4,886 research outputs found
Entanglement creation and distribution on a graph of exchange-coupled qutrits
We propose a protocol that allows both the creation and distribution of
entanglement, resulting in two distant parties (Alice and Bob) conclusively
sharing a bipartite Bell State. The system considered is a graph of three-level
objects ("qutrits") coupled by SU(3) exchange operators. The protocol begins
with a third party (Charlie) encoding two lattice sites in unentangled states,
and allowing unitary evolution under time. Alice and Bob perform a projective
measurement on their respective qutrits at a given time, and obtain a
maximally-entangled Bell state with a certain probablility. We also consider
two further protocols, one based on simple repetition and the other based on
successive measurements and conditional resetting, and show that the cumulative
probability of creating a Bell state between Alice and Bob tends to unity.Comment: Added seven references, clarified argument for eqn (16
Effect of inhomogeneities on the expansion rate of the Universe
While the expansion rate of a homogeneous isotropic Universe is simply
proportional to the square-root of the energy density, the expansion rate of an
inhomogeneous Universe also depends on the nature of the density
inhomogeneities. In this paper we calculate to second order in perturbation
variables the expansion rate of an inhomogeneous Universe and demonstrate
corrections to the evolution of the expansion rate. While we find that the mean
correction is small, the variance of the correction on the scale of the Hubble
radius is sensitive to the physical significance of the unknown spectrum of
density perturbations beyond the Hubble radius.Comment: 19 pages, 2 figures Version 2 includes some changes in numerical
factors and corrected typos. It is the version accepted for publication in
Physical review
Topics in Cubic Special Geometry
We reconsider the sub-leading quantum perturbative corrections to N=2 cubic
special Kaehler geometries. Imposing the invariance under axion-shifts, all
such corrections (but the imaginary constant one) can be introduced or removed
through suitable, lower unitriangular symplectic transformations, dubbed
Peccei-Quinn (PQ) transformations. Since PQ transformations do not belong to
the d=4 U-duality group G4, in symmetric cases they generally have a
non-trivial action on the unique quartic invariant polynomial I4 of the charge
representation R of G4. This leads to interesting phenomena in relation to
theory of extremal black hole attractors; namely, the possibility to make
transitions between different charge orbits of R, with corresponding change of
the supersymmetry properties of the supported attractor solutions. Furthermore,
a suitable action of PQ transformations can also set I4 to zero, or vice versa
it can generate a non-vanishing I4: this corresponds to transitions between
"large" and "small" charge orbits, which we classify in some detail within the
"special coordinates" symplectic frame. Finally, after a brief account of the
action of PQ transformations on the recently established correspondence between
Cayley's hyperdeterminant and elliptic curves, we derive an equivalent,
alternative expression of I4, with relevant application to black hole entropy.Comment: 1+39 page
Entanglement recovery in noisy binary quantum information protocols via three-qubit quantum error correction codes
The task of preserving entanglement against noises is of crucial importance
for both quantum communication and quantum information transfer. To this aim,
quantum error correction (QEC) codes may be employed to compensate, at least
partially, the detriments induced by environmental noise that can be modelled
as a bit-flip or a phase-flip error channel. In this paper we investigate the
effects of the simple three-qubit QEC codes to restore entanglement and
nonlocality in a two-qubit system and consider two practical applications:
superdense coding and quantum teleportation. Though the considered three-qubit
QEC codes are known to perfectly work in the presence of very small noise, we
show that they can avoid the sudden death of entanglement and improve the
performance of the addressed protocols also for larger noise amplitudes.Comment: 14 pages, 7 figure
Some new well-posedness results for continuity and transport equations, and applications to the chromatography system
We obtain various new well-posedness results for continuity and transport
equations, among them an existence and uniqueness theorem (in the class of
strongly continuous solutions) in the case of nearly incompressible vector
fields, possibly having a blow-up of the BV norm at the initial time. We apply
these results (valid in any space dimension) to the k x k chromatography system
of conservation laws and to the k x k Keyfitz and Kranzer system, both in one
space dimension.Comment: 33 pages, minor change
Quantifying the Reversible Association of Thermosensitive Nanoparticles
Under many conditions, biomolecules and nanoparticles associate by means of
attractive bonds, due to hydrophobic attraction. Extracting the microscopic
association or dissociation rates from experimental data is complicated by the
dissociation events and by the sensitivity of the binding force to temperature
(T). Here we introduce a theoretical model that combined with light-scattering
experiments allows us to quantify these rates and the reversible binding energy
as a function of T. We apply this method to the reversible aggregation of
thermoresponsive polystyrene/poly(N-isopropylacrylamide) core-shell
nanoparticles, as a model system for biomolecules. We find that the binding
energy changes sharply with T, and relate this remarkable switchable behavior
to the hydrophobic-hydrophilic transition of the thermosensitive nanoparticles
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Numerical investigation of oil injection in a Roots blower operated as expander
The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. At the same time, these devices often serve as compressor in Vapor-Compression Refrigeration Systems. In both cases, the application of Computation Fluid Dynamics (CFD) to optimize such machines has become an integrated tool in the design process. As a consequence, several challenges associated with the numerical simulation have to be taken into account. For example, the modeling of the gap represents a challenge for the stability of the numerical analysis. The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care. To raise the efficiency of the machine, oil is typically injected. Its numerical modeling imply an extra challenge in the simulation of the actual operation of the machine. The present work is mainly focused on the multi-phase nature of the flow, with a particular analysis of the lubricant oil injected. In this work, a two-lobe Roots blower operated as expander has been simulated with the open-source software OpenFOAM-v1812, using the SCORG-V5.2.2. This analysis highlights the areas that are affected the most by the oil presence in order to highlight the sealing effect it provides
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