-field physics.

Dissipative preparation of qutrit entanglement via periodically modulated Rydberg double antiblockade.

We propose a mechanism of Rydberg double antiblockade by virtue of a resonant dipole-dipole interaction between a pair of Rydberg atoms placed at short distances scaling as 1/R3. By combining this novel excitation regime with microwave-driven fields and dissipative dynamics, a stationary qutrit entangled state can be obtained with high quality, the corresponding steady-state fidelity and purity are insensitive to the variations of the dynamical parameters. Furthermore, we introduce time-dependent laser fields with periodically modulated amplitude to speed up the entanglement creation process. Numerical simulations reveal that the order of magnitude of the shortened convergence time is about 103 in units of ω0, and the acceleration effect appears valid in broad parametric space. The present results enrich the physics of the Rydberg antiblockade regimes and may receive more attention for the experimental investigations in dissipative dynamics of neutral atoms.

Direct sampling of a light wave in air

Temporal characterization of a laser pulse is an essential task in many applications. Temporal characterization methods that are currently available support only a limited spectral bandwidth without information on the carrier-envelope phase (CEP) of the laser pulse or require complicated equipment in a vacuum environment. Here we demonstrate that an arbitrary time-dependent laser field can be directly sampled using subcycle tunneling ionization in a gaseous medium or in air. The subcycle ionization is used as a fast temporal gate for the direct sampling of the laser field. This unique approach enables the complete temporal characterization of the laser field, including its CEP, for a broad spectral range in ambient air, providing a universal tool for the precise measurement of the laser field.

Run-and-tumble-like motion of active colloids in viscoelastic media

Run-and-tumble motion is a prominent locomotion strategy employed by many living microorganisms. It is characterized by straight swimming intervals (runs), which are interrupted by sudden reorientation events (tumbles). In contrast, directional changes of synthetic microswimmers (active particles) are caused by rotational diffusion, which is superimposed with their translational motion and thus leads to rather continuous and slow particle reorientations. Here we demonstrate that active particles can also perform a swimming motion where translational and orientational changes are disentangled, similar to run-and-tumble. In our system, such motion is realized by a viscoelastic solvent and a periodic modulation of the self-propulsion velocity. Experimentally, this is achieved using light-activated Janus colloids, which are illuminated by a time-dependent laser field. We observe a strong enhancement of the effective translational and rotational motion when the modulation time is comparable to the relaxation time of the viscoelastic fluid. Our findings are explained by the relaxation of the elastic stress, which builds up during the self-propulsion, and is suddenly released when the activity is turned off. In addition to a better understanding of active motion in viscoelastic surroundings, our results may suggest novel steering strategies for synthetic microswimmers in complex environments.

A tunable mechanism to control photo-dissociation with invariant tori with variable energies

In this work, we investigate the classical dynamics of a polar diatomic molecule under the action of a space and time-dependent laser field. In the absence of laser fields, the phase space consists of a bound and an unbound region divided by a separatrix. When an interacting laser field is present, some surviving invariant tori are deformed. Therefore, the initial conditions in the bound region which are over the surviving tori may visit the unbound region but still undergoing a bounded motion. Based on this analysis, we propose a mechanism to control the photo-dissociation process using the driven Morse oscillator as a model.

More New Exact Solutions for Bose Einstein Condensate in Weak Bias Magnetic and Time Dependent Laser Field

With the aid of Mathematica software, in this paper, based on Wu computation algorithms, we offer a direct and systematic extended function transform method of solving general variable coefficient nonlinear partial differential equation or equations. By applying this effectiveness method, more new exact solutions are successfully obtained for variable coefficient nonlinear schrǒdinger equation which described Bose Einstein Condensate in weak bias magnetic and time-dependent laser field.

Applications of Basis Light-Front Quantization to QED

Hamiltonian light-front quantum field theory provides a framework for calculating both static and dynamic properties of strongly interacting relativistic systems. Invariant masses, correlated parton amplitudes and time-dependent scattering amplitudes, possibly with strong external time-dependent fields, represent a few of the important applications. By choosing the light-front gauge and adopting an orthonormal basis function representation, we obtain a large, sparse, Hamiltonian matrix eigenvalue problem for mass eigenstates that we solve by adapting ab initio no-core methods of nuclear many-body theory. In the continuum limit, the infinite matrix limit, we recover full covariance. Guided by the symmetries of light-front quantized theory, we adopt a two-dimensional harmonic oscillator basis for transverse modes that corresponds with eigensolutions of the soft-wall anti-de Sitter/quantum chromodynamics (AdS/QCD) model obtained from light-front holography. We outline our approach and present results for non-linear Compton scattering, evaluated non-perturbatively, where a strong and time-dependent laser field accelerates the electron and produces states of higher invariant mass i.e. final states with photon emission.

Model for atomic dielectric response in strong, time-dependent laser fields

A nonlocal quantum-mechanical model is presented for calculating the atomic dielectric response to a strong laser electric field. By replacing the Coulomb potential with a nonlocal potential in the Schr\"odinger equation, a 3 + 1-dimensional calculation of the time-dependent electric dipole moment can be reformulated as a 0 + 1-dimensional integral equation that retains the three-dimensional dynamics, while offering significant computational savings. The model is benchmarked against an established ionization model and ab initio simulation of the time-dependent Schr\"odinger equation. The reduced computational overhead makes the model a promising candidate to incorporate full quantum-mechanical time dynamics in laser pulse propagation simulations.

Electron dynamics of interatomic Coulombic decay in quantum dots induced by a laser field

In this paper we investigated the dynamics of an electron in the presence of a time-dependent laser field in a model potential for a two-level single-electron semiconductor quantum dot (QD) that is capable of undergoing interatomic Coulombic decay (ICD) together with an electron bound to a neighboring QD. We demonstrate that ICD can be initiated by coupling the two-level QD to either a continuous or a pulsed moderate to strong laser and we obtain the total and partial decay widths of the resonance excited state in agreement with that from the solely decay of the resonance [A. Bande, K. Gokhberg, and L. S. Cederbaum, J. Chem. Phys. 135, 144112 (2011)]. A detailed discussion of the effects of direct ionization by the laser in single- or multi-photon process as well as Rabi oscillations is furthermore presented.

Dynamics of Particle in Confined-Harmonic Potential in External Static Electric Field and Strong Laser Field

Dynamics of a particle in confined-harmonic potential, subjected to external static electric and time-dependent laser fields is studied. The energy levels and wave functions of unperturbed harmonic oscillator are evaluated using B-polynomial Galerkin method. Matrix formulation is used throughout the procedure. This procedure is very simple and efficient in comparison with other methods. Modifications of wave functions and energy levels due to static electric field are also calculated. Finally, absorption spectra of such a driven oscillator are studied and explained.

Quantum dot–metallic nanorod sensors via exciton–plasmon interaction

We investigate quantum nanosensors based on hybrid systems consisting of semiconductor quantum dots and metallic nanorods in the near-infrared regime. These sensors can detect biological and chemical substances based on their impact on the coherent exciton–plasmon coupling and molecular resonances supported by such systems when they interact with a laser field. We demonstrate that the ultrahigh sensitivity of such molecular resonances on environmental conditions allows dramatic and nearly instantaneous changes in the total field experienced by the semiconductor quantum dot via minuscule variations of the local refractive indices of the quantum dot or nanorod. The proposed nanosensors can utilize quantum effects to control the sense (or direction) of the changes in the quantum dot emission, allowing us to have bistable switching from dark to bright states or vice versa via adsorption (or detachment) of biomolecules. These sensors can also offer detection of ultra-small variations in the local dielectric constant of the quantum dots or metallic nanorods via coherent induction of time delays in the effective field experienced by the quantum dots when the hybrid systems interact with time-dependent laser fields. This leads to unprecedented bulk refractive index sensitivities. Our results show that one can utilize quantum phase to control the coherent exciton–plasmon dynamics in these sensors such that introduction of a biomolecule can increase or decrease the time delay. These results offer novel ways to detect single biomolecules via application of quantum coherence to convert their impact into spectacular optical events.

Matter-wave solutions of Bose—Einstein condensates with three-body interaction in linear magnetic and time-dependent laser fields

We construct, through a further extension of the tanh-function method, the matter-wave solutions of Bose—Einstein condensates (BECs) with a three-body interaction. The BECs are trapped in a potential comprising the linear magnetic and the time-dependent laser fields. The exact solutions obtained include soliton solutions, such as kink and antikink as well as bright, dark, multisolitonic modulated waves. We realize that the motion and the shape of the solitary wave can be manipulated by controlling the strengths of the fields.

Exact transient photon correlation with arbitrary laser pulses

We present a full quantum theory to study the transient evolution of photon pairs. We introduce a method which gives exact time-dependent solutions of the coupled quantum Langevin equations for a multilevel quantum particle driven by arbitrary time-dependent laser fields. The analytical solutions are used to develop a numerical code for computing exact time evolution of the two-photon correlation function. We analyze the effects of laser pulses sequence, pulse duration, chirping, and initial internal quantum states on the nonclassicality of the photon correlation through the violation of the Cauchy-Schwarz inequality. The results provide a promising possibility of controlling the generation of highly correlated photon pairs using tailored short laser pulses.

Exact Solutions of Bose-Einstein Condensate in Linear Magnetic Field and Time-Dependent Laser Field

Nonlinear evolution equations (NLEEs) are frequently used to model a wide variety of phenomena in physics, chemistry, biology and even in social science field. Seeking and constructing exact solutions especially soliton solutions of NLEEs is one of the most important and essential task in nonlinear science. With the help of exact solutions, when they exist, the nonlinear phenomena can be better understood. In the past decades, various sophisticated methods have been created such as the inverse scattering method [1], the Backlund transformations [2], the Darboux transformations [3] and the Hirota bilinear method [4]. Especially, in recent years, with the rapid development of computerized symbolic computation, many direct and effective algebraic methods are proposed such as the homogeneous balance method [5], tanh function method [6], the Jacobi elliptic function expansion method [7], the F-expansion techniques [8], exp-function method [9] and so on. Recently, Wang et al. [10] introduced a new direct method called G ′ G -expansion method for a reliable treatment of the NLEEs. Then this method is generalized and widely used to seek travelling wave solutions, non-travelling wave solutions and coefficient function solutions for many nonlinear physical models [11–14], and even extended to solve NLEE with variable coefficients [15]. The Gross–Pitaevskii equation appears as a relevant model in various areas of physics: nonlinear optics, fluid mechanics, Bose–Einstein condensation (BEC). The realization of BEC of weakly interacting atomic gases stim-

Envelope Periodic Solutions to Bose–Einstein Condensation in Linear Magnetic Field and Time-Dependent Laser Field

In this paper, by applying the extended Jacobi elliptic function expansion method, the envelope periodic solutions and corresponding dark soliton solution, bright soliton solution to Bose–Einstein condensation in linear magnetic field and time-dependent laser field are obtained.

Piecewise static Hamiltonian for an atom in a strong laser field

We show that it is possible to use a piecewise constant Hamiltonian to describe the main features of the dynamics of an atom interacting with a laser field. In particular we show that using this approximation we are able to give a good description of the ionization signal, of the HHG spectra and of the attosecond pulses generated by the radiating electron. Finally, we give an explicit formula to evaluate the ionization rate in the time dependent laser field. This formula, which is a generalization of the Landau formula for the ionization rate of an atom in a static electric field, fairly well reproduces the numerical ionization rates for a broad range of laser frequency and intensity. The main advantage of this formula is that it can be used well beyond the limits of the quasi-static formula for the ionization rate of an atom.

Entanglement sudden birth of two trapped ions interacting with a time-dependent laser field

We describe some new features of quantum entanglement in two three-level trapped ions confined in a one-dimensional harmonic potential, allowing the instantaneous position of the centre-of-mass motion of the ions to be explicitly time dependent. By solving the exact dynamics of the system, we show how survivability of the quantum entanglement is determined by a specific choice of the initial state settings. In particular, we discuss the underlying conditions that may lead to the phenomena of entanglement sudden birth (delayed creation of entanglement) and sudden death (non-smooth finite-time decay).

Tailoring current flow patterns through molecular wires using shaped optical pulses

Combining the features of molecular wires and femtosecond laser pulses gives the unique opportunity to optically switch electron currents in molecular devices with very high speed. Based on a weak-coupling approximation between wire and leads, a quantum master equation for the population dynamics and the electric current through the molecular wire has been developed, which allows for arbitrary time-dependent laser fields interacting with the wire. This formalism is combined with the theory of optimal control, leading to an innovative control of targets distributed in time in open quantum systems. For a tight-binding approximation of the molecular wire, we show how to compute the laser pulses to switch the current through the wire on and off. With this approach, the current flow pattern of the current in time can be chosen in an almost arbitrary fashion.

Dynamical and Geometric Phases of a Two Energy-LevelBose–Einstein Condensate Interacting with a Laser Field

By using of the invariant theory, we study a two energy-levelBose–Einstein condensate interacting with a time-dependent laser field,the dynamical and geometric phases are given respectively. TheAharonov–Anandan phase is also obtained under the cyclical evolution.

Phase of Bose-Einstein Condensate Interacting with a Time-Dependent Laser Field

By using of the invariant theory, we have studied phase of Bose-Einstein condensate in a double-well potential interacting with a time-dependent single-mode traveling-wave laser field, the dynamical and geometric phases are presented respectively. The Aharonov-Anandan phase is also obtained under the cyclical evolution.