1,020 research outputs found
Quantum phases of strongly-interacting bosons on a two-leg Haldane ladder
We study the ground-state physics of a single-component Haldane model on a
hexagonal two-leg ladder geometry with a particular focus on strongly
interacting bosonic particles. We concentrate our analysis on the regime of
less than one particle per unit-cell. As a main result, we observe several
Meissner-like and vortex-fluid phases both for a superfluid as well as a
Mott-insulating background. Furthermore, we show that for strongly interacting
bosonic particles an unconventional vortex-lattice phase emerges, which is
stable even in the regime of hardcore bosons. We discuss the mechanism for its
stabilization for finite interactions by a means of an analytical
approximation. We show how the different phases may be discerned by measuring
the nearest- and next-nearest-neighbor chiral currents as well as their
characteristic momentum distributions.Comment: 13 pages, 20 figure
Recommissionig of the Hyper-EBIT by measuring x-ray spectra of highly charged ions
Electron beam ion traps (EBIT) are experimental setups for the production, analysis and extraction of highly charged ions (HCI). High precision measurements of fundamental constants, like the g factor in the Penning-trap experiment Alphatrap, benefit from the properties of HCI. For inner shell electrons in heavy HCI, the electric field that the electron experiences close to the nucleus reaches values up to 10−16V/cm. Investigating this strong interaction by measuring the properties of the bound electron therefore allows to test QED in extreme conditions. An EBIT capable to inject hydrogenlike HCI up to uranium into the Alphatrap Penning-trap setup would allow these tests. In the scope of this thesis the Hyper-EBIT, intended to provide this capability in the future, was recommissioned. After a long shutdown all of the Hyper-EBITs critical components were tested. Further the space charge compensation of the beam was determined through the study of dielectric recombination of He-like to O-like argon ions. In the process the successful operation at moderate beam energies of 7 keV and beam currents of up to 120 mA was demonstrated. This serves as preparations for the aimed beam energies of 300 keV, as the necessary high voltage components are currently under development. <br
Relaxation and thermalization in the one-dimensional Bose-Hubbard model: A case study for the interaction quantum quench from the atomic limit
Motivated by recent experiments, we study the relaxation dynamics and
thermalization in the one-dimensional Bose-Hubbard model induced by a global
interaction quench. Specifically, we start from an initial state that has
exactly one boson per site and is the ground state of a system with infinitely
strong repulsive interactions at unit filling. Using exact diagonalization and
the density matrix renormalization group method, we compute the time dependence
of such observables as the multiple occupancy and the momentum distribution
function. Typically, the relaxation to stationary values occurs over just a few
tunneling times. The stationary values are identical to the so-called diagonal
ensemble on the system sizes accessible to our numerical methods and we further
observe that the micro-canonical ensemble describes the steady state of many
observables reasonably well for small and intermediate interaction strength.
The expectation values of observables in the canonical ensemble agree
quantitatively with the time averages obtained from the quench at small
interaction strengths, and qualitatively provide a good description of
steady-state values even in parameter regimes where the micro-canonical
ensemble is not applicable due to finite-size effects. We discuss our numerical
results in the framework of the eigenstate thermalization hypothesis. Moreover,
we also observe that the diagonal and the canonical ensemble are practically
identical for our initial conditions already on the level of their respective
energy distributions for small interaction strengths. Finally, we discuss
implications of our results for the interpretation of a recent sudden expansion
experiment [Phys. Rev. Lett. 110, 205301 (2013)], in which the same interaction
quench was realized.Comment: 19 pages, 22 figure
Modern Aerocapture Guidance to Enable Reduced-Lift Vehicles at Neptune
Aerocapture is covered extensively in the literature as means of achieving orbital insertion with dramatic mass-saving results compared to fully-propulsive systems. One of the primary obstacles facing aerocapture is the inherent uncertainty associated with passing through a planets upper atmosphere. In-flight dispersions due to delivery errors, environment variables, and aerodynamic performance impose a large flight envelope. System studies for aerocapture often select high lift-to-drag ratios to compensate for these uncertainties. However, modern predictor-corrector guidance strategies have shown promise in recent years to provide robust control schemes in-situ. These algorithms do not rely on a pre-calculated reference trajectory and instead employ a numerical optimizer to continuously solve nonlinear equations of motion each guidance cycle. Numerical predictor-corrector strategies may provide considerable accuracy over heritage guidance schemes. The goal of this study is reproduce a landmark study of Neptune aerocapture and apply modern guidance to illustrate relative performance improvements and cost-saving potential. Capture constraints based on the theoretical corridor width are considered. Results indicate that heritage vehicles with moderate lift-to-drag ratios, lower than previous studies have indicated, may prove viable for aerocapture at Neptune
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
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
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
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
Rethinking the Pipeline of Demosaicing, Denoising and Super-Resolution
Incomplete color sampling, noise degradation, and limited resolution are the
three key problems that are unavoidable in modern camera systems. Demosaicing
(DM), denoising (DN), and super-resolution (SR) are core components in a
digital image processing pipeline to overcome the three problems above,
respectively. Although each of these problems has been studied actively, the
mixture problem of DM, DN, and SR, which is a higher practical value, lacks
enough attention. Such a mixture problem is usually solved by a sequential
solution (applying each method independently in a fixed order: DM DN
SR), or is simply tackled by an end-to-end network without enough
analysis into interactions among tasks, resulting in an undesired performance
drop in the final image quality. In this paper, we rethink the mixture problem
from a holistic perspective and propose a new image processing pipeline: DN
SR DM. Extensive experiments show that simply modifying the usual
sequential solution by leveraging our proposed pipeline could enhance the image
quality by a large margin. We further adopt the proposed pipeline into an
end-to-end network, and present Trinity Enhancement Network (TENet).
Quantitative and qualitative experiments demonstrate the superiority of our
TENet to the state-of-the-art. Besides, we notice the literature lacks a full
color sampled dataset. To this end, we contribute a new high-quality full color
sampled real-world dataset, namely PixelShift200. Our experiments show the
benefit of the proposed PixelShift200 dataset for raw image processing.Comment: Code is available at: https://github.com/guochengqian/TENe
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