Atomic Dipole Dynamics in the Thermal Quantized Cavity Field

Abstract

We consider the resonant interaction of a two-level atom with a thermal state of the quantized field in a lossless cavity. Non-trivial dynamics of the atomic dipole moment and the field quadrature components arise if the atom is initially prepared in a coherent superposition of its upper and lower states. In particular, the initial thermal field state acquires a well defined phase that corresponds to the initial phase of the superposition atomic state. Population trapping occurs when the intensity grows.     

Dynamics of a Flux Qubit Coupled with a Quantized Electromagnetic Mode of a Lossy Cavity

The dynamics of a rf-SQUID qubit placed within a 1-D lossy resonant cavity is reported. Initially preparing the combined system in a state with no more than one excitation, the effects of loss mechanisms can be carefully analyzed, for different values of the cavity quality factor Q. The results here discussed demonstrate the possibility of controlling these phenomena in such a way to be able to observe “coherent” Rabi oscillations and the periodically generation of factorized and entangled states (with a priori known characteristics). The importance of these results in the general context of quantum communications is carefully discussed as well as some technical detail necessary for the experimental feasibility of my theoretical scheme.     

Quantum Dynamics of a Hyper-Raman Coupled Model Interacting with Two Quantized Cavity Fields

The quantum dynamics of a hyper-Raman coupled model interacting with two modes of the quantized cavity field is described. The model consists of a four-level atom in a v configuration where transitions between the ground and excited states occur through the absorption (emission) of two photons from one mode and the emission (absorption) of one photon from the other and where two intermediate states are taken to be far off-resonance and are adiabatically removed. This is a multiphoton extension of the Jaynes-Cummings model and is exactly solvable. We study the atomic inversion and investigate the production of non-classical light exhibiting antibunching, violations of the Cauchy-Schwartz inequality, and squeezing.     

Coherent Dynamics of Localized Spins in an Inhomogeneous Magnetic Field

We studied the influence of the inhomogeneity of fringe fields originating from nanostructured ferromagnets on the coherent dynamics of localized Mn²⁺ spins in a (Zn,Cd,Mn)Se/ZnSe quantum well by time-resolved Kerr rotation. By studying hybrid systems with different geometry, we demonstrate that the spatially inhomogeneous fringe field results in two main consequences for the localized spin system: First, a temporal variation of the ensemble precession frequency is obtained, and second, a reduced ensemble spin dephasing time T ₂^* is observed in comparison to an unstructured reference area of the sample.     

Dynamics of Spinor Condensates Driven by an Inhomogeneous Magnetic Field

A variational wavefunction including the breather, dipole and scissor modes simultaneously is constructed to investigate the collective-excitation dynamics of spin-1 \(^{87}\mathrm{Rb}\) condensates driven by a space- and time-dependent magnetic field. When the Dirac point never enters the condensate, it is shown that the dipole, breather and scissor modes will be all excited driven by the sinusoidal oscillation of the Dirac point, due to the coupling of different collective modes from the inhomogeneity of the magnetic field. A resonance-driving phenomenon is observed. If the Dirac point passes through the condensate, our numerical results agree with most experimental observations (Ray et al. in Nature 505:657, 2014) and find that the center of mass of the condensate does not follow the zero point of the magnetic field. Hopefully, our method can be extended to study the similar dynamics for the other spinor condensates.     

Dynamics of Quantized Vortices in a Rotating Cylindrical Vessel

Recently Finne et al. found a transition to the turbulent state in rotating superfluid ³He-B which is insensitive to the fluid velocity, but rather controlled by temperature. They reported that at low temperatures a few seed vortices, injected into a vortex-free region, developed through a transient turbulent state to a vortex array. The experimental observations were consistent with the numerical simulation of dynamics of quantized vortices. However, we do not understand well how the seed vortex follows the above scenario and, especially, how the turbulent vortices change to a vortex array. Although the previous numerical simulation was done for a rotating cubic vessel, we study here the vortex dynamics in a rotating cylindrical vessel which is more suitable for the comparison with the experiments. We developed a numerical method for calculating the vortex dynamics in a cylindrical vessel and investigated the vortex dynamics after a vortex seed loop was injected into a vortex-free region. The numerical result shows that the seed vortex becomes unstable, especially near the cylindrical side wall, and develops into turbulent vortices. After that a vortex array appears in the central region, collecting the vortices from the surrounding tangle. PACS numbers: 67.40.Vs, 47.32.Cc, 47.37.+q.     

Dusty Plasma in a Strongly Inhomogeneous Magnetic Field

Technical Physics Letters - We report results of the first investigation of dusty plasma formed in glow discharge in the region of a strongly inhomogeneous magnetic field with a field gradient...     

Heat and Mass Flux Effects on a Moving Vertical Cylinder with Chemically Reactive Species Diffusion

This paper presents the development of the free convection boundary layer flow of a viscous and incompressible fluid past an impulsively started semi-infinite vertical cylinder with uniform heat and mass fluxes and chemically reactive species. The governing coupled nonlinear partial differential equations have been solved numerically using the finite-difference scheme of Crank–Nicolson type. Graphical results for the velocity, temperature, concentration, local and average skin friction, Nusselt number and Sherwood number profiles are illustrated and discussed for various physical parametric values. It is noted that due to the presence of first-order chemical reaction the velocity decreases with increasing values of the chemical reaction parameter     

Coherent Atomic Excitation in a Cavity. I. Low Density

Abstract

We present a procedure for treating coherent selective excitation (and subsequent ionization) of atomic vapour in a radiation-filled cavity. Specifically, we describe a technique for solving the coupled Maxwell-Bloch equations for atoms in a one-dimensional cavity by means of a spatial quasi-Fourier expansion that introduces a sequence of increasing spatial harmonics for atomic populations and coherences. We discuss the resulting coupled equations and present examples of solutions for a simple model of stationary and moving two-state atoms in the limit of very low density. The atomic excitation exhibits a travelling wave behaviour, but with significant modulation.     

Dynamics of Quantized Vortices in Bose-Einstein Condensates Trapped in Precessing Potential

We study numerically and analytically dynamics of Bose-Einstein condensates trapped in precessing potential. The precessing potential has two frequencies because the trapping potential rotates around one axis with one frequency, and this axis rotates around the other axis with the other frequency. In this paper, we treat a situation in which the second frequency is much smaller than the first. The vortex lattice formed by the first rotation rotates around the second axis, following the rotating axis. We find numerically an interesting steady state in which the vortex lattice lags by a finite angle behind the rotating axis. We discuss analytically the origin of this steady state.     

Finite-Element Simulation of Mass Transfer in Structurally Inhomogeneous Materials

The problem of nonisothermal hydrogen diffusion with variable coefficients of diffusion and solubility of hydrogen for structurally heterogeneous materials is solved by the finite-element method. The proposed algorithm is checked by finding the solution of the problem of hydrogen diffusion in a bimetallic structural element. It is shown that nonstationary thermal processes (variations of temperature) in materials may lead to the formation of zones of temporal overequilibrium supersaturation with hydrogen and, hence, to hidden hydrogen degradation of the materials.     

Stable Modelocking of a Coupled Cavity Moving Mirror Ring Dye Laser

Abstract

We report the stable operation of a new modelocked standing-wave ring dye laser operating with a repetition rate of 250 MHz. Two external cavities are coupled to a bidirectionally operating continuously pumped ring dye laser. When a moving mirror is placed in one of the external cavities, the laser produces pulses 6 ps in duration. The operation is stable with the modelocked pulses arriving in a constant intensity envelope 5 ms in duration at a repetition rate of 90 Hz.     

Dynamics of a Particle and a Quantized Vortex at Zero Temperature: Self-consistent Calculation

Many experiments for visualizing quantized vortices and normal fluid flow have been performed in superfluid ⁴He. Recently, metastable He₂ excimer molecules have been used as tracer particles. Since their radius is only about 10^?10 m, they hardly perturb the system, thus being a good candidate of tracer particles. In order to understand the interactive motion of He₂ molecules and vortices at zero temperature, we numerically study the trapping diameter by using the self-consistent equations of motions. We calculated the trapping diameter as a function of the initial velocity of the particle. The trapping diameter is almost inversely proportional to the initial velocity of the particle and compared with the observation.     

Numerical Modeling of Laminar Circulation Flow in a Cubic Cavity with a Moving Face

Laminar circulation flow in a cubic cavity with a moving face is numerically analyzed. The jetvortex elements of the flow which develop in the cavity are identified.     

Dynamics of Quantized Vortices in Superfluid Helium and Rotating Bose-Einstein Condensates

No Heading We study theoretically and numerically the dynamics of quantized vortices in superfluid helium and rotating Bose-Einstein condensates. After reviewing briefly the recent motivation, we discuss these topics with the emphasis on the research done by our group. One of the modern important problems is how superfluid turbulence relates to classical turbulence. First, we show that superfluid turbulence consisting of a vortex tangle has an energy spectrum consistent with the Kolmogorov law. Second, we discuss the vortex states that appear in a rotating channel with counterflow. In the field of atomic-gas Bose-Einstein condensation, the dramatic observations of quantized vortices were made for rotating condensates. By solving numerically the Gross-Pitaevskii equation, we found a whole story of the vortex lattice formation consistent with the observations.PACS numbers: 67.40.Vs, 47.32.Cc, 47.37.+q.     

Precursor Phenomena of Nucleations of Quantized Vortices in the Presence of a Uniformly Moving Obstacle in Bose-Einstein Condensates

We investigate excitations and fluctuations of Bose-Einstein condensates in a two-dimensional torus with a uniformly moving Gaussian potential by solving the Gross-Pitaevskii equation and the Bogoliubov equation. The energy gap Δ between the current-flowing metastable state (that reduces to the ground state for sufficiently slowly-moving potential) and the first excited state vanishes when the moving velocity v of the potential approaches a critical velocity $v_{\rm c}$ (>0). We find a scaling law $\Delta\propto(1-|v|/v_{\rm c})^{\frac{1}{4}}$ , which implies that a characteristic time scale diverges toward the critical velocity. Near the critical velocity, we show that low-energy local density fluctuations are enhanced. These behaviors can be regarded as precursor phenomena of the vortex nucleation.     

不同速度的移动质量作用下梁的动态响应分析

梁结构振动分析在各类工程中有着广泛的应用。本文主要针对在移动质量作用下Euler-Bernoulli简支梁对不同质量、速度下的响应。通过对运动方程的建立,用ANSYS进行有限元分析,对比简支梁中心点处的时间-位移曲线,研究速度与质量对振动过程的影响。     

Effects of Atomic Coherence on Collapses and Revivals in the Binomial State of the Field

Abstract

The effects of the coherence between the states of a two-level atom on the phenomenon of collapses and revivals in an undamped binomial state of the electromagnetic field are investigated. It is found that the Rabi oscillations exhibit qualitatively different behaviour for different phases of coherence between the levels. This behaviour in the binomial state of the field is in contrast with that in a coherent state field, in which case the Rabi oscillations are qualitatively the same for all values of the coherence between the two atomic levels.