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A Generic Communications Module for Cooperative 3D Visualization and Modelling over the Internet: the Collaborative API
Cooperative three-dimensional visualization and modeling applications allow a distributed group of users to work together with a model they share. To implement this kind of applications the underlying communications system must provide reliable and ordered multicast of users interactions. Due to the high complexity that characterizes the models, network bandwidth requirements have limited their use to intranets or in a few cases to very high-speed Internet connections.
In this paper we present a communications module that solves this problem. The library exposed, which is called Collaborative API, supports the creation of very efficient cooperative 3D visualization and modeling applications by optimizing the use of the network resources.
The Collaborative API, implements a new communications architecture: the dynamic client/server. The communications module presented in this paper is illustrated by two examples of applications that use it to provide cooperative 3D visualization over the Internet
Quantum versus classical counting in nonMarkovian master equations
We discuss the description of full counting statistics in quantum transport
with a nonMarkovian master equation. We focus on differences arising from
whether charge is considered as a classical or a quantum degree of freedom.
These differences manifest themselves in the inhomogeneous term of the master
equation which describes initial correlations. We describe the influence on
current and in particular, the finite-frequency shotnoise. We illustrate these
ideas by studying transport through a quantum dot and give results that include
both sequential and cotunneling processes. Importantly, the noise spectra
derived from the classical description are essentially frequency-independent
and all quantum noise effects are absent. These effects are fully recovered
when charge is considered as a quantum degree of freedom.Comment: 12 pages; 3 figure
The puzzling interpretation of NIR indices: The case of NaI2.21
We present a detailed study of the Na I line strength index centered in the
-band at , {\AA} (NaI2.21 hereafter) relying on different samples of
early-type galaxies. Consistent with previous studies, we find that the
observed line strength indices cannot be fit by state-of-art scaled-solar
stellar population models, even using our newly developed models in the NIR.
The models clearly underestimate the large NaI2.21 values measured for most
early-type galaxies. However, we develop a Na-enhanced version of our newly
developed models in the NIR, which - together with the effect of a bottom-heavy
initial mass function - yield NaI2.21 indices in the range of the observations.
Therefore, we suggest a scenario in which the combined effect of [Na/Fe]
enhancement and a bottom-heavy initial mass function are mainly responsible for
the large NaI2.21 indices observed for most early-type galaxies. To a smaller
extent, also [C/Fe] enhancement might contribute to the large observed NaI2.21
values.Comment: 13 pages, 4 figures, accepted for publication in MNRA
Band alignment at metal/ferroelectric interfaces: insights and artifacts from first principles
Based on recent advances in first-principles theory, we develop a general
model of the band offset at metal/ferroelectric interfaces. We show that,
depending on the polarization of the film, a pathological regime might occur
where the metallic carriers populate the energy bands of the insulator, making
it metallic. As the most common approximations of density functional theory are
affected by a systematic underestimation of the fundamental band gap of
insulators, this scenario is likely to be an artifact of the simulation. We
provide a number of rigorous criteria, together with extensive practical
examples, to systematically identify this problematic situation in the
calculated electronic and structural properties of ferroelectric systems. We
discuss our findings in the context of earlier literature studies, where the
issues described in this work have often been overlooked. We also discuss
formal analogies to the physics of polarity compensation at LaAlO3/SrTiO3
interfaces, and suggest promising avenues for future research.Comment: 29 pages, 23 figure
Entanglement between charge qubits induced by a common dissipative environment
We study entanglement generation between two charge qubits due to the strong
coupling with a common bosonic environment (Ohmic bath). The coupling to the
boson bath is a source of both quantum noise (leading to decoherence) and an
indirect interaction between qubits. As a result, two effects compete as a
function of the coupling strength with the bath: entanglement generation and
charge localization induced by the bath. These two competing effects lead to a
non-monotonic behavior of the concurrence as a function of the coupling
strength with the bath. As an application, we present results for charge qubits
based on double quantum dots.Comment: 9 pages, 7 figure
Finite-frequency counting statistics of electron transport: Markovian Theory
We present a theory of frequency-dependent counting statistics of electron
transport through nanostructures within the framework of Markovian quantum
master equations. Our method allows the calculation of finite-frequency current
cumulants of arbitrary order, as we explicitly show for the second- and
third-order cumulants. Our formulae generalize previous zero-frequency
expressions in the literature and can be viewed as an extension of MacDonald's
formula beyond shot noise. When combined with an appropriate treatment of
tunneling, using, e.g. Liouvillian perturbation theory in Laplace space, our
method can deal with arbitrary bias voltages and frequencies, as we illustrate
with the paradigmatic example of transport through a single resonant level
model. We discuss various interesting limits, including the recovery of the
fluctuation-dissipation theorem near linear response, as well as some drawbacks
inherent of the Markovian description arising from the neglect of quantum
fluctuations.Comment: Accepted in New Journal of Physics. Updated tex
From Andreev to Majorana bound states in hybrid superconductor-semiconductor nanowires
Electronic excitations above the ground state must overcome an energy gap in
superconductors with spatially-homogeneous s-wave pairing. In contrast,
inhomogeneous superconductors such as those with magnetic impurities or weak
links, or heterojunctions containing normal metals or quantum dots, can host
subgap electronic excitations that are generically known as Andreev bound
states (ABSs). With the advent of topological superconductivity, a new kind of
ABS with exotic qualities, known as Majorana bound state (MBS), has been
discovered. We review the main properties of ABSs and MBSs, and the
state-of-the-art techniques for their detection. We focus on hybrid
superconductor-semiconductor nanowires, possibly coupled to quantum dots, as
one of the most flexible and promising experimental platforms. We discuss how
the combined effect of spin-orbit coupling and Zeeman field in these wires
triggers the transition from ABSs into MBSs. We show theoretical progress
beyond minimal models in understanding experiments, including the possibility
of different types of robust zero modes that may emerge without a
band-topological transition. We examine the role of spatial non-locality, a
special property of MBS wavefunctions that, together with non-Abelian braiding,
is the key to realizing topological quantum computation.Comment: Review. 23 pages, 8 figures, 1 table. Shareable published version by
Springer Nature at https://rdcu.be/b7DWT (free to read but not to download
Origin of the anomalies: the modified Heisenberg equation
The origin of the anomalies is analyzed. It is shown that they are due to the
fact that the generators of the symmetry do not leave invariant the domain of
definition of the Hamiltonian and then a term, normally forgotten in the
Heisenberg equation, gives an extra contribution responsible for the non
conservation of the charges. This explanation is equivalent to that of the
Fujikawa in the path integral formalism. Finally, this approach is applied to
the conformal symmetry breaking in two-dimensional quantum mechanics.Comment: 7 pages, LaTe
Current noise of a superconducting single electron transistor coupled to a resonator
We analyze the current and zero-frequency current noise properties of a
superconducting single electron resonator (SSET) coupled to a resonator,
focusing on the regime where the SSET is operated in the vicinity of the
Josephson quasiparticle resonance. We consider a range of coupling strengths
and resonator frequencies to reflect the fact that in practice the system can
be tuned to quite a high degree with the resonator formed either by a
nanomechanical oscillator or a superconducting stripline fabricated in close
proximity to the SSET. For very weak couplings the SSET acts on the resonator
like an effective thermal bath. In this regime the current characteristics of
the SSET are only weakly modified by the resonator. Using a mean field
approach, we show that the current noise is nevertheless very sensitive to the
correlations between the resonator and the SSET charge. For stronger couplings,
the SSET can drive the resonator into limit cycle states where self-sustained
oscillation occurs and we find that regions of well-defined bistability exist.
Dynamical transitions into and out of the limit cycle state are marked by
strong fluctuations in the resonator energy, but these fluctuations are
suppressed within the limit cycle state. We find that the current noise of the
SSET is strongly influenced by the fluctuations in the resonator energy and
hence should provide a useful indicator of the resonator's dynamics.Comment: Reduced quality figures for arXiv version; v2 minor correction
Charge qubit dynamics in a double quantum dot coupled to phonons
The dynamics of charge qubit in a double quantum dot coupled to phonons is
investigated theoretically in terms of a perturbation treatment based on a
unitary transformation. The dynamical tunneling current is obtained explicitly.
The result is compared with the standard perturbation theory at Born-Markov
approximation. The decoherence induced by acoustic phonons is analyzed at
length. It is shown that the contribution from deformation potential coupling
is comparable to that from piezoelectric coupling in small dot size and large
tunneling rate case. A possible decoupling mechanism is predicted.Comment: 8 pages, 6 figure
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