7,166 research outputs found
Simulation of complete many-body quantum dynamics using controlled quantum-semiclassical hybrids
A controlled hybridization between full quantum dynamics and semiclassical
approaches (mean-field and truncated Wigner) is implemented for interacting
many-boson systems. It is then demonstrated how simulating the resulting hybrid
evolution equations allows one to obtain the full quantum dynamics for much
longer times than is possible using an exact treatment directly. A collision of
sodium BECs with 1.x10^5 atoms is simulated, in a regime that is difficult to
describe semiclassically. The uncertainty of physical quantities depends on the
statistics of the full quantum prediction. Cutoffs are minimised to a
discretization of the Hamiltonian. The technique presented is quite general and
extension to other systems is considered.Comment: Published version. Broader background and discussion, slightly
shortened, less figures in epaps. Research part unchanged. Article + epaps
(4+4 pages), 8 figure
Faraday waves in elongated superfluid fermionic clouds
We use hydrodynamic equations to study the formation of Faraday waves in a
superfluid Fermi gas at zero temperature confined in a strongly elongated
cigar-shaped trap. First, we treat the role of the radial density profile in
the limit of an infinite cylindrical geometry and analytically evaluate the
wavelength of the Faraday pattern. The effect of the axial confinement is fully
taken into account in the numerical solution of hydrodynamic equations and
shows that the infinite cylinder geometry provides a very good description of
the phenomena.Comment: 6 pages, 7 figures. Figures 4 and 6 in high resolution on reques
A New Superintegrable Hamiltonian
We identify a new superintegrable Hamiltonian in 3 degrees of freedom,
obtained as a reduction of pure Keplerian motion in 6 dimensions. The new
Hamiltonian is a generalization of the Keplerian one, and has the familiar 1/r
potential with three barrier terms preventing the particle crossing the
principal planes. In 3 degrees of freedom, there are 5 functionally independent
integrals of motion, and all bound, classical trajectories are closed and
strictly periodic. The generalisation of the Laplace-Runge-Lenz vector is
identified and shown to provide functionally independent isolating integrals.
They are quartic in the momenta and do not arise from separability of the
Hamilton-Jacobi equation. A formulation of the system in action-angle variables
is presented.Comment: 11 pages, 4 figures, submitted to The Journal of Mathematical Physic
Inducing topological order in a honeycomb lattice
We explore the possibility of inducing a topological insulator phase in a
honeycomb lattice lacking spin-orbit interaction using a metallic (or Fermi
gas) environment. The lattice and the metallic environment interact through a
density-density interaction without particle tunneling, and integrating out the
metallic environment produces a honeycomb sheet with in-plane oscillating
long-ranged interactions. We find the ground state of the interacting system in
a variational mean-field method and show that the Fermi wave vector, kF, of the
metal determines which phase occurs in the honeycomb lattice sheet. This is
analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in which the
metal's kF determines the interaction profile as a function of the distance.
Tuning kF and the interaction strength may lead to a variety of ordered phases,
including a topological insulator and anomalous quantum-hall states with
complex next-nearest-neighbor hopping, as in the Haldane and the Kane-Mele
model. We estimate the required range of parameters needed for the topological
state and find that the Fermi vector of the metallic gate should be of the
order of 3Pi/8a (with a being the graphene lattice constant). The net coupling
between the layers, which includes screening in the metal, should be of the
order of the honeycomb lattice bandwidth. This configuration should be most
easily realized in a cold-atoms setting with two interacting Fermionic species.Comment: 7 pages; 2 figures; Version 2 - added references; added an appendix
about screenin
Origin of the Heavy Fermion Behavior in Ca_{2-x}Sr_{x}RuO_{4}: Roles of Coulomb Interaction and the Rotation of RuO_{6} octahedra
We study the electronic states for Ca_{2-x}Sr_{x}RuO_{4} in within the Gutzwiller approximation (GA) on the basis of the three-orbital
Hubbard model for the Ru t_{2g} orbitals. The main effects of the Ca
substitution are taken account as the changes of the hybridizations
between the Ru 4d and O 2p orbitals. Using the numerical minimization of the
energy obtained in the GA, we obtain the renormalization factor (RF) of the
kinetic energy and total RF, which estimates the inverse of the mass
enhancement, for three cases with the effective models of x=2 and 0.5 and a
special model. We find that the inverse of the total RF becomes the largest for
the case of x=0.5, and that the van Hove singularity, which is located on
(below) the Fermi level for the special model (the effective model of x=0.5),
plays a secondary role in enhancing the effective mass. Our calculation
suggests that the heavy fermion behavior around x=0.5 comes from the
cooperative effects between moderately strong Coulomb interaction compared to
the total bandwidth and the modification of the electronic structures due to
the rotation of RuO_{6} octahedra (i.e., the variation of the
hybridizations and the downward shift for the orbital). We propose
that moderately strong electron correlation and the orbital-dependent
modifications of the electronic structures due to the lattice distortions play
important roles in the electronic states for Ca_{2-x}Sr_{x}RuO_{4}.Comment: 16 pages, 13 figures, 1 table, accepted for publication in Physical
Review B; added the discussions both about the validity of the present
treatment and about Hund's metal in this allo
Coupled dynamics of atoms and radiation pressure driven interferometers
We consider the motion of the end mirror of a cavity in whose standing wave
mode pattern atoms are trapped. The atoms and the light field strongly couple
to each other because the atoms form a distributed Bragg mirror with a
reflectivity that can be fairly high. We analyze how the dipole potential in
which the atoms move is modified due to this backaction of the atoms. We show
that the position of the atoms can become bistable. These results are of a more
general nature and can be applied to any situation where atoms are trapped in
an optical lattice inside a cavity and where the backaction of the atoms on the
light field cannot be neglected. We analyze the dynamics of the coupled system
in the adiabatic limit where the light field adjusts to the position of the
atoms and the light field instantaneously and where the atoms move much faster
than the mirror. We calculate the side band spectrum of the light transmitted
through the cavity and show that these spectra can be used to detect the
coupled motion of the atoms and the mirror.Comment: 11 pages; 13 figures; two added references and other minor
correction
Interacting dark matter and modified holographic Ricci dark energy induce a relaxed Chaplygin gas
We investigate a model of interacting dark matter and dark energy given by a
modified holographic Ricci cutoff in a spatially flat
Friedmann-Robertson-Walker (FRW) space-time. We consider a nonlinear
interaction consisting of a significant rational function of the total energy
density and its first derivative homogeneous of degree one and show that the
effective one-fluid obeys the equation of state of a relaxed Chaplygin gas. So
that, the universe is dominated by pressureless dark matter at early times and
undergoes an accelerated expansion in the far future driven by a strong
negative pressure. We apply the -statistical method to the
observational Hubble data and the Union2 compilation of SNe Ia for constraining
the cosmological parameters and analyze the feasibility of the modified
holographic Ricci cutoff. By using the new diagnostic method, we find that
the effective model differs substantially from the --CDM one, because
it gets the accelerated expansion faster than the --CDM model.
Finally, a new model with a third component decoupled from the interacting dark
sector is presented for studying bounds on the dark energy at early times.Comment: 8 pages, 7 figures. Revtex4 Style. Accepted for its publication in
PR
The motion of the freely falling chain tip
The dynamics of the tip of the falling chain is analyzed. Results of
laboratory experiments are presented and compared with results of numerical
simulations. Time dependences of the velocity and the acceleration of the chain
tip for a number of different initial conformations of the chain are
determined. A simple analytical model of the system is also considered.Comment: 29 pages, 13 figure
A hybrid model for Rydberg gases including exact two-body correlations
A model for the simulation of ensembles of laser-driven Rydberg-Rydberg
interacting multi-level atoms is discussed. Our hybrid approach combines an
exact two-body treatment of nearby atom pairs with an effective approximate
treatment for spatially separated pairs. We propose an optimized evolution
equation based only on the system steady state, and a time-independent Monte
Carlo technique is used to efficiently determine this steady state. The hybrid
model predicts features in the pair correlation function arising from
multi-atom processes which existing models can only partially reproduce. Our
interpretation of these features shows that higher-order correlations are
relevant already at low densities. Finally, we analyze the performance of our
model in the high-density case.Comment: significantly expanded and revised version (more observables,
high-density regime); 9 pages, 8 figure
Ab initio mass tensor molecular dynamics
Mass tensor molecular dynamics was first introduced by Bennett [J. Comput.
Phys. 19, 267 (1975)] for efficient sampling of phase space through the use of
generalized atomic masses. Here, we show how to apply this method to ab initio
molecular dynamics simulations with minimal computational overhead. Test
calculations on liquid water show a threefold reduction in computational effort
without making the fixed geometry approximation. We also present a simple
recipe for estimating the optimal atomic masses using only the first
derivatives of the potential energy.Comment: 19 pages, 5 figure
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