Non-Markovian disentanglement dynamics of two-qubit system

We investigated the disentanglement dynamics of two-qubit system in Non-Markovian approach. We showed that only the couple strength with the environment near to or less than fine-structure constant 1/137, entanglement appear exponential decay for a certain class of two-qubit entangled state. While the coupling between qubit and the environment is much larger, system always appears the sudden-death of entanglement even in the vacuum environment.Comment: 17 pages, 3 figure

Wigner crystal states for the two-dimensional electron gas in a double quantum well system

Using the Hartree-Fock approximation, we calculate the energy of different Wigner crystal states for the two-dimensional electron gas of a double quantum well system in a strong magnetic field. Our calculation takes interlayer hopping as well as an in-plane magnetic field into consideration. The ground The ground state at small layer separations is a one-component triangular lattice Wigner state. As the layer separation is increased, the ground state first undergoes a transition to two stacked square lattices, and then undergoes another transition at an even larger layer separation to a two-component triangular lattice. The range of the layer separation at which the two-component square lattice occurs as the ground state shrinks, and eventually disappears, as the interlayer hopping is increased. An in-plane magnetic field induces another phase transition from a commensurate to a incommensurate state, similar to that of $\nu=1$ quantum Hall state observed recently. We calculate the critical value of the in-plane field of the transition and find that the anisotropy of the Wigner state, {\it i.e.,}, the relative orientation of the crystal and the in-plane magnetic field, has a negligible effect on the critical value for low filling fractions. The effect of this anisotropy on the low-lying phonon energy is discussed. A novel exerimental geometry is proposed in which the parallel magnetic field is used to enhance the orientational correlations in the ground state when the crystal is subject toa random potential.Comment: RevTex 3.0, 22pages, 3figures available upon request. ukcm-xxx

On the Mass-to-Light Ratio of Large Scale Structure

We examine the dependence of the mass-to-light (M/L) ratio of large-scale structure on cosmological parameters, in models that are constrained to match observations of the projected galaxy correlation function w(rp). For a sequence of cosmological models with a fixed P(k) shape and increasing normalization \sig8, we find parameters of the galaxy halo occupation distribution (HOD) that reproduce SDSS measurements of w(rp) as a function of luminosity. Using these HOD models we calculate mean M/L ratios as a function of halo mass and populate halos of N-body simulations to compute M/L in larger scale environments, including cluster infall regions. For all cosmological models, the M/L ratio in high mass halos or high density regions is approximately independent of halo mass or smoothing scale. However, the "plateau" value of M/L depends on \sig8 as well as \Omega_m, and it represents the universal mass-to-light ratio only for models in which the galaxy correlation function is approximately unbiased, i.e., with \sig8 ~ \sig8_gal. Our results for cluster mass halos follow the trend M/L = 577(\Omega_m/0.3)(\sig8/0.9)^{1.7} h Msun/Lsun. Combined with Carlberg et al.'s (1996) mean M/L ratio of CNOC galaxy clusters, this relation implies (\sig8/0.9)(\Omega_m/0.3)^{0.6} = 0.75 +/- 0.06. M/L ratios of clusters from the SDSS and CAIRNS surveys yield similar results. This constraint is inconsistent with parameter values \Omega_m ~ 0.3, \sig8 ~ 0.9 favored by recent joint analyses of CMB measurements and other large-scale structure data. We discuss possible resolutions, none of which seems entirely satisfactory. Appendices present an improved formula for halo bias factors and an improved analytic technique for calculating the galaxy correlation function from a given cosmological model and HOD. (Abridged)Comment: Accepted to ApJ (v 630, no 2). Replaced with accepted versio