pinecone/core-2020-05-10-deduplication huggingface dataset:
Four-level systems and a universal quantum gate

We discuss a possibility of implementing a universal quantum XOR gate, by
using two coupled quantum dots subjected to external magnetic fields that are
parallel and slightly different. We consider this system in two different field
configurations. In the first case, parallel external fields with the intensity
difference at each spin being proportional to the time-dependent interaction
between the spins. General exact solution describing this system is presented
and analyzed to adjust parameters of the field. Then we consider parallel
fields with intensity difference at each spin being constant and the
interaction between the spins switching on and off adiabatically. In both cases
we adjust characteristics of the external fields (their intensities and
duration) in order to have the parallel pulse adequate for constructing the XOR
gate. In order to provide a complete theoretical description of all the cases,
we derive relations between the spin interaction, the inter-dot distance, and
the external field.Comment: 12 page
Nonlocal Special Relativity

DOI: 10.1002/andp.200810308In the special theory of relativity, Lorentz invariance is extended in Minkowski spacetime from ideal inertial observers to actual observers by means of the hypothesis of locality, which postulates that accelerated observers are always pointwise inertial. A critical examination of the locality assumption reveals its domain of validity: it is true for pointwise coincidences, but is in conflict with wave-particle duality. To remedy this situation, a nonlocal theory of accelerated systems is presented that reduces to the standard theory in the limit of small accelerations. Some of the main consequences of nonlocal special relativity are briefly outlined
Vacuum driven accelerated expansion

It has been shown that an improved estimation of quantum vacuum energy can
yield not only acceptable but also experimentally sensible results. The very
idea consists in a straightforward extraction of gravitationally interacting
part of the full quantum vacuum energy by means of gauge transformations. The
implementation of the idea has been performed in the formalism of effective
action, in the language of Schwinger's proper time and the Seeley-DeWitt heat
kernel expansion, in the background of the Friedmann-Robertson-Walker geometry.Comment: 11 pages, 2 figures, minor improvements, final preprint version,
  published version:
  http://www3.interscience.wiley.com/journal/120847180/abstract, devoted to the
  memory of professor Ryszard Raczka on the occasion of the 11th anniversary of
  his deat
Maxwell's equations in Minkowski's world: their premetric generalization and the electromagnetic energy-momentum tensor

http://www3.interscience.wiley.com/cgi-bin/fulltext/121382704/PDFSTARTIn December 1907, Minkowski expressed the Maxwell equations in the very beautiful and compact 4-dimensional form: lor f = −s, lor F∗ = 0. Here 'lor', an abbreviation of Lorentz, represents the 4-dimensional differential operator. We study Minkowski's derivation and show how these equations generalize to their modern premetric form in the framework of tensor and exterior calculus (valid also in general relativity). After mentioning some applications of premetric electrodynamics, we turn to Minkowski's discovery of the energy-momentum tensor of the electromagnetic field. We discuss how he arrived at it and how its premetric formulation looks like.At an earlier stage, this work was supported partly by the Deutsche Forschungsgemeinschaft (Bonn) with the grant HE 528/21-1
A Look at the Abandoned Contributions to Cosmology of Dirac, Sciama and
  Dicke

The separate contributions to cosmology of the above researchers are
revisited and a cosmology encompassing their basic ideas is proposed. We study
Dirac's article on the large number hypothesis (1938), Sciama's proposal of
realizing Mach's principle (1953), and Dicke's considerations (1957) on a
flat-space representation of general relativity with a variable speed of light
(VSL). Dicke's tentative theory can be formulated in a way which is compatible
with Sciama's hypothesis on the gravitational constant G. Additionally, such a
cosmological model is shown to satisfy Dirac's second `large number' hypothesis
on the total number of particles in the universe being proportional to the
square of the epoch. In the same context, Dirac's first hypothesis on an
epoch-dependent G-contrary to his prediction- does not necessarily produce a
visible time dependence of G. While Dicke's proposalreproduces the classical
tests of GR in first approximation, the cosmological redshift is described by a
shortening of measuring rods rather than an expansion of space. Since the
temporal evolution of the horizon R is governed by \dot R(t) =c(t), the
flatness and horizon problems do not arise in the common form.Comment: 15 pages LaTeX, v5: version (almost identical) accepted for
  publication in Annalen der Physi
Thermoballistic spin-polarized electron transport in paramagnetic
  semiconductors

Spin-polarized electron transport in diluted magnetic semiconductors (DMS) in
the paramagnetic phase is described within the thermoballistic transport model.
In this (semiclassical) model, the ballistic and diffusive transport mechanisms
are unified in terms of a thermoballistic current in which electrons move
ballistically across intervals enclosed between arbitrarily distributed points
of local thermal equilibrium. The contribution of each interval to the current
is governed by the momentum relaxation length. Spin relaxation is assumed to
take place during the ballistic electron motion. In paramagnetic DMS exposed to
an external magnetic field, the conduction band is spin-split due to the giant
Zeeman effect. In order to deal with this situation, we extend our previous
formulation of thermoballistic spin-polarized transport so as to take into
account an arbitrary (position-dependent) spin splitting of the conduction
band. The current and density spin polarizations as well as the
magnetoresistance are each obtained as the sum of an equilibrium term
determined by the spin-relaxed chemical potential, and an off-equilibrium
contribution expressed in terms of a spin transport function that is related to
the splitting of the spin-resolved chemical potentials. The procedures for the
calculation of the spin-relaxed chemical potential and of the spin transport
function are outlined. As an illustrative example, we apply the thermoballistic
description to spin-polarized transport in DMS/NMS/DMS heterostructures formed
of a nonmagnetic semiconducting sample (NMS) sandwiched between two DMS layers.
We evaluate the current spin polarization and the magnetoresistance for this
case and, in the limit of small momentum relaxation length, find our results to
agree with those of the standard drift-diffusion approch to electron transport.Comment: Minor corrections; 3 references added; changed to single-column
  forma
Improved analytical approximation to arbitrary l-state solutions of the
  Schrodinger equation for the hyperbolical potentials

A new approximation scheme to the centrifugal term is proposed to obtain the
$l\neq 0$ bound-state solutions of the Schr\"{o}dinger equation for an
exponential-type potential in the framework of the hypergeometric method. The
corresponding normalized wave functions are also found in terms of the Jacobi
polynomials. To show the accuracy of the new proposed approximation scheme, we
calculate the energy eigenvalues numerically for arbitrary quantum numbers $n$
and $l$ with two different values of the potential parameter
$\sigma_{\text{0}}.$ Our numerical results are of high accuracy like the other
numerical results obtained by using program based on a numerical integration
procedure for short-range and long-range potentials. The energy bound-state
solutions for the s-wave ($l=0$) and $\sigma_{0}=1$ cases are given.Comment: 17 page
Nonlinear Interactions of Gravitational Wave with Matter in
  Magnetic-type Maxwell-Vlasov Description

The interactions of gravitational waves with interstellar matter, dealing
with resonant wave-particle and wave-wave interactions, are considered on the
basis of magnetic-type Maxwell-Vlasov equations. It is found that the behavior
of the fields, involving the "gravitoelectromagnetic" or "GEM " fields, the
perturbed density field and self-generated gravitomagnetic field with low
frequency,can be described by the nonlinear coupling equations Eqs.
(6.10)-(6.12). Numerical results show that they may collapse. In other words,
due to self-condensing, a stronger GME fields could be produced; and they could
appear as the gravitational waves with high energy reaching on Earth. In this
case, Weber's results, perhaps, are acceptable.Comment: 13 figures, submit to Phys.Rev.
Intrinsic decoherence in the interaction of two fields with a two-level
  atom

We study the interaction of a two-level atom and two fields, one of them
classical. We obtain an effective Hamiltonian for this system by using a method
recently introduced that produces a small rotation to the Hamiltonian that
allows to neglect some terms in the rotated Hamiltonian. Then we solve a
variation of the Schr\"odinger equation that models decoherence as the system
evolves through intrinsic mechanisms beyond conventional quantum mechanics
rather than dissipative interaction with an environment
(0,2) Gauged Linear Sigma Model on Supermanifold

We construct (0,2), D=2 gauged linear sigma model on a supermanifold in both
the Abelian gauge group and the non-Abelian gauge group. The $\hat{U}$ operator
provides consistency conditions for satisfying the SUSY invariance. Contrary to
the Abelian gauge group, it is not essential to introduce the new operator in
order to check the exact SUSY invariance of the Lagrangian density. However, in
order to introduce the (0,2) chiral superfields, we need the $\hat{U}$
operator, because we can not define the (0,2) chirality conditions of the (0,2)
chiral superfields without introducing the new operator by using $\hat{U}$ and
the enlarged operator \hat{U}^{a} was obtained from the conditions that yield
the (0,2) supersymmetric invariance of the Lagrangian density of the (0,2) U(N)
gauged linear sigma model in superfield formalism. We found that the
consistency conditions for the Abelian gauge group which assure the (0,2)
supersymmetric invariance of Lagrangian density agree with (0,2) chirality
conditions for superpotential. The supermanifold \mathcal{M}^{m|n} becomes the
super weighted complex projective space WCP^{m-1|n} in U(1) case, which is
considered as an example of Calabi-Yau supermanifold.Comment: 19 pages, no figures, Verification of component fields are delete
Reply to Itin, Obukhov and Hehl paper "An Electric Charge has no Screw
  Sense - A Comment on the Twist-Free Formulation of Electrodynamics by da
  Rocha & Rodrigues"

In this note we briefly comment a paper by Itin, Obukhov and Hehl criticising
our previous paper. We show that all remarks by our critics are ill conceived
or irrelevant to our approach and moreover we provide some pertinent new
comments to their critical paper, with the aim to clarify even more our view on
the subject.Comment: This paper is a reply to arXiv:0911.5175 [physics.class-ph] which
  made some criticisms on our paper "Pair and Impar, Even and Odd Form Fields
  and Electromagnetism" arXiv:0811.1713 [math-ph] to appear in Annalen der
  Physik. A short version of our reply will also appear in Annalen de Physi
Ageing in granular aluminium insulating thin films

We present a new set of electrical field effect measurements on granular
aluminium insulating thin films. We have explored how the conductance
relaxations induced by gate voltage changes depend on the age of the system,
namely the time elapsed since its quench at low temperature. A clear age
dependence of the relaxations is seen, qualitatively similar to ageing effects
seen in other well studied glassy systems such as spin glasses or polymers. We
explain how our results differ from the previous ones obtained with different
protocols in indium oxide and granular aluminium thin films. Our experimental
findings bring new information on the dynamics of the system and put new
constraints on the theoretical models that may explain slow conductance
relaxations in disordered insulators.Comment: 4 pages, 13th Transport in interacting disordered systems (TIDS13)
  conference, 31.08.2009 - 05.09.2009, Rackeve, Hungar
Magnetoresistance in Dilute $p$-Si/SiGe in Parallel and Tilted Magnetic
  Fields

We report the results of an experimental study of the magnetoresistance
$\rho_{xx}$ and $\rho_{xy}$ in two samples of $p$-Si/SiGe with low carrier
concentrations $p$=8.2$\times10^{10}$ cm$^{-2}$ and $p$=2$\times10^{11}$
cm$^{-2}$. The research was performed in the temperature range of 0.3-2 K and
in the magnetic fields of up to 18 T, parallel or tilted with respect to the
two-dimensional (2D) channel plane. The large in-plane magnetoresistance can be
explained by the influence of the \textit{in-plane} magnetic field on the
orbital motion of the charge carriers in the quasi-2D system. The measurements
of $\rho_{xx}$ and $\rho_{xy}$ in the tilted magnetic field showed that the
anomaly in $\rho_{xx}$, observed at filling factor $\nu$=3/2 is practically
nonexistent in the conductivity $\sigma_{xx}$. The anomaly in $\sigma_{xx}$ at
$\nu$=2 might be explained by overlapping of the levels with different spins
0$\uparrow$ and 1$\downarrow$ when the tilt angle of the applied magnetic field
is changed. The dependence of g-factor $g^*(\Theta)/g^*(0^0)$ on the tilt angle
$\Theta$ was determined.Comment: 4 pages, 6 figs, to appear in Annalen der Physi
Localised Magneto-Optical Collective Excitations of Impure Graphene

We study optically-induced collective excitations of graphene in the presence
of a strong perpendicular magnetic field and a single impurity. We determine
the energies and absorption strengths of these excitations, which become
localised on the impurity. Two different types of impurity are considered i.
the long-range Coulomb impurity, ii. a delta-function impurity located at
either an A or B graphene sublattice site. Both impurity types result in some
bound states appearing both above and below the magnetoplasmon continuum,
although the effect of the short-range impurity is less pronounced. The
dependence of the energies and oscillator strengths of the bound states on the
filling factor is investigated.Comment: 4 pages, 4 figures, accepted for publication in Ann. Phys. (Leipzig
1/f noise and slow relaxations in glasses

Recently we have shown that slow relaxations in the electron glass system can
be understood in terms of the spectrum of a matrix describing the relaxation of
the system close to a metastable state. The model focused on the electron glass
system, but its generality was demonstrated on various other examples. Here, we
study the noise spectrum in the same framework. We obtain a remarkable relation
between the spectrum of relaxation rates $\lambda$ described by the
distribution function $P(\lambda) \sim 1/\lambda$ and the $1/f$ noise in the
fluctuating occupancies of the localized electronic sites. This noise can be
observed using local capacitance measurements. We confirm our analytic results
using numerics, and also show how the Onsager symmetry is fulfilled in the
system
Transport through a Kondo quantum dot: Functional RG approach

We apply the functional renormalization group (FRG) method to calculate the
conductance of a quantum dot in the Kondo regime. Starting from the exact FRG
equations in Keldysh formulation for the Kondo exchange Hamiltonian in
pseudo-fermion (pf) representation, we solve the coupled equations for the pf
self energy and the coupling function, neglecting three-particle and higher
correlation functions. The conductance $G$ as a function of temperature $T$ and
bias voltage $V$ is calculated using a renormalized Golden Rule expression. The
limiting behavior at $T$ and/or $V$ $\gg T_{K}$ ($T_{K}$ : Kondo temperature)
agrees with known results. The difficulties when approaching strong coupling
are analyzed and improvements are suggested.Comment: accepted for publication in Ann. Phys. (Berlin
An electric charge has no screw sense--a comment on the twistfree
  formulation of electrodynamics by da Rocha & Rodrigues

Da Rocha and Rodigues (RR) claim (i) that in classical electrodynamics in
vector calculus the distinction between polar and axial vectors and in exterior
calculus between twisted and untwisted forms is inappropriate and superfluous,
and (ii) that they can derive the Lorentz force equation from Maxwell's
equations. As to (i), we point out that the distinction of polar/axial and
twisted/untwisted derives from the property of the electric charge of being a
pure scalar, that is, not carrying any screw sense. Therefore, the mentioned
distinctions are necessary ingredients in any fundamental theory of
electrodynamics. If one restricted the allowed coordinate transformations to
those with positive Jacobian determinants (or prescribed an equivalent
constraint), then the RR scheme could be accommodated; however, such a
restriction is illegal since electrodynamics is, in fact, also covariant under
transformations with negative Jacobians. As to (ii), the "derivation" of the
Lorentz force from Maxwell's equations, we point out that RR forgot to give the
symbol F (the field strength) in Maxwell's equations an operational meaning in
the first place. Thus, their proof is empty. Summing up: the approach of RR
does not bring in any new insight into the structure of electrodynamics.Comment: Added answer to da Rocha & Rodrigues arXiv:0912.212
Electrodynamics in accelerated frames revisited

Maxwell's equations are formulated in arbitrary moving frames by means of
tetrad fields, which are interpreted as reference frames adapted to observers
in space-time. We assume the existence of a general distribution of charges and
currents in an inertial frame. Tetrad fields are used to project the
electromagnetic fields and sources on accelerated frames. The purpose is to
study several configurations of fields and observers that in the literature are
understood as paradoxes. For instance, are the two situations, (i) an
accelerated charge in an inertial frame, and (ii) a charge at rest in an
inertial frame described from the perspective of an accelerated frame,
physically equivalent? Is the electromagnetic radiation the same in both
frames? Normally in the analysis of these paradoxes the electromagnetic fields
are transformed to (uniformly) accelerated frames by means of a coordinate
transformation of the Faraday tensor. In the present approach coordinate and
frame transformations are disentangled, and the electromagnetic field in the
accelerated frame is obtained through a frame (local Lorentz) transformation.
Consequently the fields in the inertial and accelerated frames are described in
the same coordinate system. This feature allows the investigation of paradoxes
such as the one mentioned above.Comment: 17 pages, no figure
Viscous Quark-Gluon Plasma in the Early Universe

We consider the evolution of a flat, isotropic and homogeneous
Friedmann-Robertson-Walker Universe, filled with a causal bulk viscous
cosmological fluid, that can be characterized by an ultra-relativistic equation
of state and bulk viscosity coefficient obtained from recent lattice QCD
calculations. The basic equation for the Hubble parameter is derived under the
assumption that the total energy in the Universe is conserved. By assuming a
power law dependence of bulk viscosity coefficient, temperature and relaxation
time on energy density, an approximate solution of the field equations has been
obtained, in which we utilized equations of state from recent lattice QCD
simulations QCD and heavy-ion collisions to derive an evolution equation. In
this treatment for the viscous cosmology, we found no evidence for singularity.
For example, both Hubble parameter and scale factor are finite at $t=0$, $t$ is
the comoving time. Furthermore, their time evolution essentially differs from
the one associated with non-viscous and ideal gas. Also thermodynamic
quantities, like temperature, energy density and bulk pressure remain finite as
well. In order to prove that the free parameter in our model does influence the
final results, qualitatively, we checked out other articular solutions.Comment: 19 pages, 4 figures including 7 eps graph
Bulk and Shear Viscosity in Hagedorn Fluid

Assuming that the Hagedorn fluid composed of known particles and resonances
with masses $m<2\,$GeV obeys the {\it first-order} theory (Eckart) of
relativistic fluid, we discuss the transport properties of QCD confined phase.
Based on the relativistic kinetic theory formulated under the relaxation time
approximation, expressions for bulk and shear viscosity in thermal medium are
derived. The relaxation time in the Hagedorn dynamical fluid exclusively takes
into account the decay and eventually van der Waals processes. We comment on
the {\it in-medium} thermal effects on bulk and shear viscosities and averaged
relaxation time with and without the excluded-volume approach. As an
application of these results, we suggest the dynamics of heavy-ion collisions,
non-equlibrium thermodynamics and the cosmological models, which require thermo
and hydrodynamics equations of state.Comment: 6 Pages, 5 figures with 5 eps graph
A Categorical Framework for Quantum Theory

Underlying any theory of physics is a layer of conceptual frames. They
connect the mathematical structures used in theoretical models with physical
phenomena, but they also constitute our fundamental assumptions about reality.
Many of the discrepancies between quantum physics and classical physics
(including Maxwell's electrodynamics and relativity) can be traced back to
these categorical foundations. We argue that classical physics corresponds to
the factual aspects of reality and requires a categorical framework which
consists of four interdependent components: boolean logic, the
linear-sequential notion of time, the principle of sufficient reason, and the
dichotomy between observer and observed. None of these can be dropped without
affecting the others. However, in quantum theory the reduction postulate also
addresses the "status nascendi" of facts, i.e., their coming into being.
Therefore, quantum phyics requires a different conceptual framework which will
be elaborated in this article. It is shown that many of its components are
already present in the standard formalisms of quantum physics, but in most
cases they are highlighted not so much from a conceptual perspective but more
from their mathematical structures. The categorical frame underlying quantum
physics includes a profoundly different notion of time which encompasses a
crucial role for the present.Comment: 35 pages, 1 figur
Modification of black-body radiance at low temperatures and frequencies

In contrast to earlier reports, where the spectrum of the {\sl energy
density} of photonic black-body radiation modified by SU(2) effects was
discussed, we discuss the low-frequency spectrum of the {\sl radiance} at
temperatures ranging between 5 and 20 Kelvin. We conclude that compared to the
conventional theory the only observable effect is associated with the spectral
gap (total screening). We also discuss how a low-temperature black body cavity
under the influence of a sufficiently strong static electric field is forced to
emit according to Planck's radiation law (pure U(1) theory) even at low
frequencies and how this effect can be utilized to measure SU(2) induced
deviations.Comment: 10 pp, 5 figs; v2: slight changes in text, extended discussion of
  Rydberg-atom experimen