1,245 research outputs found
Comparative study of theoretical methods for nonequilibrium quantum transport
We present a detailed comparison of three different methods designed to
tackle nonequilibrium quantum transport, namely the functional renormalization
group (fRG), the time-dependent density matrix renormalization group (tDMRG),
and the iterative summation of real-time path integrals (ISPI). For the
nonequilibrium single-impurity Anderson model (including a Zeeman term at the
impurity site), we demonstrate that the three methods are in quantitative
agreement over a wide range of parameters at the particle-hole symmetric point
as well as in the mixed-valence regime. We further compare these techniques
with two quantum Monte Carlo approaches and the time-dependent numerical
renormalization group method.Comment: 19 pages, 7 figures; published versio
Vortex and Meissner phases of strongly-interacting bosons on a two-leg ladder
We establish the phase diagram of the strongly-interacting Bose-Hubbard model
defined on a two-leg ladder geometry in the presence of a homogeneous flux. Our
work is motivated by a recent experiment [Atala et al., Nature Phys. 10, 588
(2014)], which studied the same system, in the complementary regime of weak
interactions. Based on extensive density matrix renormalization group
simulations and a bosonization analysis, we fully explore the parameter space
spanned by filling, inter-leg tunneling, and flux. As a main result, we
demonstrate the existence of gapless and gapped Meissner and vortex phases,
with the gapped states emerging in Mott-insulating regimes. We calculate
experimentally accessible observables such as chiral currents and vortex
patterns.Comment: 4 pages + Supplementary Materia
Spontaneous increase of magnetic flux and chiral-current reversal in bosonic ladders: Swimming against the tide
The interplay between spontaneous symmetry breaking in many-body systems, the
wavelike nature of quantum particles and lattice effects produces an
extraordinary behavior of the chiral current of bosonic particles in the
presence of a uniform magnetic flux defined on a two-leg ladder. While
non-interacting as well as strongly interacting particles, stirred by the
magnetic field, circulate along the system's boundary in the counterclockwise
direction in the ground state, interactions stabilize vortex lattices. These
states break translational symmetry, which can lead to a reversal of the
circulation direction. Our predictions could readily be accessed in quantum gas
experiments with existing setups or in arrays of Josephson junctions.Comment: 5 pages + 5 pages of supplementary materia
Comparison of regional blood flow values measured by radioactive and fluorescent microspheres
Fluorescent microspheres (FM) have become an attractive alternative to radioactive microspheres (RM) for the measurement of regional blood flow (RBF). The aim of the present study was to investigate the comparability of both methods by measuring RBF with FM and RM. Eight anaesthetised pigs received simultaneous, left atrial injections of FM and RM with a diameter of 15 mum at six different time points. Blood reference samples were collected from the descending aorta. RBF was determined in tissue samples of the myocardium, spleen and kidneys of all 8 animals. After radioactivity of the tissue samples was determined, the samples were processed automatically for measuring fluorescence using a recently developed filter device (SPU). RBF was calculated with both the isotope and spectrometric data of both methods for each sample resulting in a total of 10,512 blood flow values. The comparison of the RBF values yielded high linear correlation (mean r(2) = 0.95 +/- 0.03 to 0.97 +/- 0.02) and excellent agreement (bias 5.4-6.7%, precision 9.9-16.5%) of both methods. Our results indicate the validity of MS and of the automated tissue processing technique by means of the SPU. Copyright (C) 2002 S. Karger AG, Basel
Structure of the near-surface layer of NiTi on the meso- and microscale levels after ion-beam surface treatment
Using the EBSD, SEM and TEM methods, the structure of surface layer of polycrystalline NiTi alloy samples was examined after the modification of material surface by the pulsed action of mean-energy silicon ion beam. It was found that the ion beam treatment would cause grain fragmentation of the near-surface layer to a depth 5-50 [mu]m; a higher extent of fragmentation was observed in grains whose close-packed planes were oriented approximately in the same direction as the ion beam was. The effect of high-intensity ion beam treatment on the anisotropic behavior of polycrystalline NiTi alloy and the mechanisms involved were also examined
Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta
Long-range order in quantum many-body systems is usually associated with
equilibrium situations. Here, we experimentally investigate the
quasicondensation of strongly-interacting bosons at finite momenta in a
far-from-equilibrium case. We prepare an inhomogeneous initial state consisting
of one-dimensional Mott insulators in the center of otherwise empty
one-dimensional chains in an optical lattice with a lattice constant . After
suddenly quenching the trapping potential to zero, we observe the onset of
coherence in spontaneously forming quasicondensates in the lattice. Remarkably,
the emerging phase order differs from the ground-state order and is
characterized by peaks at finite momenta in the
momentum distribution function.Comment: See also Viewpoint: Emerging Quantum Order in an Expanding Gas,
Physics 8, 99 (2015
Exact results for nonlinear ac-transport through a resonant level model
We obtain exact results for the transport through a resonant level model
(noninteracting Anderson impurity model) for rectangular voltage bias as a
function of time. We study both the transient behavior after switching on the
tunneling at time t = 0 and the ensuing steady state behavior. Explicit
expressions are obtained for the ac-current in the linear response regime and
beyond for large voltage bias. Among other effects, we observe current ringing
and PAT (photon assisted tunneling) oscillations.Comment: 7 page
Expansion velocity of a one-dimensional, two-component Fermi gas during the sudden expansion in the ballistic regime
We show that in the sudden expansion of a spin-balanced two-component Fermi
gas into an empty optical lattice induced by releasing particles from a trap,
over a wide parameter regime, the radius of the particle cloud grows
linearly in time. This allow us to define the expansion velocity from
. The goal of this work is to clarify the dependence of the
expansion velocity on the initial conditions which we establish from
time-dependent density matrix renormalization group simulations, both for a box
trap and a harmonic trap. As a prominent result, the presence of a
Mott-insulating region leaves clear fingerprints in the expansion velocity. Our
predictions can be verified in experiments with ultra-cold atoms.Comment: 8 pages 10 figures, version as published with minor stylistic change
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