8,558 research outputs found
Further Criteria for the Existence of Steady Line-Driven Winds
In Paper I, we showed that steady line-driven disk wind solutions can exist
by using "simple" models that mimic the disk environment. Here I extend the
concepts introduced in Paper I and discuss many details of the analysis of the
steady/unsteady nature of 1D line-driven winds. This work confirms the results
and conclusions of Paper I, and is thus consistent with the steady nature of
the 1D streamline line-driven disk wind models of Murray and collaborators and
the 2.5D line-driven disk wind models of Pereyra and collaborators. When
including gas pressures effects, as is routinely done in time-dependent
numerical models, I find that the spatial dependence of the nozzle function
continues to play a key role in determining the steady/unsteady nature of
supersonic line-driven wind solutions. I show here that the
existence/nonexistence of local wind solutions can be proved through the nozzle
function without integrating the equation of motion. This work sets a detailed
framework with which we will analyze, in a following paper, more realistic
models than the "simple" models of Paper I.Comment: 30 pages, 5 figures, accepted for publication by The Astrophysical
Journa
Scaling of Entanglement Entropy in the Random Singlet Phase
We present numerical evidences for the logarithmic scaling of the
entanglement entropy in critical random spin chains. Very large scale exact
diagonalizations performed at the critical XX point up to L=2000 spins 1/2 lead
to a perfect agreement with recent real-space renormalization-group predictions
of Refael and Moore [Phys. Rev. Lett. {\bf 93}, 260602 (2004)] for the
logarithmic scaling of the entanglement entropy in the Random Singlet Phase
with an effective central charge . Moreover we
provide the first visual proof of the existence the Random Singlet Phase thanks
to the quantum entanglement concept.Comment: 4 pages, 3 figure
Equivalence between two-qubit entanglement and secure key distribution
We study the problem of secret key distillation from bipartite states in the
scenario where Alice and Bob can only perform measurements at the single-copy
level and classically process the obtained outcomes. Even with these
limitations, secret bits can be asymptotically distilled by the honest parties
from any two-qubit entangled state, under any individual attack. Our results
point out a complete equivalence between two-qubit entanglement and secure key
distribution: a key can be established through a one-qubit channel if and only
if it allows to distribute entanglement. These results can be generalized to
higher dimension for all those states that are one-copy distillable.Comment: 5 pages, REVTEX. Accepted version + added appendix. Proof of the main
result and discussion improved, conclusions unchange
Current noise through a Kondo quantum dot in a SU(N) Fermi liquid state
The current noise through a mesoscopic quantum dot is calculated and analyzed
in the Fermi liquid regime of the SU(N) Kondo model. Results connect the
Johnson-Nyquist noise to the shot noise for an arbitrary ratio of voltage and
temperature, and show that temperature corrections are sizeable in usual
experiments. For the experimentally relevant SU(4) case, quasiparticle
interactions are shown to increase the shot noise.Comment: 4 pages, 2 figures, to be published in Phys. Rev. Lett. (revised
version
Capacity of a bosonic memory channel with Gauss-Markov noise
We address the classical capacity of a quantum bosonic memory channel with
additive noise, subject to an input energy constraint. The memory is modeled by
correlated noise emerging from a Gauss-Markov process. Under reasonable
assumptions, we show that the optimal modulation results from a "quantum
water-filling" solution above a certain input energy threshold, similar to the
optimal modulation for parallel classical Gaussian channels. We also derive
analytically the optimal multimode input state above this threshold, which
enables us to compute the capacity of this memory channel in the limit of an
infinite number of modes. The method can also be applied to a more general
noise environment which is constructed by a stationary Gauss process. The
extension of our results to the case of broadband bosonic channels with colored
Gaussian noise should also be straightforward.Comment: 11 pages, 4 figures, final corrections mad
Decomposition of fractional quantum Hall states: New symmetries and approximations
We provide a detailed description of a new symmetry structure of the monomial
(Slater) expansion coefficients of bosonic (fermionic) fractional quantum Hall
states first obtained in Ref. 1, which we now extend to spin-singlet states. We
show that the Haldane-Rezayi spin-singlet state can be obtained without exact
diagonalization through a differential equation method that we conjecture to be
generic to other FQH model states. The symmetry rules in Ref. 1 as well as the
ones we obtain for the spin singlet states allow us to build approximations of
FQH states that exhibit increasing overlap with the exact state (as a function
of system size). We show that these overlaps reach unity in the thermodynamic
limit even though our approximation omits more than half of the Hilbert space.
We show that the product rule is valid for any FQH state which can be written
as an expectation value of parafermionic operators.Comment: 22 pages, 8 figure
Rotating superfluids in anharmonic traps: From vortex lattices to giant vortices
We study a superfluid in a rotating anharmonic trap and explicate a rigorous
proof of a transition from a vortex lattice to a giant vortex state as the
rotation is increased beyond a limiting speed determined by the interaction
strength. The transition is characterized by the disappearance of the vortices
from the annulus where the bulk of the superfluid is concentrated due to
centrifugal forces while a macroscopic phase circulation remains. The analysis
is carried out within two-dimensional Gross-Pitaevskii theory at large coupling
constant and reveals significant differences between 'soft' anharmonic traps
(like a quartic plus quadratic trapping potential) and traps with a fixed
boundary: In the latter case the transition takes place in a parameter regime
where the size of vortices is very small relative to the width of the annulus
whereas in 'soft' traps the vortex lattice persists until the width of the
annulus becomes comparable to the vortex cores. Moreover, the density profile
in the annulus where the bulk is concentrated is, in the 'soft' case,
approximately gaussian with long tails and not of the Thomas-Fermi type like in
a trap with a fixed boundary.Comment: Published version. Typos corrected, references adde
Experimental Implementation of a Concatenated Quantum Error-Correcting Code
Concatenated coding provides a general strategy to achieve the desired level
of noise protection in quantum information storage and transmission. We report
the implementation of a concatenated quantum error-correcting code able to
correct against phase errors with a strong correlated component. The experiment
was performed using liquid-state nuclear magnetic resonance techniques on a
four spin subsystem of labeled crotonic acid. Our results show that
concatenation between active and passive quantum error-correcting codes offers
a practical tool to handle realistic noise contributed by both independent and
correlated errors.Comment: 4 pages, 2 encapsulated eps figures. REVTeX4 styl
D-branes and orientifolds of SO(3)
We study branes and orientifolds on the group manifold of SO(3). We consider
particularly the case of the equatorial branes, which are projective planes. We
show that a Dirac-Born-Infeld action can be defined on them, although they are
not orientable. We find that there are two orientifold projections with the
same spacetime action, which differ by their action on equatorial branes.Comment: 11 pages, no figure, uses JHEP3.cls. V2 : minor correction
A photometrically and spectroscopically confirmed population of passive spiral galaxies
We have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z < 0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000 Å breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and integral field spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation
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