776 research outputs found
Scrambling and thermalization in a diffusive quantum many-body system
Out-of-time ordered (OTO) correlation functions describe scrambling of
information in correlated quantum matter. They are of particular interest in
incoherent quantum systems lacking well defined quasi-particles. Thus far, it
is largely elusive how OTO correlators spread in incoherent systems with
diffusive transport governed by a few globally conserved quantities. Here, we
study the dynamical response of such a system using high-performance
matrix-product-operator techniques. Specifically, we consider the
non-integrable, one-dimensional Bose-Hubbard model in the incoherent
high-temperature regime. Our system exhibits diffusive dynamics in time-ordered
correlators of globally conserved quantities, whereas OTO correlators display a
ballistic, light-cone spreading of quantum information. The slowest process in
the global thermalization of the system is thus diffusive, yet information
spreading is not inhibited by such slow dynamics. We furthermore develop an
experimentally feasible protocol to overcome some challenges faced by existing
proposals and to probe time-ordered and OTO correlation functions. Our study
opens new avenues for both the theoretical and experimental exploration of
thermalization and information scrambling dynamics.Comment: 7+4 pages, 8+3 figures; streamlined versio
Angle-resolved photoemission spectroscopy with quantum gas microscopes
Quantum gas microscopes are a promising tool to study interacting quantum
many-body systems and bridge the gap between theoretical models and real
materials. So far they were limited to measurements of instantaneous
correlation functions of the form , even though
extensions to frequency-resolved response functions would provide important information about the elementary
excitations in a many-body system. For example, single particle spectral
functions, which are usually measured using photoemission experiments in
electron systems, contain direct information about fractionalization and the
quasiparticle excitation spectrum. Here, we propose a measurement scheme to
experimentally access the momentum and energy resolved spectral function in a
quantum gas microscope with currently available techniques. As an example for
possible applications, we numerically calculate the spectrum of a single hole
excitation in one-dimensional models with isotropic and anisotropic
antiferromagnetic couplings. A sharp asymmetry in the distribution of spectral
weight appears when a hole is created in an isotropic Heisenberg spin chain.
This effect slowly vanishes for anisotropic spin interactions and disappears
completely in the case of pure Ising interactions. The asymmetry strongly
depends on the total magnetization of the spin chain, which can be tuned in
experiments with quantum gas microscopes. An intuitive picture for the observed
behavior is provided by a slave-fermion mean field theory. The key properties
of the spectra are visible at currently accessible temperatures.Comment: 16+7 pages, 10+2 figure
Extended self-energy functional approach for strongly-correlated lattice bosons in the superfluid phase
Among the various numerical techniques to study the physics of strongly
correlated quantum many-body systems, the self-energy functional approach (SFA)
has become increasingly important. In its previous form, however, SFA is not
applicable to Bose-Einstein condensation or superfluidity. In this paper we
show how to overcome this shortcoming. To this end we identify an appropriate
quantity, which we term , that represents the correlation correction of the
condensate order parameter, as it does the self-energy for the Green's
function. An appropriate functional is derived, which is stationary at the
exact physical realizations of and of the self-energy. Its derivation is
based on a functional-integral representation of the grand potential followed
by an appropriate sequence of Legendre transformations. The approach is not
perturbative and therefore applicable to a wide range of models with local
interactions. We show that the variational cluster approach based on the
extended self-energy functional is equivalent to the "pseudoparticle" approach
introduced in Phys. Rev. B, 83, 134507 (2011). We present results for the
superfluid density in the two-dimensional Bose-Hubbard model, which show a
remarkable agreement with those of Quantum-Monte-Carlo calculations.Comment: 1 additional figure showing the region close to the tip of the Mott
lobe, minor changes in the tex
Self-consistent Hartree-Fock approach to many-body localization
In this work, we develop a self-consistent Hartree-Fock approach to
theoretically study the far-from-equilibrium quantum dynamics of interacting
fermions, and apply this approach to explore the onset of many-body
localization (MBL) in these systems. We investigate the dynamics of a state
with a nonequilibrium density profile; we find that at weak disorder the
density profile equilibrates rapidly, whereas for strong disorder it remains
frozen on the accessible timescales. We analyze this behavior in terms of the
Hartree-Fock self-energy. At weak disorder the self-energy fluctuates strongly
and can be interpreted as a self-consistent noise process. By contrast, at
strong disorder the self-energy evolves with a few coherent oscillations which
cannot delocalize the system. Accordingly, the non-equilibrium site-resolved
spectral function shows a broad spectrum at weak disorder and sharp spikes at
strong disorder. Our Hartree-Fock theory incorporates spatial fluctuations and
rare-region effects. As a consequence, we find subdiffusive relaxation in
random systems; but, when the system is subjected to weak quasi-periodic
potentials, the subdiffusive response ceases to exist, as rare region effects
are absent in this case. This self-consistent Hartree-Fock approach can be
regarded as a relatively simple theory that captures much of the MBL
phenomenology.Comment: 11 pages, 10 figures, Added references and expanded discussion
Terahertz Radiation Detection by Field Effect Transistor in Magnetic Field
We report on terahertz radiation detection with InGaAs/InAlAs Field Effect
Transistors in quantizing magnetic field. The photovoltaic detection signal is
investigated at 4.2 K as a function of the gate voltage and magnetic field.
Oscillations analogous to the Shubnikov-de Haas oscillations, as well as their
strong enhancement at the cyclotron resonance, are observed. The results are
quantitatively described by a recent theory, showing that the detection is due
to rectification of the terahertz radiation by plasma waves related
nonlinearities in the gated part of the channel.Comment: 4 pages, 3 figure
Cavity-mediated coupling of antiferromagnetic spin waves
Coupling of space-separated oscillators is interesting for quantum and
communication technologies. In this work, it is shown that two
antiferromagnetic oscillators placed inside an electromagnetic cavity couple
cooperatively to its terahertz modes and, in effect, hybridized
magnon-polariton modes are formed. This is supported by a systematic study of
reflection spectra from two parallel-plane slabs of hematite
(-FeO), measured as a function of their temperatures and
separation distance, and modeled theoretically. The mediating cavity was formed
by the crystals themselves and the experiment was performed in a practical
distance range of a few millimetres and above room temperature. Cavity-mediated
coupling allows for engineering of complex resonators controlled by their
geometry and by sharing properties of their components
Co-evolution of RDF Datasets
Linking Data initiatives have fostered the publication of large number of RDF
datasets in the Linked Open Data (LOD) cloud, as well as the development of
query processing infrastructures to access these data in a federated fashion.
However, different experimental studies have shown that availability of LOD
datasets cannot be always ensured, being RDF data replication required for
envisioning reliable federated query frameworks. Albeit enhancing data
availability, RDF data replication requires synchronization and conflict
resolution when replicas and source datasets are allowed to change data over
time, i.e., co-evolution management needs to be provided to ensure consistency.
In this paper, we tackle the problem of RDF data co-evolution and devise an
approach for conflict resolution during co-evolution of RDF datasets. Our
proposed approach is property-oriented and allows for exploiting semantics
about RDF properties during co-evolution management. The quality of our
approach is empirically evaluated in different scenarios on the DBpedia-live
dataset. Experimental results suggest that proposed proposed techniques have a
positive impact on the quality of data in source datasets and replicas.Comment: 18 pages, 4 figures, Accepted in ICWE, 201
Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications
Resonant frequencies of the two-dimensional plasma in FETs increase with the
reduction of the channel dimensions and can reach the THz range for sub-micron
gate lengths. Nonlinear properties of the electron plasma in the transistor
channel can be used for the detection and mixing of THz frequencies. At
cryogenic temperatures resonant and gate voltage tunable detection related to
plasma waves resonances, is observed. At room temperature, when plasma
oscillations are overdamped, the FET can operate as an efficient broadband THz
detector. We present the main theoretical and experimental results on THz
detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape
Submerged entry nozzle clogging during continuous casting of Al-killed steel
Nozzle clogging is a common problem in the production of continuously cast Al-killed steels. Clogging occurs when there are solid inclusions in molten steel at casting temperatures. SENs (Submerged entry nozzles) from continuous casting of Al-killed low alloy steel grades with increased content of sulfur (0,020 to 0,035 % S) were examined. The examinations revealed that the deposits are mainly alumina based, with spinel and sulfur inclusions and some entrapped steel melt. It was concluded that the process of clogging begins when the steel melt infiltrates the refractory and removes the protective zirconia surface, thus allowing the adhesion of fine solid aluminates, which form the deposits
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