Coulomb Drag Between Parallel Ballistic Quantum Wires

The Coulomb drag between parallel, {\it ballistic} quantum wires is studied theoretically in the presence of a perpendicular magnetic field B. The transresistance R_D shows peaks as a function of the Fermi level and splitting energy between the 1D subbands of the wires. The sharpest peaks appear when the Fermi level crosses the subband extrema so that the Fermi momenta are small. Two other kinds of peaks appear when either {\it intra}- or {\it inter}-subband transitions of electrons have maximum probability; the {\it intra}-subband transitions correspond to a small splitting energy. R_D depends on the field B in a nonmonotonic fashion: it decreases with B, as a result of the suppression of backscattering, and increases sharply when the Fermi level approaches the subband bottoms and the suppression is outbalanced by the increase of the Coulomb matrix elements and of the density of states.Comment: Text 14 pages in Latex/Revtex format, 4 Postscript figures. Phys. Rev. B,in pres

Novel CP-violating Effects in B decays from Charged-Higgs in a Two-Higgs Doublet Model for the Top Quark

We explore charged-Higgs cp-violating effects in a specific type III two-Higgs doublet model which is theoretically attractive as it accommodates the large mass of the top quark in a natural fashion. Two new CP-violating phases arise from the right-handed up quark sector. We consider CP violation in both neutral and charged B decays. Some of the important findings are as follows. 1) Large direct-CP asymmetry is found to be possible for B+- to psi/J K+-. 2) Sizable D-anti-D mixing effect at the percent level is found to be admissible despite the stringent constraints from the data on K-anti-K mixing, b to s gamma and B to tau nu decays. 3) A simple but distinctive CP asymmetry pattern emerges in decays of B_d and B_s mesons, including B_d to psi/J K_S, D+ D-, and B_s to D_s+ D_s-, psi eta/eta^prime, psi/J K_S. 4) The effect of D-anti-D mixing on the CP asymmetry in B+- to D/anti-D K+- and on the extraction of the angle gamma of the unitarity triangle from such decays can be significant.Comment: 32 pages, 5 figures, section V.A revised, version to appear in PR

Quantum teleportation of entangled coherent states

We propose a simple scheme for the quantum teleportation of both bipartite and multipartite entangled coherent states with the successful probability 1/2. The scheme is based on only linear optical devices such as beam splitters and phase shifters, and two-mode photon number measurements. The quantum channels described by multipartite maximally entangled coherent states are readily made by the beam splitters and phase shifters.Comment: 4 pages, no figure

On diagrammatic bounds of knot volumes and spectral invariants

In recent years, several families of hyperbolic knots have been shown to have both volume and $\lambda_1$ (first eigenvalue of the Laplacian) bounded in terms of the twist number of a diagram, while other families of knots have volume bounded by a generalized twist number. We show that for general knots, neither the twist number nor the generalized twist number of a diagram can provide two-sided bounds on either the volume or $\lambda_1$. We do so by studying the geometry of a family of hyperbolic knots that we call double coil knots, and finding two-sided bounds in terms of the knot diagrams on both the volume and on $\lambda_1$. We also extend a result of Lackenby to show that a collection of double coil knot complements forms an expanding family iff their volume is bounded.Comment: 16 pages, 7 figure

Nernst Effect in Electron-Doped Pr2−x_{2-x}Cex_{x}CuO4_4

The Nernst effect of Pr$_{2-x}$Ce$_{x}$CuO$_4$ (x=0.13, 0.15, and 0.17) has been measured on thin film samples between 5-120 K and 0-14 T. In comparison to recent measurements on hole-doped cuprates that showed an anomalously large Nernst effect above the resistive T$_c$ and H$_{c2}$ \cite{xu,wang1,wang2,capan}, we find a normal Nernst effect above T$_c$ and H$_{c2}$ for all dopings. The lack of an anomalous Nernst effect in the electron-doped compounds supports the models that explain this effect in terms of amplitude and phase fluctuations in the hole-doped cuprates. In addition, the H$_{c2}$(T) determined from the Nernst effect shows a conventional behavior for all dopings. The energy gap determined from H$_{c2}$(0) decreases as the system goes from under-doping to over-dopingin agreement with the recent tunnelling experiments

Multipartite entangled coherent states

We propose a scheme for generating multipartite entangled coherent states via entanglement swapping, with an example of a physical realization in ion traps. Bipartite entanglement of these multipartite states is quantified by the concurrence. We also use the $N$--tangle to compute multipartite entanglement for certain systems. Finally we establish that these results for entanglement can be applied to more general multipartite entangled nonorthogonal states.Comment: 7 pages, two figures. We added more detail discussions on the generation of multipartite entangled coherent states and multipartite entangelemen

Possible Z2 phase and spin-charge separation in electron doped cuprate superconductors

The SU(2) slave-boson mean-field theory for the tt'J model is analyzed. The role of next-nearest-neighbor hopping t' on the phase-diagram is studied. We find a pseudogap phase in hole-doped materials (where t'<0). The pseudo-gap phase is a U(1) spin liquid (the staggered-flux phase) with a U(1) gauge interaction and no fractionalization. This agrees with experiments on hole doped samples. The same calculation also indicates that a positive t' favors a Z2 state with true spin-charge separation. The Z2 state that exists when t' > 0.5J can be a candidate for the pseudo-gap phase of electron-doped cuprates (if such a phase exists). The experimental situation in electron-doped materials is also addressed.Comment: 6 pages, 2 figures, RevTeX4. Homepage http://dao.mit.edu/~wen

The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk

We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters and the selection effects that are caused by the photometric target preselection. We find that the colour and magnitude cuts in the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as high as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5 Gyr, Galactocentric distances from 6 kpc to 9.5 kpc, and vertical distances from the plane 0 < |Z| < 1.5 kpc. On this basis, we find that i) the observed age-metallicity relation is nearly flat in the range of ages between 0 Gyr and 8 Gyr; ii) at ages older than 9 Gyr, we see a decrease in [Fe/H] and a clear absence of metal-rich stars; this cannot be explained by the survey selection functions; iii) there is a significant scatter of [Fe/H] at any age; and iv) [Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages > 9 Gyr is not as small as advocated by some other studies. In agreement with earlier work, we find that radial abundance gradients change as a function of vertical distance from the plane. The [Mg/Fe] gradient steepens and becomes negative. In addition, we show that the inner disk is not only more alpha-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.Comment: accepted for publication in A&

Generation of maximum spin entanglement induced by cavity field in quantum-dot systems

Equivalent-neighbor interactions of the conduction-band electron spins of quantum dots in the model of Imamoglu et al. [Phys. Rev. Lett. 83, 4204 (1999)] are analyzed. Analytical solution and its Schmidt decomposition are found and applied to evaluate how much the initially excited dots can be entangled to the remaining dots if all of them are initially disentangled. It is demonstrated that the perfect maximally entangled states (MES) can only be generated in the systems of up to 6 dots with a single dot initially excited. It is also shown that highly entangled states, approximating the MES with a good accuracy, can still be generated in systems of odd number of dots with almost half of them being excited. A sudden decrease of entanglement is observed by increasing the total number of dots in a system with a fixed number of excitations.Comment: 6 pages, 7 figures, to appear in Phys. Rev.

Multiorder coherent Raman scattering of a quantum probe field

We study the multiorder coherent Raman scattering of a quantum probe field in a far-off-resonance medium with a prepared coherence. Under the conditions of negligible dispersion and limited bandwidth, we derive a Bessel-function solution for the sideband field operators. We analytically and numerically calculate various quantum statistical characteristics of the sideband fields. We show that the multiorder coherent Raman process can replicate the statistical properties of a single-mode quantum probe field into a broad comb of generated Raman sidebands. We also study the mixing and modulation of photon statistical properties in the case of two-mode input. We show that the prepared Raman coherence and the medium length can be used as control parameters to switch a sideband field from one type of photon statistics to another type, or from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.