Nonlinear resonant transport of Bose-Einstein condensates

The coherent flow of a Bose-Einstein condensate through a quantum dot in a magnetic waveguide is studied. By the numerical integration of the time-dependent Gross-Pitaevskii equation in the presence of a source term, we simulate the propagation process of the condensate through a double barrier potential in the waveguide. We find that resonant transport is suppressed in interaction-induced regimes of bistability, where multiple scattering states exist at the same chemical potential and the same incident current. We demonstrate, however, that a temporal control of the external potential can be used to circumvent this limitation and to obtain enhanced transmission near the resonance on experimentally realistic time scales.     

局域共振型声子晶体中的缺陷态研究

本文以二维固体局域共振声子晶体为例,对次波长区域缺陷态的实现机理及其特点进行了探讨.众所周知,工作于次波长区域的声子晶体可以用有效媒质理论来描述,其色散关系对其构成单元的排列结构并不敏感,因而使得共振型声子晶体的带结构难以被其构成单元的局域空间无序所打破.本文发现共振型声子晶体在其带隙附近的色散关系可由共振单元间的长程相互作用来理解.基于这一理解,对目前文献中提出的两种实现局域态的方法进行了研究,结果表明缺陷态的引入正是通过打破这种长程相互作用来实现的.另外,在此理解的基础上,通过引入非各向同性"缺陷"共振单元,实现了纵波与横波导波模式的分离.     

Nonlinear spectroscopy of resonant levels by the photon-echo technique

A new method to measure the relaxation times of population, orientation and alignment of the resonant level is proposed.     

Nonlinear resonant light scattering by a polyatomic system

Polyatomic systems of two types are considered: a one-dimensional periodic chain of noninteracting dipoles and a plane layer of uniformly and irregularly distributed noninteracting dipoles. It is demonstrated that the Mollow triplet is observed in the spectrum of scattered radiation when the angles of strong field incidence are not very close to π/2. For sliding angles of strong field incidence on the system of dipoles, waves with frequencies of the strong field and high-frequency triplet component are scattered in forward and backward directions. In this case, radiation of low-frequency triplet component propagates along the layer on its bothsides in the form of two nonuniform waves attenuating exponentially with the distance from the layer.     

Ground state of a mixture of resonant condensates

It is shown that a two-component mixture of resonant condensates can be unstable toward the transition to the state with spontaneous Josephson oscillations in the absolute minimum of thermodynamic potential. The transition occurs stepwise at a certain critical value of the total number of particles or chemical potential.     

Nonlinear resonant two-wave interaction in an inhomogeneous medium

A one-dimensional steady-state nonlinear resonant two-wave interaction in a lossless periodically inhomogeneous medium is investigated. It is shown that the amplitudes and the phases of the waves vary in a stochastic manner.     

Nonlinear mode coupling in doubly resonant frequency doublers

The concept of a doubly resonant frequency doubler can be used for a variety of experiments concerning both classical phenomena like efficient frequency doubling at low power levels and quantum effects like squeezed states of light or Quantum Non Demolition (QND) measurements. In many of these experiments the strength of the nonlinear coupling of fundamental and second-harmonic modes is of crucial importance. First we treat the general theory for the calculation of the coupling parameter, which depends not only on properties of the nonlinear material but also on resonator geometry and some optical phases. On this basis we discuss in detail the situation for two different monolithic resonator geometries, namely a linear (standing-wave) and a ring (travelling-wave) cavity. Finally we compare theoretical predictions for these resonators to the experimentally achieved results.     

Nonlinear theory of resonant beam-plasma interaction: Nonrelativistic case

Analytic and numerical methods are used to study the nonlinear dynamics of the resonant interaction between a dense nonrelativistic electron beam and a plasma in a spatially bounded system. Regimes such as collective (Raman) and single-particle (Thomson) Cherenkov effects are considered. It is shown that in the first case, the motion of both the beam and plasma electrons exhibits significant nonlinearities. However, because of the weak coupling between the beam and the plasma, the nonlinear dynamics of the instability can be studied analytically and it can be strictly shown that saturation of instability is caused by a nonlinear shift of the radiation frequency and loss of resonance. In the second case, the nonlinear instability dynamics can only be studied numerically. In this regime, at low beam densities significant nonlinearity is only observed in the motion of the beam electrons while the plasma remains linear and saturation of the instability is caused by trapping of beam electrons in the field of the beam-excited plasma wave.     

Nonlinear dynamics study of an open resonant A-type system

A way resulting in lasing without inversion (LWI) in an open resonant A-type system from a nonlinear dynamics viewpoint is investigated. The destabilization of the non-lasing solution can occur not only through pitchfork bifurcation, giving rise to continuous wave LWI, but also through Hopf bifurcation,giving rise to self-pulsing LWI. This is much different from that of the corresponding closed resonant A-type system in which the destabilization of the non-lasing solution can occur only through pitchfork bifurcation. The effects of the unsaturated gain coefficient, cavity loss coefficient, atomic injection and exit rates on the two bifurcations are discussed.     

First resonant tunneling via a light-hole ground state

We report the demonstration of resonant tunneling of light-holes through an AlAs/GaAs P double-barrier heterostructure. The tensile strain in the quantum well reverses the order of the light- and heavy-hole levels, the first light-hole level becoming the ground state. The characteristics are measured at different temperatures and compared to those of a standard AlAs/GaAs unstrained structure. The peak current density of the first light-hole resonance and its peak-to-valley current ratio are enhanced. They reach 28 A/cm and 3.4 : 1 at 15 K. A negative differential resistance is observed up to 250 K.     

Lifetime of resonant state in a spherical quantum dot

This paper calculates the lifetime of resonant state and transmission probability of a single electron tunnelling in a spherical quantum dot (SQD) structure by using the transfer matrix technique. In the SQD, the electron is confined both transversally and longitudinally, the motion in the transverse and longitudinal directions is separated by using the adiabatic approximation theory. Meanwhile, the energy levels of the former are considered as the effective confining potential. The numerical calculations are carried out for the SQD consisting of GaAs/InAs material. The obtained results show that the bigger radius of the quantum dot not only leads significantly to the shifts of resonant peaks toward the low-energy region, but also causes the lengthening of the lifetime of resonant state. The lifetime of resonant state can be calculated from the uncertainty principle between the energy half width and lifetime.     

Nonlinear dynamics of high-density electron-beam resonant instabilities. Analytical solution

We obtain an analytical solution of the nonlinear dynamics of a resonant instability in a dense electron beam. It is shown that the instability of a dense beam saturates because of a nonlinear frequency shift and a deviation from the resonance condition.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 31–35, January, 1984.The authors acknowledge useful discussions with A. A. Rukhadze.     

Nonlinear resonant polarization rotation under conditions of coherent population trapping

Nonlinear resonant optical rotation was studied over a wide range of experimental parameters at the Rb D ₁ F = 2→F′ = 1 transition in the ⁸⁷Rb vapor under conditions of coherent population trapping. The angle of rotation was found to depend nonmonotonically on the laser intensity and applied magnetic field. The effect of optical pumping out to the level F = 1 is discussed. It is demonstrated experimentally that the Faraday rotation angle increases twofold upon the compensation for pumping.     

Nonlinear galloping of internally resonant iced transmission lines considering eccentricity

Based on the curved-beam theory, a nonlinear galloping model considering three displacement (normal, bi-normal and tangential) components and twist is formulated. According to the property of transmission line, one reduced (normal and bi-normal) galloping model, with regard of bending, rotation and eccentricity of cross section, is obtained. Moreover, the initial rotation angle is also introduced in galloping and aerodynamic models. Additionally, based on the reduced model, the bifurcation and stability of the two cases (1:1 resonance and 2:1 resonance) are analyzed. The results turn out that the importance of ice eccentricity needs to be highlighted. Finally, multiple stabilities are found through the analyses of bifurcation and stability and proved by the reduced model and Reduced Amplitude Modulation Equations (RAME) numerically integrated in time history.     

Particle decay of resonant state generated by direct reaction

A framework is presented for studying two step reactions illustrated byA+a→B ^*+b, B^*→C+c. In the first step, a direct reaction excites a resonant state (e.g., giant resonances or isobaric analog resonances), which decays by a particle emission in the second step. Feshbach's projection operator method is used to obtain a reaction amplitude, which consists of a compound part and a direct part. The latter corresponds to a knock-out process when the direct reaction is inelastic scattering. A compound part includes contributions from the direct decay of doorway states as well as the multistep decay. The statistical theory of precompound reactions is applied to this multistep decay and an explicit expression is given for the cross section.     

Observation of resonant behavior in the energy velocity of diffused light

In this Letter we demonstrate Mie resonances mediated transport of light in randomly arranged, monodisperse dielectric spheres packed at high filling fractions. By means of both static and dynamic optical experiments we show resonant behavior in the key transport parameters and, in particular, we find that the energy transport velocity, which is lower than the group velocity, also displays a resonant behavior.     

Nonlinear optics and the defect solid state

Abstract

The condition for the generation of second harmonics in the dipole approximation is that the nonlinear crystal medium lack a center of inversion. Conversely, a center of inversion precludes optical second harmonic generation. It is well known, however, that lattice defects introduced into a crystal may alter the local point symmetry in the medium, and in fact may convert local inversion symmetry to that which corresponds to a noncentrosymmetric point group. It is thus clear that selected defects in nonlinear media may be of interest for studying nonlinear optical processes which depend on the square of the electric field strength. The specific case of second harmonic generation employing spatially ordered FA-centers in alkali halide crystals is considered.