Loading of bosons in optical lattices into the p band

We present a method for transferring bosonic atoms residing on the lowest s-band of an optical lattice to the first excited p-bands. Our idea hinges on resonant tunneling between adjacent sites of accelerated lattices. The acceleration effectively shifts the quasi-bound energies on each site such that the system can be cast into a Wannier-Stark ladder problem. By adjusting the acceleration constant, a situation of resonant tunneling between the s- and p-bands is achievable. Within a mean-field model, considering 87Rb atoms, we demonstrate population transfer from the s- to the p-bands with around 95 % efficiency. Nonlinear effects deriving from atom-atom interactions, as well as coupling of the quasi bound Wannier-Stark states to the continuum, are considered.Comment: 8 pages, 7 figure

Bloch oscillations of Path-Entangled Photons

We show that when photons in N-particle path entangled |N,0> + |0,N> state undergo Bloch oscillations, they exhibit a periodic transition between spatially bunched and antibunched states. The transition occurs even when the photons are well separated in space. We study the scaling of the bunching-antibunching period, and show it is proportional to 1/N.Comment: An error in figure 1b of the original manuscript was corrected, and the period $\lambda_B$ was redefine

Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La(2-x)Sr(x)CuO(4)

By using new and previous measurements of the $ab$-plane conductivity $\sigma_1^{ab} (\omega,T)$ of La$_{2-x}$Sr$_x$CuO$_{4}$ (LSCO) it is shown that the spectral weight $W = \int_0^\Omega {\sigma_1^{ab} (\omega,T) d\omega}$ obeys the same law $W = W_0 - B(\Omega) T^2$ which holds for a conventional metal like gold, for $\Omega$'s below the plasma frequency. However $B(\Omega)$, which measures the "thermal response" of the charge system, in LSCO exhibits a peculiar behavior which points towards correlation effects. In terms of hopping models, $B(\Omega)$ is directly related to an energy scale $t_T$, smaller by one order of magnitude than the full bandwidth $t_0 \sim W_0$.Comment: 4 pages with 3 fig

Weak-field Hall effect and static polarizability of Bloch electrons

A theory of the weak field Hall effect of Bloch electrons based on the analysis of the forces acting on electrons is presented. It is argued that the electric current is composed of two contributions, that driven by the electric field along current flow and the non-dissipative contribution originated in demagnetization currents. The Hall resistance as a function of the electron concentration for the tight-binding model of a crystal with square lattice and body-centered cubic lattice is described in detail. For comparison the effect of strong magnetic fields is also discussed

Steering Magnetic Skyrmions with Nonequilibrium Green's Functions

Magnetic skyrmions, topologically protected vortex-like configurations in spin textures, are of wide conceptual and practical appeal for quantum information technologies, notably in relation to the making of so-called race-track memory devices. Skyrmions can be created, steered and destroyed with magnetic fields and/or (spin) currents. Here we focus on the latter mechanism, analyzed via a microscopic treatment of the skyrmion-current interaction. The system we consider is an isolated skyrmion in a square-lattice cluster, interacting with electrons spins in a current-carrying quantum wire. For the theoretical description, we employ a quantum formulation of spin-dependent currents via nonequilibrium Green's functions (NEGF) within the generalized Kadanoff-Baym ansatz (GKBA). This is combined with a treatment of skyrmions based on classical localized spins, with the skyrmion motion described via Ehrenfest dynamics. With our mixed quantum-classical scheme, we assess how time-dependent currents can affect the skyrmion dynamics, and how this in turn depends on electron-electron and spin-orbit interactions in the wire. Our study shows the usefulness of a quantum-classical treatment of skyrmion steering via currents, as a way for example to validate/extract an effective, classical-only, description of skyrmion dynamics from a microscopic quantum modeling of the skyrmion-current interaction.Comment: 10 pages, 8 figures, contribution to the proceedings of "Progress in Nonequilibrium Green's Functions VII

Designed Interaction Potentials via Inverse Methods for Self-Assembly

We formulate statistical-mechanical inverse methods in order to determine optimized interparticle interactions that spontaneously produce target many-particle configurations. Motivated by advances that give experimentalists greater and greater control over colloidal interaction potentials, we propose and discuss two computational algorithms that search for optimal potentials for self-assembly of a given target configuration. The first optimizes the potential near the ground state and the second near the melting point. We begin by applying these techniques to assembling open structures in two dimensions (square and honeycomb lattices) using only circularly symmetric pair interaction potentials ; we demonstrate that the algorithms do indeed cause self-assembly of the target lattice. Our approach is distinguished from previous work in that we consider (i) lattice sums, (ii) mechanical stability (phonon spectra), and (iii) annealed Monte Carlo simulations. We also devise circularly symmetric potentials that yield chain-like structures as well as systems of clusters.Comment: 28 pages, 23 figure

Flavor-twisted boundary condition for simulations of quantum many-body systems

We present an approximative simulation method for quantum many-body systems based on coarse graining the space of the momentum transferred between interacting particles, which leads to effective Hamiltonians of reduced size with the flavor-twisted boundary condition. A rapid, accurate, and fast convergent computation of the ground-state energy is demonstrated on the spin-1/2 quantum antiferromagnet of any dimension by employing only two sites. The method is expected to be useful for future simulations and quick estimates on other strongly correlated systems.Comment: 6 pages, 2 figure

Violation of the London Law and Onsager-Feynman quantization in multicomponent superconductors

Non-classical response to rotation is a hallmark of quantum ordered states such as superconductors and superfluids. The rotational responses of all currently known single-component "super" states of matter (superconductors, superfluids and supersolids) are largely described by two fundamental principles and fall into two categories according to whether the systems are composed of charged or neutral particles: the London law relating the angular velocity to a subsequently established magnetic field and the Onsager-Feynman quantization of superfluid velocity. These laws are theoretically shown to be violated in a two-component superconductor such as the projected liquid metallic states of hydrogen and deuterium at high pressures. The rotational responses of liquid metallic hydrogen or deuterium identify them as a new class of dissipationless states; they also directly point to a particular experimental route for verification of their existence.Comment: Nature Physics in print. This is an early version of the paper. The final version will be posted 6 months after its publication Nature Physics, according to the journal polic

Elusive electron-phonon coupling in quantitative analyses of the spectral function

We examine multiple techniques for extracting information from angle-resolved photoemission spectroscopy (ARPES) data, and test them against simulated spectral functions for electron-phonon coupling. We find that, in the low-coupling regime, it is possible to extract self-energy and bare-band parameters through a self-consistent Kramers-Kronig bare-band fitting routine. We also show that the effective coupling parameters deduced from the renormalization of quasiparticle mass, velocity, and spectral weight are momentum dependent and, in general, distinct from the true microscopic coupling; the latter is thus not readily accessible in the quasiparticle dispersion revealed by ARPES.Comment: A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/KKBF.pd