1,105 research outputs found
Hidden entanglement, system-environment information flow and non-Markovianity
It is known that entanglement dynamics of two noninteracting qubits, locally
subjected to classical environments, may exhibit revivals. A simple explanation
of this phenomenon may be provided by using the concept of hidden entanglement,
which signals the presence of entanglement that may be recovered without the
help of nonlocal operations. Here we discuss the link between hidden
entanglement and the (non-Markovian) flow of classical information between the
system and the environment.Comment: 9 pages, 2 figures; proceedings of the conference IQIS 2013,
September 24-26 2013, Como, Ital
Hidden entanglement in the presence of random telegraph dephasing noise
Entanglement dynamics of two noninteracting qubits, locally affected by
random telegraph noise at pure dephasing, exhibits revivals. These revivals are
not due to the action of any nonlocal operation, thus their occurrence may
appear paradoxical since entanglement is by definition a nonlocal resource. We
show that a simple explanation of this phenomenon may be provided by using the
(recently introduced) concept of "hidden" entanglement, which signals the
presence of entanglement that may be recovered with the only help of local
operations.Comment: 8 pages, 1 figure, submitted to Physica Scripta on September 17th
201
Local-global questions for divisibility in commutative algebraic groups
This is a survey focusing on the Hasse principle for divisibility of pointsin commutative algebraic groups and its relation with the Hasse principle fordivisibility of elements of the Tate-Shavarevich group in the Weil-Ch\^{a}teletgroup. The two local-global subjects arose as a generalization of someclassical questions considered respectively by Hasse and Cassels. We describethe deep connection between the two problems and give an overview of thelong-established results and the ones achieved during the last twenty years,when the questions were taken up again in a more general setting. Inparticular, by connecting various results about the two problems, we describehow some recent developments in the first of the two local-global questionsimply an answer to Cassel's question, which improves all the results publishedbefore about that problem. This answer is best possible over . Wealso describe some links with other similar questions, as for examples theSupport Problem and the local-global principle for existence of isogenies ofprime degree in elliptic curves.<br
Entanglement degradation in the solid state: interplay of adiabatic and quantum noise
We study entanglement degradation of two non-interacting qubits subject to
independent baths with broadband spectra typical of solid state nanodevices. We
obtain the analytic form of the concurrence in the presence of adiabatic noise
for classes of entangled initial states presently achievable in experiments. We
find that adiabatic (low frequency) noise affects entanglement reduction
analogously to pure dephasing noise. Due to quantum (high frequency) noise,
entanglement is totally lost in a state-dependent finite time. The possibility
to implement on-chip both local and entangling operations is briefly discussed.Comment: Replaced with published version. Minor change
Interactions of the Galactic bar and spiral arm in NGC 3627
Aims: To gain insight into the expected gas dynamics at the interface of the Galactic bar and spiral arms in our own Milky Way galaxy, we examine as an extragalactic counterpart the evidence of multiple distinct velocity components in the cold dense molecular gas that populates a similar region at the end of the bar in the nearby galaxy NGC 3627.
Methods: We assembled a high-resolution view of molecular gas kinematics traced by CO(2-1) emission and extracted line-of-sight velocity profiles from regions of high and low gas velocity dispersion.
Results: The high velocity dispersions arise with often double-peaked or multiple line-profiles. We compare the centroids of the different velocity components to expectations based on orbital dynamics in the presence of bar and spiral potential perturbations. A model of the region as the interface of two gas-populated orbits families supporting the bar and the independently rotating spiral arms provides an overall good match to the data. An extent of the bar to the corotation radius of the galaxy is favored.
Conclusions: Using NGC 3627 as an extragalactic example, we expect situations like this to favor strong star formation events such as are observed in our own Milky Way since gas can pile up where the orbit families cross. The relative motions of the material following these orbits is most likely even more important for the build-up of high density in the region. The surface densities in NGC 3627 are also so high that shear at the bar end is unlikely to significantly weaken the star formation activity. We speculate that scenarios in which the bar and spiral rotate at two different pattern speeds may be the most favorable for intense star formation at such interfaces
Interactions of the Galactic bar and spiral arm in NGC 3627
Aims: To gain insight into the expected gas dynamics at the interface of the Galactic bar and spiral arms in our own Milky Way galaxy, we examine as an extragalactic counterpart the evidence of multiple distinct velocity components in the cold dense molecular gas that populates a similar region at the end of the bar in the nearby galaxy NGC 3627.
Methods: We assembled a high-resolution view of molecular gas kinematics traced by CO(2-1) emission and extracted line-of-sight velocity profiles from regions of high and low gas velocity dispersion.
Results: The high velocity dispersions arise with often double-peaked or multiple line-profiles. We compare the centroids of the different velocity components to expectations based on orbital dynamics in the presence of bar and spiral potential perturbations. A model of the region as the interface of two gas-populated orbits families supporting the bar and the independently rotating spiral arms provides an overall good match to the data. An extent of the bar to the corotation radius of the galaxy is favored.
Conclusions: Using NGC 3627 as an extragalactic example, we expect situations like this to favor strong star formation events such as are observed in our own Milky Way since gas can pile up where the orbit families cross. The relative motions of the material following these orbits is most likely even more important for the build-up of high density in the region. The surface densities in NGC 3627 are also so high that shear at the bar end is unlikely to significantly weaken the star formation activity. We speculate that scenarios in which the bar and spiral rotate at two different pattern speeds may be the most favorable for intense star formation at such interfaces
ALMA polarization observations of the particle accelerators in the hot spot of the radio galaxy 3C 445
We present Atacama Large Millimeter Array (ALMA) polarization observations at
97.5 GHz of the southern hot spot of the radio galaxy 3C 445. The hot spot
structure is dominated by two bright components enshrouded by diffuse emission.
Both components show fractional polarization between 30 and 40 per cent,
suggesting the presence of shocks. The polarized emission of the western
component has a displacement of about 0.5 kpc outward with respect to the total
intensity emission, and may trace the surface of a front shock. Strong
polarization is observed in a thin strip marking the ridge of the hot spot
structure visible from radio to optical. No significant polarization is
detected in the diffuse emission between the main components, suggesting a
highly disordered magnetic field likely produced by turbulence and
instabilities in the downstream region that may be at the origin of the
extended optical emission observed in this hot spot. The polarization
properties support a scenario in which a combination of both multiple and
intermittent shock fronts due to jet dithering, and spatially distributed
stochastic second-order Fermi acceleration processes are present in the hot
spot complex.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Lette
An Analytical Solution of the Advection Dispersion Equation in a Bounded Domain and Its Application to Laboratory Experiments
We study a uniform flow in a parallel plate geometry to model contaminant transport through a saturated porous medium in a semi-infinite domain in order to simulate an experimental apparatus mainly constituted by a chamber filled with a glass beads bed. The general solution of the advection dispersion equation in a porous medium was obtained by utilizing the Jacobiθ3Function. The analytical solution here presented has been provided when the inlet (Dirac) and the boundary conditions (Dirichelet, Neumann, and mixed types) are fixed. The proposed solution was used to study experimental data acquired by using a noninvasive technique
A gas-rich AGN near the centre of a galaxy cluster at z ~ 1.4
The formation of the first virialized structures in overdensities dates back
to ~9 Gyr ago, i.e. in the redshift range z ~ 1.4 - 1.6. Some models of
structure formation predict that the star formation activity in clusters was
high at that epoch, implying large reservoirs of cold molecular gas. Aiming at
finding a trace of this expected high molecular gas content in primeval
clusters, we searched for the 12CO(2-1) line emission in the most luminous
active galactic nucleus (AGN) of the cluster around the radio galaxy 7C
1756+6520 at z ~ 1.4, one of the farthest spectroscopic confirmed clusters.
This AGN, called AGN.1317, is located in the neighbourhood of the central radio
galaxy at a projected distance of ~780 kpc. The IRAM Plateau de Bure
Interferometer was used to investigate the molecular gas quantity in AGN.1317,
observing the 12CO(2-1) emission line. We detect CO emission in an AGN
belonging to a galaxy cluster at z ~ 1.4. We measured a molecular gas mass of
1.1 x 10^10 Msun, comparable to that found in submillimeter galaxies. In
optical images, AGN.1317 does not seem to be part of a galaxy interaction or
merger.We also derived the nearly instantaneous star formation rate (SFR) from
Halpha flux obtaining a SFR ~65 Msun/yr. This suggests that AGN.1317 is
actively forming stars and will exhaust its reservoir of cold gas in ~0.2-1.0
Gyr.Comment: 5 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
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