Dynamics of a two-level system under the simultaneous influence of a spin bath and a boson bath

We study dynamics of a two-level system coupled simultaneously to a pair of dissimilar reservoirs, namely, a spin bath and a boson bath, which are connected via finite interbath coupling. It is found that the steady-state energy transfer in the two-level system increases with its coupling to the spin bath while optimal transfer occurs at intermediate coupling in the transient process. If the two-level system is strongly coupled to the spin bath, the population transfer is unidirectional barring minor population oscillations of minute amplitudes. If the spin bath is viewed as an atomic ensemble, robust generation of macroscopic superposition states exists against parameter variations of the two-level system and the boson bath.Comment: 12 pages, 4 figure

One-loop QCD correction to top pair production in the littlest Higgs model with T-parity at the LHC

In this work, we investigate the one-loop QCD correction to top pair production in the littlest Higgs model with T-parity at the LHC. We calculate the relative correction of the top pair production cross section and top-antitop spin correlation at the LHC for $\sqrt{s}=8,14$ TeV. We find that the relative corrections of top pair production cross section can reach about $-0.35\%$, and the top-antitop spin correlation can reach $1.7\%$($2\%$) at the 8(14) TeV LHC in the favorable parameter space

Synchrotron diffraction studies of spontaneous magnetostriction in rare earth transition metal compounds

Thermal expansion anomalies of R2Fe14B and R 2Fe17Cx (x = 0, 2) (R = Y, Nd, Gd, Tb, Er) stoichiometric compounds are studied with high-energy synchrotron X-ray powder diffraction using Debye-Scherrer geometry in temperature range 10K to 1000K. Large spontaneous magnetostriction up to their Curie temperatures (Tc) is observed. The a-axes show relatively larger invar effects than c-axes in the R 2Fe14B compounds whereas the R2Fe17C x show the contrary anisotropies. The iron sub-lattice is shown to dominate the spontaneous magnetostriction of the compounds. The contribution of the rare earth sublattice is roughly proportional to the spin magnetic moment of the rare earth in the R2Fe14B compounds but in R 2Fe17Cx, the rare earth sub-lattice contribution appears more likely to be dominated by the local bonding. The calculation of spontaneous magnetostrain of bonds shows that the bonds associated with Fe(j2) sites in R2Fe14B and the dumbbell sites in R 2Fe17Cx have larger values, which is strongly related to their largest magnetic moment and Wigner-Seitz atomic cell volume. The roles of the carbon atoms in increasing the Curie temperatures of the R2Fe17 compounds are attributed to the increased separation of Fe hexagons. The R2Fe17 and R2Fe 14B phases with magnetic rare earth ions also show anisotropies of thermal expansion above Tc. For R2Fe17 and R 2Fe14B the alphaa/alphac \u3e 1 whereas the anisotropy is reversed with the interstitial carbon in R2Fe 17. The average bond magnetostrain is shown to be a possible predictor of the magnetic moment of Fe sites in the compounds. Both of the theoretical and phenomenological models on spontaneous magnetostriction are discussed and a Landau model on the spontaneous magnetostriction is proposed