pinecone/core-2020-05-10-deduplication huggingface dataset:
Cloaks, editors, and bubbles: applications of spacetime transformation
  theory

Spacetime or `event' cloaking was recently introduced as a concept, and the
theoretical design for such a cloak was presented for illumination by
electromagnetic waves [McCall, Favaro, Kinsler, Boardman 2011]. Here we
describe how event cloaks can be designed for simple wave systems, using either
an approximate `speed cloak' method, or an exact full-wave one. Further, we
discuss in detail many of the implications of spacetime transformation devices,
covering their (usually) directional nature, spacetime distortions (as opposed
to cloaks), and how leaky cloaks manifest themselves. We also address more
exotic concepts that follow naturally on from considerations of simple
spacetime transformation devices, such as spacetime modeling and causality
editors; and describe a proposal for implementing the
interrupt-without-interrupt concept suggested by McCall et al. We also describe
how we might make a simple time-dependent `bubbleverse' by embedding a
modulated Maxwell's Fisheye transformation device (T-device) in a flat
background spacetime.Comment: 11 pages, 12 figures (v2 - update fig 6, 7) (v3 - closer to published
  version) Previously titled "Some thoughts on spacetime transformation theory
Master equation approach to conductivity of bosonic and fermionic
  carriers in one- and two-dimensional lattices

We discuss the master equation approach to diffusive current of bosonic or
fermionic carriers in one- and two-dimensional lattices. This approach is shown
to reproduce all known results of the linear response theory, including the
integer quantum Hall effect for fermionic carriers. The main advantage of the
approach is that it allows to calculate the current beyond the linear response
regime where new effects are found. In particular, we show that the Hall
current can be inverted by changing orientation of the static force (electric
field) relative to the primary axes of the lattice.Comment: 22 pages, 9 figure
Electron quantum optics in ballistic chiral conductors

The edge channels of the quantum Hall effect provide one dimensional chiral
and ballistic wires along which electrons can be guided in optics like setup.
Electronic propagation can then be analyzed using concepts and tools derived
from optics. After a brief review of electron optics experiments performed
using stationary current sources which continuously emit electrons in the
conductor, this paper focuses on triggered sources, which can generate
on-demand a single particle state. It first outlines the electron optics
formalism and its analogies and differences with photon optics and then turns
to the presentation of single electron emitters and their characterization
through the measurements of the average electrical current and its
correlations. This is followed by a discussion of electron quantum optics
experiments in the Hanbury-Brown and Twiss geometry where two-particle
interferences occur. Finally, Coulomb interactions effects and their influence
on single electron states are considered
N=2 supersymmetric radiation damping problem on a noncommutative plane

It is well known that a direct Lagrangian description of radiation damping is
still missing. In this paper a specific approach of this problem was used,
which is the standard way to treat the radiation damping problem. A $N=2$
supersymmetric extension for the model describing the radiation damping on the
noncommutative plane with electric and magnetic interactions was obtained. The
entire supercharge algebra and the total Hamiltonian for the system were
analyzed. Finally, noncommutativity features were introduced and its
consequences were explored..Comment: 13 pages. In memory of prof. Wilson Oliveira. arXiv admin note: text
  overlap with arXiv:1307.731
The quest for axions and other new light particles

Standard Model extensions often predict low-mass and very weakly interacting
particles, such as the axion. A number of small-scale experiments at the
intensity/precision frontier are actively searching for these elusive
particles, complementing searches for physics beyond the Standard Model at
colliders. Whilst a next generation of experiments will give access to a huge
unexplored parameter space, a discovery would have a tremendous impact on our
understanding of fundamental physics.Comment: Developed from a contribution to the Open Symposium of the European
  Strategy Preparatory Group, 10-12 September 2012, Krakow; 9 pages, 3 figure
Excitation of radial collective modes in a quantum dot: Beyond linear
  response

We compare the response of five different models of two interacting electrons
in a quantum dot to an external short lived radial excitation that is strong
enough to excite the system well beyond the linear response regime. The models
considered describe the Coulomb interaction between the electrons in different
ways ranging from mean-field approaches to configuration interaction (CI)
models, where the two-electron Hamiltonian is diagonalized in a large truncated
Fock space. The radially symmetric excitation is selected in order to severely
put to test the different approaches to describe the interaction and
correlations of an electron system in a nonequilibrium state. As can be
expected for the case of only two electrons none of the mean-field models can
in full details reproduce the results obtained by the CI model. Nonetheless,
some linear and nonlinear characteristics are reproduced reasonably well. All
the models show activation of an increasing number of collective modes as the
strength of the excitation is increased. By varying slightly the confinement
potential of the dot we observe how sensitive the properties of the excitation
spectrum are to the Coulomb interaction and its correlation effects. In order
to approach closer the question of nonlinearity we solve one of the mean-field
models directly in a nonlinear fashion without resorting to iterations.Comment: PDFLaTeX, RevTeX, 12 pages with 16 included pdf figures. Scales in
  Fig. 10(b) and 12(b) repaired, minor spelling mistakes corrected, and the
  conclusion section extende
Curvature dark energy reconstruction through different cosmographic
  distance definitions

In the context of $f(\mathcal{R})$ gravity, dark energy is a geometrical
fluid with negative equation of state. Since the function $f(\mathcal{R})$ is
not known \emph{a priori}, the need of a model independent reconstruction of
its shape represents a relevant technique to determine which $f(\mathcal{R})$
model is really favored with respect to others. To this aim, we relate
cosmography to a generic $f(\mathcal R)$ and its derivatives in order to
provide a model independent investigation at redshift $z \sim 0$. Our analysis
is based on the use of three different cosmological distance definitions, in
order to alleviate the duality problem, i.e. the problem of which cosmological
distance to use with specific cosmic data sets. We therefore consider the
luminosity, $d_L$, flux, $d_F$, and angular, $d_A$, distances and we find
numerical constraints by the Union 2.1 supernovae compilation and measurement
of baryonic acoustic oscillations, at $z_{BAO}=0.35$. We notice that all
distances reduce to the same expression, i.e. $d_{L;F;A}\sim\frac{1}{\mathcal
H_0}z$, at first order. Thus, to fix the cosmographic series of observables, we
impose the initial value of $H_0$ by fitting $\mathcal H_0$ through supernovae
only, in the redshift regime $z<0.4$. We find that the pressure of curvature
dark energy fluid is slightly lower than the one related to the cosmological
constant. This indicates that a possible evolving curvature dark energy
realistically fills the current universe. Moreover, the combined use of
$d_L,d_F$ and $d_A$ shows that the sign of the acceleration parameter agrees
with theoretical bounds, while its variation, namely the jerk parameter, is
compatible with $j_0>1$. Finally, we infer the functional form of
$f(\mathcal{R})$ by means of a truncated polynomial approximation, in terms of
fourth order scale factor $a(t)$.Comment: 10 pages, 4 figures, to appear in Annalen der Physi
Constraining chameleon models with cosmology

Chameleon fields may modify gravity on cluster scales while recovering
general relativity locally. This article reviews signatures of chameleon
modifications in the nonlinear cosmological structure, comparing different
techniques to model them, summarising the current state of observational
constraints, and concluding with an outlook on prospective constraints from
future observations and applications of the analytic tools developed in the
process to more general scalar-tensor theories. Particular focus is given to
the Hu-Sawicki and designer models of f(R) gravity.Comment: 24 pages, 5 figures, 1 table; invited review article; v2 matches
  published versio
Re-Examining Astrophysical Constraints on the Dark Matter Model

Recent high-resolution simulations that include Cold Dark Matter (CDM) and
baryons have shown that baryonic physics can dramatically alter the dark matter
structure of galaxies. These results modify our predictions for observed galaxy
evolution and structure. Given these updated expectations, it is timely to
re-examine observational constraints on the dark matter model. A few
observations are reviewed that may indirectly trace dark matter, and may help
confirm or deny possible dark matter models. Warm Dark Matter (WDM) and
Self-Interacting Dark Matter (SIDM) are currently the favorite alternative
models to CDM. Constraints on the WDM particle mass require it to be so heavy
that WDM is nearly indistinguishable from CDM. The best observational test of
SIDM is likely to be in the dark matter distribution of faint dwarf galaxies,
but there is a lack of theoretical predictions for galaxy structure in SIDM
that account for the role of baryons.Comment: Invited review article (10 pages), accepted for publication in
  Annalen der Physik. This version has been modified slightly from the refereed
  version, including recent updates. The one figure has been compresse
Formation and diffusion characteristics of Pt clusters on graphene, 1H-MoS2 and 1T-TaS2

Many experiments have revealed that the surfaces of graphene and graphene-like structures can play an active role as a host surface for clusterization of transition metal atoms. Motivated by these observations, we investigate theoretically the adsorption, diffusion and magnetic properties of Pt clusters on three different two-dimensional atomic crystals using first principles density functional theory. We found that monolayers of graphene, molybdenum disulfide (1H-MoS2) and tantalum disulfide (1T-TaS2) provide different nucleation characteristics for Pt cluster formation. At low temperatures, while the bridge site is the most favorable site where the growth of a Pt cluster starts on graphene, top-Mo and top-Ta sites are preferred on 1H-MoS2 and 1T-TaS2, respectively. Ground state structures and magnetic properties of Ptn clusters (n = 2,3,4) on three different monolayer crystal structures are obtained. We found that the formation of Pt2 dimer and a triangle-shaped Pt3 cluster perpendicular to the surface are favored over the three different surfaces. While bent rhombus shaped Pt4 is formed on graphene, the formation of tetrahedral shaped clusters are more favorable on 1H-MoS2 and 1T-TaS2. Our study of the formation of Ptn clusters on three different monolayers provides a gateway for further exploration of nanocluster formations on various surfaces.Flemish Science Foundation (FWO-Vl); Methusalem foundation of the Flemish government; FWO Pegasus Long Marie Curie Fellowshi
Electronic Instabilities of the AA-Honeycomb Bilayer

We use a functional renormalization group approach to study the instabilities
due to electron-electron interactions in a bilayer honeycomb lattice model with
AA stacking, as it might be relevant for layered graphene with this structure.
Starting with a tight- binding description for the four $\pi$-bands, we
integrate out the modes of the dispersion by successively lowering an infrared
cutoff and determine the leading tendencies in the effective interactions. The
antiferromagnetic spin-density wave is an expected instability for dominant
local repulsion among the electrons, but for nonlocal interaction terms also
other instabilities occur. We discuss the phase diagrams depending on the model
parameters. We compare our results to single-layer graphene and the more common
AB-stacked bilayer, both qualitatively and quantitatively.Comment: 9 pages, 3 figures, Annalen der Physik, online available (2014
Generating the Schrodinger cat state in a nanomechanical resonator
  coupled to a charge qubit

We propose a scheme for generating the Schr\"{o}dinger cat state based on
geometric operations by a nanomechanical resonator coupled to a superconducting
charge qubit. The charge qubit, driven by two strong classical fields,
interacts with a high-frequency phonon mode of the nanomechanical resonator.
During the operation, the charge qubit undergoes no real transitions, while the
phonon mode of the nanomechanical resonator is displaced along different paths
in the phase space, dependent on the states of the charge qubit, which yields
the Schr\"{o}dinger cat state. The robustness of the scheme is justified by
considering noise from environment, and the feasibility of the scheme is
discussed.Comment: 6 pages 3 figure
Band Gaps and Optical Spectra from Single- and Double-Layer
  Fluorographene to Graphite Fluoride: Many-Body Effects and Excitonic States

We compare first-principle band gaps and optical absorption spectra of
single- and double-layer fluorographene with bulk graphite fluoride. The
electronic properties are calculated using the many-body GW approximation and
the optical spectra using the Bethe-Salpeter equation (BSE). The inclusion of
electron-hole interactions is crucial for predicting low energy excitonic
absorption peaks. The position of the first exciton peak is identical in
single-, double- and multilayer fluorographene, which may indicate that the
onset of the absorption spectra does not differ in these materials
Trajectories without quantum uncertainties

A common knowledge suggests that trajectories of particles in quantum
mechanics always have quantum uncertainties. These quantum uncertainties set by
the Heisenberg uncertainty principle limit precision of measurements of fields
and forces, and ultimately give rise to the standard quantum limit in
metrology. With the rapid developments of sensitivity of measurements these
limits have been approached in various types of measurements including
measurements of fields and acceleration. Here we show that a quantum trajectory
of one system measured relatively to the other "reference system" with an
effective negative mass can be quantum uncertainty--free. The method crucially
relies on the generation of an Einstein-Podolsky-Rosen entangled state of two
objects, one of which has an effective negative mass. From a practical
perspective these ideas open the way towards force and acceleration
measurements at new levels of sensitivity far below the standard quantum limit.Comment: Submitted to the special issue "Quantum and Hybrid Mechanical Systems
  - From Fundamentals to Applications" in Annalen der Physi
Entangling two distant non-interacting microwave modes

We propose a protocol able to prepare two remote and initially uncorrelated
microwave modes in an entangled stationary state, which is certifiable using
only local optical homodyne measurements. The protocol is an extension of
continuous variable entanglement swapping, and exploits two hybrid
quadripartite opto-electro-mechanical systems in which a nanomechanical
resonator acts as a quantum interface able to entangle optical and microwave
fields. The proposed protocol allows to circumvent the problems associated with
the fragility of microwave photons with respect to thermal noise and may
represent a fundamental tool for the realization of quantum networks connecting
distant solid-state and superconducting qubits, which are typically manipulated
with microwave fields. The certifying measurements on the optical modes
guarantee the success of entanglement swapping without the need of performing
explicit measurements on the distant microwave fields.Comment: 7 pages, 3 figures; to appear in the special issue "Quantum and
  Hybrid Mechanical Systems - From Fundamentals to Applications" in Annalen der
  Physi
Dicke-type phase transition in a multimode optomechanical system

We consider the "membrane in the middle" optomechanical model consisting of a
laser pumped cavity which is divided in two by a flexible membrane that is
partially transmissive to light and subject to radiation pressure. Steady state
solutions at the mean-field level reveal that there is a critical strength of
the light-membrane coupling above which there is a symmetry breaking
bifurcation where the membrane spontaneously acquires a displacement either to
the left or the right. This bifurcation bears many of the signatures of a
second order phase transition and we compare and contrast it with that found in
the Dicke model. In particular, by studying limiting cases and deriving
dynamical critical exponents using the fidelity susceptibility method, we argue
that the two models share very similar critical behaviour. For example, the
obtained critical exponents indicate that they fall within the same
universality class. Away from the critical regime we identify, however, some
discrepancies between the two models. Our results are discussed in terms of
experimentally relevant parameters and we evaluate the prospects for realizing
Dicke-type physics in these systems.Comment: 14 pages, 6 figure
Optoelectromechanical transducer: reversible conversion between
  microwave and optical photons

Quantum states encoded in microwave photons or qubits can be effectively
manipulated, whereas optical photons can be coherently transferred via optical
fibre and waveguide. The reversible conversion of quantum states between
microwave and optical photons will hence enable the distribution of quantum
information over long distance and significantly improve the scalability of
hybrid quantum systems. Owning to technological advances, mechanical resonators
couple to quantum devices in distinctly different spectral range with tunable
coupling, and can serve as a powerful interface to connect those devices. In
this review, we summarize recent theory and experimental progress in the
coherent conversion between microwave and optical fields via
optoelectromechanical transducers. The challenges and perspectives in achieving
single-photon-level quantum state conversion will also be discussed.Comment: Review article, to appear in Annalen der Physik; 7 figure
Massless Dirac cones in graphene: experiments and theory

The opening of a gap in single-layer graphene is often ascribed to the
breaking of the equivalence between the two carbon sublattices. We show by
angle-resolved photoemission spectroscopy that Ir- and Na-modified graphene
grown on the Ir(111) surface presents a very large unconventional gap that can
be described in terms of a phenomenological "massless" Dirac model. We discuss
the consequences and differences of this model in comparison of the standard
massive gap model, and we investigate the conditions under which such anomalous
gap can arise from a spontaneous symmetry breaking.Comment: 3 eps figures include
Towards Optomechanical Quantum State Reconstruction of Mechanical Motion

Utilizing the tools of quantum optics to prepare and manipulate quantum
states of motion of a mechanical resonator is currently one of the most
promising routes to explore non-classicality at a macroscopic scale. An
important quantum optomechanical tool yet to be experimentally demonstrated is
the ability to perform complete quantum state reconstruction. Here, after
providing a brief introduction to quantum states in phase space, we review and
contrast the current proposals for state reconstruction of mechanical motional
states and discuss experimental progress. Furthermore, we show that mechanical
quadrature tomography using back-action-evading interactions gives an
$s$-parameterized Wigner function where the numerical parameter $s$ is directly
related to the optomechanical measurement strength. We also discuss the effects
of classical noise in the optical probe for both state reconstruction and state
preparation by measurement.Comment: Published in the Annalen der Physik special issue: Quantum and Hybrid
  Mechanical Systems edited by Harris, Rabl, and Schliesser (11 pages, 2
  figures, close to published version
Transient dynamics of an adiabatic NEMS

This paper is focused on the transient dynamics of an adiabatic
nano-electromechanical system (NEMS), consisting of a nano-mechanical
oscillator coupled to a quantum dot. By numerically solving the nonlinear
stochastic differential equation governing the oscillator, the time evolution
of the oscillator position, of the dot occupation number and of the current are
studied. Different parameter settings are studied where the system exhibits
bi-stable, tri-stable or mono-stable behavior on a finite-time horizon. It is
shown that, after a typically long transient, the system under investigation
exhibits no hysteretic behavior and that a unique steady state is reached,
independently of the initial conditions. The transient dynamics is marked out
by one or two well separated characteristic times, depending on the considered
case (i.e., mono- or multi-stable). We evaluate these times for a dot
on-resonance or off-resonance. It turns out that the characteristic time scales
are long in comparison to the period of the uncoupled oscillator, particularly
at low bias, suggesting that the predicted transient dynamics may be observed
in state-of-the-art experimental setups.Comment: 14 pages, 10 color figure
From membrane-in-the-middle to mirror-in-the-middle with a
  high-reflectivity sub-wavelength grating

We demonstrate a "membrane in the middle" optomechanical system using a
silicon nitride membrane patterned as a subwavelength grating. The grating has
a reflectivity of over 99.8%, effectively creating two sub-cavities, with free
spectral ranges of 6 GHz, optically coupled via photon tunneling. Measurements
of the transmission and reflection spectra show an avoided crossing where the
two sub-cavities simultaneously come into resonance, with a frequency splitting
of 54 MHz. We derive expressions for the lineshapes of the symmetric and
antisymmetric modes at the avoided crossing, and infer the grating reflection,
transmission, absorption, and scattering through comparison with the
experimental data.Comment: 7 pages, 4 figure
Quantum synchronization of two Van der Pol oscillators

We study synchronization of two dissipatively coupled Van der Pol oscillators
in the quantum regime. Due to quantum noise strict frequency locking is absent
and is replaced by a crossover from weak to strong frequency entrainment. We
discuss the differences to the behavior of one quantum Van der Pol oscillator
subject to an external drive. Moreover, we describe a possible experimental
realization of two coupled quantum van der Pol oscillators in an optomechanical
setting.Comment: 8 pages, 5 figures, submitted to the topical issue "Quantum and
  Hybrid Mechanical Systems" in Annalen der Physi