Horizontal rolls in convective flow above a partially heated surface

Considering the nonlinearity arising from the interaction between electrons and lattice vibrations, an effective electronic model with a self-interaction cubic term is employed to study the interplay between electron-electron and electron-phonon interactions. Based on numerical solutions of the time-dependent nonlinear Schroedinger equation for an initially localized two-electron singlet state, we show that the magnitude of the electron-phonon coupling χ necessary to promote the self-trapping of the electronic wave packet decreases as a function of the electron-electron interaction U. We show that such dependence is directly linked to the narrowing of the band of bounded two-electron states as U increases. We obtain the transition line in the χ × U parameter space separating the phases of self-trapped and delocalized electronic wave packets. The present results indicates that nonlinear contributions plays a relevant role in the electronic wave packet dynamics, particularly in the regime of strongly correlated electrons.     

Diffraction of the wave packet of a three-level Λ atom in the field of a multifrequency standing light wave

The diffraction of the wave packet of a three-level atom in a multifrequency optical radiation field is studied. A new type of coherent beam splitter for atoms that employs the scattering of a wave packet in the field of four standing light waves with different spatial shifts is proposed on this basis. It is shown that this interaction scheme makes it possible to obtain large splittings (>100ℏk) of the wave packet of a three-level Λ atom in momentum space into only two coherent components. In addition, the atoms in these coherent components are in long-lived atomic states, which substantially simplifies the experimental implementation of such a splitter. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 386–391 (25 September 1997)     

Isotope-selective femtosecond wave packet dynamics: The rare molecule

For the first time, the femtosecond real-time vibrational dynamics of the rare ^41,41K₂ isotope, excited to the electronic state, could be selectively studied by means of time-resolved three photon ionization. A vibrational period of fs is determined. Superimposed, a beat structure with a period of 20 ps is observed. A detailed Fourier analysis reveals a strong band of three lines centered around 65.5 cm^-1. A significant perturbation of the wave packet caused by spin-orbit coupling of the A and the crossing state is found. This perturbation is the reason for the fast dephasing of the initially generated wave packet within about 10 ps. The spectrogram of the real-time data shows total revivals of the wave packet at 20 ps and 40 ps. Fractional revivals are found for times around 10 ps and 30 ps. Due to high intensity effects a remarkable slightly broadened line at 90 cm^-1 appears and can be assigned to the wave packet propagation generated in the dimer's ground state by impulsive stimulated Raman scattering. Revivals of this ground state wave packet are found at 17ps and 34ps. A comparison with other isotopes of K₂ is given. Received: 9 February 1998 / Revised: 15 May 1998 / Accepted: 2 June 1998     

Bragg reflection during the propagation of magnetoelastic microwave pulses in a structure consisting of a ferrite thin film on a dielectric substrate

The propagation of a microwave pulse in a ferrite thin film-substrate structure in a regime of rereflections (“ringing”) of the acoustic component of the substrate is studied theoretically. It is shown that as a result of the interaction of microwave pulses with the boundaries of the substrate, propagation of a microwave excitation in this system can be regarded as a propagation of a wave packet in a periodic nonuniform medium. The basic characteristics of a propagating wave packet are obtained. Zh. Tekh. Fiz. 69, 82–86 (December 1999)     

Motion of an electronic wave packet in an electromagnetic field

An equation is derived for the matrix of the parameters of a small Gaussian wave packet moving in arbitrary fixed electromagnetic fields. The equation can be used to describe the evolution of wave packets in a wide class of vacuum devices. A simple example of the evolution of a packet in a constant magnetic field is studied. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 515–520 (25 October 1996)     

Experimental scheme for quantum teleportation of a one-photon packet

A complete protocol and an optical scheme for experimental implementation of the quantum teleportation of an unknown one-photon wave packet are proposed. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 248–254 (10 August 1998)     

Evolution of the width of the wave packet of a charged particle interacting with a quantum electromagnetic field

The path integral method is used to study the width of the wave packet of a relativistic charged particle interacting with a quantum electromagnetic field. A general expression is derived for the density distribution of a particle moving in arbitrary external potentials. An electron synchrotron with weak focusing is studied as a specific example, and the width of the wave packet of an electron moving in this accelerator is found. Zh. éksp. Teor. Fiz. 111, 1563–1578 (May 1997)     

Transmission times of wave packets tunneling through barriers

The transmission of wave packets through barriers by tunneling is studied in detail by the method of quantum molecular dynamics. The distribution of the arrival times of a tunneling packet in front of and behind a barrier and the momentum distribution function of the packet are calculated. The average position and average momentum of the packet and their spread are investigated. It is found that below the barrier a part of the packet is reflected, and a Gaussian barrier increases the average momentum of the transmitted packet and its spread in momentum space. Zh. éksp. Teor. Fiz. 115, 1872–1889 (May 1999)     

Misinterpretation yields supervelocities during transmission of wave packets through a barrier

This paper is concerned with the transmission time of an incident Gaussian wave packet through a symmetric rectangular barrier. Following Hartman (J. Appl. Phys. 33, 3427 (1962)), the transmission time is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission velocity which appears under certain conditions as a supervelocity, i.e. becomes larger than the corresponding propagation velocity in free space which is the group velocity for electrons or the velocity of light for photons, respectively. By analysing the propagation of a broadband wave packet (which leads in free space to an extremely concentrated wave packet at a certain time) we obtain the pulse response function of the barrier and show that the insertion of the barrier is physically unable to produce a supervelocity. Therefore, the peak of an incident Gaussian wave packet and the peak of the transmitted wave packet are in no causal relationship. The shape of the transmitted wave packet is produced from the incident wave by convolution with the pulse response of the barrier. This yields a distortion of the shape of the wave packet which includes also the observed negative time shift of the peak. We demonstrate further that the phenomenon of Hartman's supervelocities is not restricted to barriers with their exponentially decaying fields but occurs for instance also in transmission lines with an inserted LCR circuit. Received 7 January 1999 and Received in final form 22 April 1999     

Generation of one-photon states by a quantum dot

A technique for preparation of a one-photon wave packet through action of a classical electromagnetic field on a semiconducting quantum dot is proposed. We demonstrate that the Coulomb repulsion between charge carriers allows one to select the frequency, amplitude, and duration of an electromagnetic pulse so that one electron will transfer from an upper size-quantized level of the valence band to a lower size-quantized level of the conduction band with a probability close to unity. As a result of radiative recombination of the produced electron-hole pair, exactly one photon is emitted (a one-photon wave packet). This source of one-photon states can be used in quantum systems of data transmission and in quantum computers. Zh. éksp. Teor. Fiz. 112, 1257–1272 (October 1997)     

Electronic spectrum of a two-dimensional Fibonacci lattice

The electronic spectrum and wave functions of a new quasicrystal structure—a two-dimensional Fibonacci lattice—are investigated in the tight-binding approximation using the method of the level statistics. This is a self-similar structure consisting of three elementary structural units. The “central” and “nodal” decoration of this structure are examined. It is shown that the electronic energy spectrum of a two-dimensional Fibonacci lattice contains a singular part, but in contrast to a one-dimensional Fibonacci lattice the spectrum does not contain a hierarchical gap structure. The measure of allowed states (Lebesgue measure) of the spectrum is different from zero, and for “central” decoration it is close to 1. The character of the localization of the wave functions is investigated, and it is found that the wave functions are “critical.” Zh. éksp. Teor. Fiz. 116, 1834–1842 (November 1999)     

Low-frequency plasmons in coupled electronic microstructures

The plasmon spectrum and the absorption of an electromagnetic wave in an electronic two-dimensional plasma with strongly modulated density are studied. The appearance of additional plasmon modes in a system of electronic wires and islands with weak current coupling is described in a model of an electronic system covered with metallic gates. Such plasmon modes appear in the low-frequency region of the spectrum, as compared with the conventional plasma oscillations, and have recently been observed experimentally in paired wires. Fiz. Tverd. Tela (St. Petersburg) 40, 542–545 (March 1998)     

Pump-probe photoionization study of the passage and bifurcation of a quantum wave packet across an avoided crossing

The application of femtosecond pump-probe photoelectron spectroscopy to directly observe vibrational wave packets passing through an avoided crossing is investigated using quantum wave packet dynamics calculations. Transfer of the vibrational wave packet between diabatic electronic surfaces, bifurcation of the wave packet, and wave packet construction via nonadiabatic mixing are shown to be observable as time-dependent splittings of peaks in the photoelectron spectra.     

Generation of squeezed states on reflection of light from a system of free electrons

The statistical characteristics of an electromagnetic wave reflected from a system of successive free-electron mirrors are investigated. Such a configuration of the electron stream is characteristic in particular for free-electron lasers. An expresson is obtained for the squeeze factor of the field of the reflected wave, and the optimal geometric configuration of the system of electrons is found. Numerical estimates show that the squeezing can be substantial when the number of electronic mirrors is large. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 160–165 (10 February 1996)     

Calculation of thermal effects in the photodesorption of NO from NiO(100)

The influence of temperature in the photodesorption of NO from a NiO(100)-surface is studied with a two-dimensional quantum wave packet approach. The complete process including laser-induced excitation and subsequent relaxation is treated explicitly from first principles. The electronic quenching caused by the interaction of the excited adsorbate–substrate system with electron–hole-pairs in the surface is treated with the surrogate Hamiltonian approach. We have implemented a parallelization scheme of the wave packet propagation based on a one-dimensional data decomposition to perform simulations in a reasonable computing time. The results are compared with mixed quantum-classical simulations and with experimental measurements. Both desorption yield and mean velocity of the desorbing molecules were enhanced with increasing temperature. The calculated rotational temperatures are consistent with experimental results. PACS  79.20.La; 68.43.Tj     

Theoretical Study of the Influence of Femtosecond Laser Wavelength on the Evolution of a Double-Minimum Electronic Excited State Wave Packet for NaRb

Employing the two-state model and the time-dependent wave packet method, the influence of femtosecond laser wavelength on the evolution of the double-minimum electronic excited state wave packet is numerically investigated. For different laser wavelengths, evolutions of the double-minimum electronic excited state wave packet with time and internuclear distance are different. One can control the evolution of the wave packet by varying the laser wavelength appropriately, which will benefit the light manipulation of atomic and molecular processes. Furthermore, study of the dynamics of the NaRb molecule may yield clues to creating an ultracold molecule.     

Thermal conductivity of nonlinear waves in disordered chains

We present computational data on the thermal conductivity of nonlinear waves in disordered chains. Disorder induces Anderson localization for linear waves and results in a vanishing conductivity. Cubic nonlinearity restores normal conductivity, but with a strongly temperature-dependent conductivity κ(T). We find indications for an asymptotic low-temperature κ ∼ T ⁴ and intermediate temperature κ ∼ T ² laws. These findings are in accord with theoretical studies of wave packet spreading, where a regime of strong chaos is found to be intermediate, followed by an asymptotic regime of weak chaos (Laptyeva et al, Europhys. Lett. 91, 30001 (2010)).     

Integrable chain of electrons interacting with phonons

The exact wave function of a chain of electrons interacting with local phonons is constructed. The ground-state energy and the gap in the electronic excitation spectrum are calculated. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 83–88 (25 January 1996)     

Two-level electron dynamics in a strong variable external field

This paper studies the quantum dynamics of an electron in a double-well potential subject to a strong time-periodic nonharmonic external field. The quasienergy spectrum of the system is calculated and an expression for the electron density distribution is derived. It is found that under certain conditions imposed on the shape of the excitation, the electron wave packet gets locked, into one potential well, as it were, and is unable to tunnel through the potential barrier. Zh. éksp. Teor. Fiz. 112, 1209–1225 (October 1997)     

一般幂指数中心势作用下的波包回归和部分回归

利用WKB近似和自关联函数方法,我们研究了一般幂指数中心势V(r)=γrk (-20)作用下波包的回归和部分回归.对于排斥势(γ>0, k>0), 势是一长程势,量子化能级结构中只有一个量子数,波包的回归结构和一维幂指数势的情况类似.这一结果表明能级结构相同的体系具有相同的波包回归结构.对于吸引势,能级结构中有两个量子数, 当 k取不同的值时,波包的回归结构不同.对于库仑吸引势,波包回归和部分回归出现;但是对于其它的k值, 经过一段时间后,波包出现坍塌.本文的研究对于探讨里德堡原子和分子中电子运动的经典极限提供了一个新的方法.