2,492 research outputs found
Light cone in the two-dimensional transverse-field Ising model in time-dependent mean-field theory
We investigate the propagation of a local perturbation in the two-dimensional
transverse-field Ising model with a time-dependent application of mean-field
theory based on the BBGKY hierarchy. We show that the perturbation propagates
through the system with a finite velocity and that there is transition from
Manhattan to Euclidian metric, resulting in a light cone with an almost
circular shape at sufficiently large distances. The propagation velocity of the
perturbation defining the front of the light cone is discussed with respect to
the parameters of the Hamiltonian and compared to exact results for the
transverse-field Ising model in one dimension.Comment: 6 pages, 4 figure
Quantum relaxation and metastability of lattice bosons with cavity-induced long-range interactions
The coupling of cold atoms to the radiation field within a high-finesse
optical resonator, an optical cavity, induces long-range interactions which can
compete with an underlying optical lattice. The interplay between short- and
long-range interactions gives rise to new phases of matter including
supersolidity (SS) and density waves (DW), and interesting quantum dynamics.
Here it is shown that for hard-core bosons in one dimension the ground state
phase diagram and the quantum relaxation after sudden quenches can be
calculated exactly in the thermodynamic limit. Remanent DW order is observed
for quenches from a DW ground state into the superfluid (SF) phase below a
dynamical transition line. After sufficiently strong SF to DW quenches beyond a
static metastability line DW order emerges on top of remanent SF order, giving
rise to a dynamically generated supersolid state.Comment: 6 pages, 5 figure
How performance based payoffs influence estimates of complex information? An experimental study on quality and precision in estimation tasks
This paper investigates the processing of repeated complex information. The focus of this study is, whether additional information and the introduction of performance-based payoffs have an influence on judgement. Therefore, an experiment is designed to investigate the degree of precision and quality of interval estimates. The data shows that providing additional information decreases the precision of stated estimates, while it improves its quality. The same result is obtained, when performance-based payoffs are introduced to an otherwise hypothetical decision environment. That means, while the variation in the treatment variables increase the quality of the estimate, the precision as a reflection of the decision makers confidence is reduced. --interval estimates,uncertainty,judgmental estimation,repeated information,hypothetical versus payoffs,experiment
Quantum relaxation and finite size effects in the XY chain in a transverse field after global quenches
We consider global quenches in the quantum XY chain in a transverse field and
study the nonequilibrium relaxation of the magnetization and the correlation
function as well as the entanglement entropy in finite systems. For quenches in
the ordered phase, the exact results are well described by a semiclassical
theory (SCT) in terms of ballistically moving quasiparticles. In the
thermodynamic limit the SCT is exact for the entanglement entropy and its
modified version following the method of Calabrese, Essler and Fagotti:
arXiv:1204.3911 is exact for the magnetization and the correlation function,
too. The stationary correlation function is shown to be described by a
generalized Gibbs ensemble.Comment: 6 pages, 4 figure
MBE Growth of Al/InAs and Nb/InAs Superconducting Hybrid Nanowire Structures
We report on \textit{in situ} growth of crystalline Al and Nb shells on InAs
nanowires. The nanowires are grown on Si(111) substrates by molecular beam
epitaxy (MBE) without foreign catalysts in the vapor-solid mode. The metal
shells are deposited by electron-beam evaporation in a metal MBE. High quality
supercondonductor/semiconductor hybrid structures such as Al/InAs and Nb/InAs
are of interest for ongoing research in the fields of gateable Josephson
junctions and quantum information related research. Systematic investigations
of the deposition parameters suitable for metal shell growth are conducted. In
case of Al, the substrate temperature, the growth rate and the shell thickness
are considered. The substrate temperature as well as the angle of the impinging
deposition flux are explored for Nb shells. The core-shell hybrid structures
are characterized by electron microscopy and x-ray spectroscopy. Our results
show that the substrate temperature is a crucial parameter in order to enable
the deposition of smooth Al layers. Contrary, Nb films are less dependent on
substrate temperature but strongly affected by the deposition angle. At a
temperature of 200{\deg}C Nb reacts with InAs, dissolving the nanowire crystal.
Our investigations result in smooth metal shells exhibiting an impurity and
defect free, crystalline superconductor/InAs interface. Additionally, we find
that the superconductor crystal structure is not affected by stacking faults
present in the InAs nanowires.Comment: 8 pages, 10 figures, 1 tabl
Extending teleoperated driving using a shared X-in-the-loop environment
The strong progress in modern vehicle system technology requires new methodological approaches for the development and validation of new vehicle systems. In particular, due to increasing automation, classical development methods and testing scenarios need to be evolved. Consequently, the publication focuses on an extension of teleoperated driving by the X-in-the-loop (XIL) approach. Within this framework, the classical concept based on VPN-LTE networking is analyzed and discussed at first. With this implementation, the remote control of a real vehicle is presented based on the use of a dynamic driving simulator. Especially for the development and validation of such concepts, an extension with the XIL methodology can improve this process. For this reason, the architecture of teleoperated driving is subsequently extended by networking with additional system components. The feasibility, the functionalities as well as the challenges that arise with such an extension based on the XIL methodology are shown.Within the scope of this study, the achieved transmission times for the control variables and for the video data stream are demonstrated. Based on different driving maneuvers, the achievable repeatability is discussed
Centaurus A at Ultra-High Energies
We review the importance of Centaurus A in high energy astrophysics as a
nearby object with many of the properties expected of a major source of very
high energy cosmic rays and gamma-rays. We examine observational techniques and
the results so far obtained in the energy range from 200 GeV to above 100 EeV
and attempt to fit those data with expectations of Centaurus A as an
astrophysical source from VHE to UHE energies.Comment: 11 pages, 4 figures, accepted for publication in PAS
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