3,130 research outputs found
Broken-symmetry-adapted Green function theory of condensed matter systems:towards a vector spin-density-functional theory
The group theory framework developed by Fukutome for a systematic analysis of
the various broken symmetry types of Hartree-Fock solutions exhibiting spin
structures is here extended to the general many body context using spinor-Green
function formalism for describing magnetic systems. Consequences of this theory
are discussed for examining the magnetism of itinerant electrons in nanometric
systems of current interest as well as bulk systems where a vector spin-density
form is required, by specializing our work to spin-density-functional
formalism. We also formulate the linear response theory for such a system and
compare and contrast them with the recent results obtained for localized
electron systems. The various phenomenological treatments of itinerant magnetic
systems are here unified in this group-theoretical description.Comment: 17 page
Joint measurability, steering and entropic uncertainty
The notion of incompatibility of measurements in quantum theory is in stark
contrast with the corresponding classical perspective, where all physical
observables are jointly measurable. It is of interest to examine if the results
of two or more measurements in the quantum scenario can be perceived from a
classical point of view or they still exhibit non-classical features. Clearly,
commuting observables can be measured jointly using projective measurements and
their statistical outcomes can be discerned classically. However, such simple
minded association of compatibility of measurements with commutativity turns
out to be limited in an extended framework, where the usual notion of sharp
projective valued measurements of self adjoint observables gets broadened to
include unsharp measurements of generalized observables constituting positive
operator valued measures (POVM). There is a surge of research activity recently
towards gaining new physical insights on the emergence of classical behavior
via joint measurability of unsharp observables. Here, we explore the entropic
uncertainty relation for a pair of discrete observables (of Alice's system)
when an entangled quantum memory of Bob is restricted to record outcomes of
jointly measurable POVMs only. Within the joint measurability regime, the sum
of entropies associated with Alice's measurement outcomes - conditioned by the
results registered at Bob's end - are constrained to obey an entropic steering
inequality. In this case, Bob's non-steerability reflects itself as his
inability in predicting the outcomes of Alice's pair of non-commuting
observables with better precision, even when they share an entangled state. As
a further consequence, the quantum advantage envisaged for the construction of
security proofs in key distribution is lost, when Bob's measurements are
restricted to the joint measurability regime.Comment: 5 pages, RevTeX, 1 pdf figure, Comments welcom
Development of three dimensional constitutive theories based on lower dimensional experimental data
Most three dimensional constitutive relations that have been developed to
describe the behavior of bodies are correlated against one dimensional and two
dimensional experiments. What is usually lost sight of is the fact that
infinity of such three dimensional models may be able to explain these
experiments that are lower dimensional. Recently, the notion of maximization of
the rate of entropy production has been used to obtain constitutive relations
based on the choice of the stored energy and rate of entropy production, etc.
In this paper we show different choices for the manner in which the body stores
energy and dissipates energy and satisfies the requirement of maximization of
the rate of entropy production that leads to many three dimensional models. All
of these models, in one dimension, reduce to the model proposed by Burgers to
describe the viscoelastic behavior of bodies.Comment: 23 pages, 6 figure
Bulk viscosity of spin-one color superconducting strange quark matter
The bulk viscosity in spin-one color-superconducting strange quark matter is
calculated by taking into account the interplay between the nonleptonic and
semi-leptonic week processes. In agreement with previous studies, it is found
that the inclusion of the semi-leptonic processes may result in non-negligible
corrections to the bulk viscosity in a narrow window of temperatures. The
effect is generally more pronounced for pulsars with longer periods. Compared
to the normal phase, however, this effect due to the semi-leptonic processes is
less pronounced in spin-one color superconductors. Assuming that the critical
temperature of the phase transition is much larger than 40 keV, the main effect
of spin-one color superconductivity in a wide range of temperatures is an
overall increase of the bulk viscosity with respect to the normal phase. The
corresponding enhancement factor reaches up to about 9 in the polar and
A-phases, about 25 in the planar phase and about 29 in the CSL phase. This
factor is determined by the suppression of the nonleptonic rate in
color-superconducting matter and, therefore, may be even larger if all quark
quasiparticles happen to be gapped.Comment: 10 pages, 4 multi-panel figures, including one new in the final
versio
Joint Measurability and Temporal Steering
Quintino et. al. (Phys. Rev. Lett. 113, 160402 (2014)) and Uola et. al.
(Phys. Rev. Lett. 113, 160403 (2014)) have recently established an intrinsic
relation between non-joint measurability and Einstein-Podolsky- Rosen steering.
They showed that a set of measurements is incompatible (i.e., not jointly
measurable) if and only if it can be used for the demonstration of steering. In
this paper, we prove the temporal analog of this result viz., a set of
measurements are incompatible if and only if it exhibits temporal steering.Comment: 6 pages,no figures, typos corrected, improved presentation; To appear
in JOSA B feature issue "80 years of Steering and the Einstein-Podolsky-Rosen
Paradox
Entanglement of Pure Two-Mode Gaussian States
The entanglement of general pure Gaussian two-mode states is examined in
terms of the coefficients of the quadrature components of the wavefunction. The
entanglement criterion and the entanglement of formation are directly evaluated
as a function of these coefficients, without the need for deriving local
unitary transformations. These reproduce the results of other methods for the
special case of symmetric pure states which employ a relation between squeezed
states and Einstein-Podolsky-Rosen correlations. The modification of the
quadrature coefficients and the corresponding entanglement due to application
of various optical elements is also derived.Comment: 12 page
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