3,260 research outputs found

    Dynamic effects of electromagnetic wave on a damped two-level atom

    Get PDF
    We studied the dynamic effects of an electromagnetic(EM) wave with circular polarization on a two-level damped atom. The results demonstrate interesting ac Stark split of energy levels of damped atom. The split levels have different energies and lifetimes, both of which depend on the interaction and the damping rate of atom. When the frequency of the EM wave is tuned to satisfy the resonance condition in the strong coupling limit, the transition probability exhibits Rabi oscillation. Momentum transfer between atom and EM wave shows similar properties as the transition probability under resonance condition. For a damped atom interacting with EM field, there exists no longer stable state. More importantly, if the angular frequency of the EM wave is tuned the same as the atomic transition frequency and its amplitude is adjusted appropriately according to the damping coefficients, we can prepare a particular 'Dressed State' of the coupled system between atom and EM field and can keep the system coherently in this 'Dressed state' for a very long time. This opens another way to prepare coherent atomic states.Comment: latex, 2 figure

    Metastable behavior of vortex matter in the electronic transport processes of homogenous superconductors

    Get PDF
    We study numerically the effect of vortex pinning on the hysteresis voltage-temperature (V-T) loop of vortex matter. It is found that different types of the V-T loops result from different densities of vortex pinning center. An anticlockwise V-T loop is observed for the vortex system with dense pinning centers, whereas a clockwise V-T loop is brought about for vortices with dilute pinning centers. It is shown that the size of the V-T loop becomes smaller for lower experimental speed, higher magnetic field, or weak pinning strength. Our numerical observation is in good agreement with experiments

    Occurrence and risk assessment of polycyclic aromatic hydrocarbons in soil from the Tiefa coal mine district, Liaoning, China.

    Get PDF
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;In order to evaluate soil-associated polycyclic aromatic hydrocarbons (PAHs) pollution from coal mine activities in Tiefa coal mine, Northeast China, 16 PAHs identified as priority pollutants by US Environmental Pollution Agency were determined in mining zone soil (MZS), agricultural soil (AS), local lake bank soil (LBS), a vertical soil profile and three coal gangue samples. The total concentration of 16 PAHs (defined as &Sigma;(16)PAH, dry weight) in surface soil ranged from 5.1 to 5642.3 ng g(-1), with an arithmetic mean of 1118.3 ng g(-1). &Sigma;(16)PAH values at the sites from MZS are significantly higher than those found in AS and LBS. The vertical distribution of PAHs indicated that these compounds can penetrate the deeper layers of the soil, especially the low-rings compounds. A complex of petrogenic origin and pyrolytic sources was found within the study area, as suggested by the isomeric ratios of PAHs. According to principal component analysis (PCA), four factors were identified in the source contribution, including coal combustion, unburned coal particulates, coal gangue and vehicular emissions. The degree of contamination and the PAH toxicity assessment suggested that the soils of the study area have been seriously polluted and pose a high potential health risk.</span

    Weak force detection using a double Bose-Einstein condensate

    Get PDF
    A Bose-Einstein condensate may be used to make precise measurements of weak forces, utilizing the macroscopic occupation of a single quantum state. We present a scheme which uses a condensate in a double well potential to do this. The required initial state of the condensate is discussed, and the limitations on the sensitivity due to atom collisions and external coupling are analyzed.Comment: 12 pages, 2 figures, Eq.(41) has been correcte

    Collapse of ρxx\rho_{xx} ringlike structures in 2DEGs under tilted magnetic fields

    Full text link
    In the quantum Hall regime, the longitudinal resistivity ρxx\rho_{xx} plotted as a density--magnetic-field (n2DBn_{2D}-B) diagram displays ringlike structures due to the crossings of two sets of spin split Landau levels from different subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801 (2005)]. For tilted magnetic fields, some of these ringlike structures "shrink" as the tilt angle is increased and fully collapse at θc6\theta_c \approx 6^\circ. Here we theoretically investigate the topology of these structures via a non-interacting model for the 2DEG. We account for the inter Landau-level coupling induced by the tilted magnetic field via perturbation theory. This coupling results in anti-crossings of Landau levels with parallel spins. With the new energy spectrum, we calculate the corresponding n2DBn_{2D}-B diagram of the density of states (DOS) near the Fermi level. We argue that the DOS displays the same topology as ρxx\rho_{xx} in the n2DBn_{2D}-B diagram. For the ring with filling factor ν=4\nu=4, we find that the anti-crossings make it shrink for increasing tilt angles and collapse at a large enough angle. Using effective parameters to fit the θ=0\theta = 0^\circ data, we find a collapsing angle θc3.6\theta_c \approx 3.6^\circ. Despite this factor-of-two discrepancy with the experimental data, our model captures the essential mechanism underlying the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in August 2008 in Foz do Igua\c{c}u, Brazi
    corecore