4,436 research outputs found
Modelling the spinning dust emission from LDN 1780
We study the anomalous microwave emission (AME) in the Lynds Dark Nebula
(LDN) 1780 on two angular scales. Using available ancillary data at an angular
resolution of 1 degree, we construct an SED between 0.408 GHz to 2997 GHz. We
show that there is a significant amount of AME at these angular scales and the
excess is compatible with a physical spinning dust model. We find that LDN 1780
is one of the clearest examples of AME on 1 degree scales. We detected AME with
a significance > 20. We also find at these angular scales that the
location of the peak of the emission at frequencies between 23-70 GHz differs
from the one on the 90-3000 GHz map. In order to investigate the origin of the
AME in this cloud, we use data obtained with the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) that provides 2 arcmin resolution at 30 GHz.
We study the connection between the radio and IR emissions using morphological
correlations. The best correlation is found to be with MIPS 70m, which
traces warm dust (T50K). Finally, we study the difference in radio
emissivity between two locations within the cloud. We measured a factor
of difference in 30 GHz emissivity. We show that this variation can
be explained, using the spinning dust model, by a variation on the dust grain
size distribution across the cloud, particularly changing the carbon fraction
and hence the amount of PAHs.Comment: 14 pages, 11 figures, submitted to MNRA
Characterizing the entanglement of bipartite quantum systems
We derive a separability criterion for bipartite quantum systems which
generalizes the already known criteria. It is based on observables having
generic commutation relations. We then discuss in detail the relation among
these criteria.Comment: 5 pages, 2 figures. Revised versio
Probabilistic instantaneous quantum computation
The principle of teleportation can be used to perform a quantum computation
even before its quantum input is defined. The basic idea is to perform the
quantum computation at some earlier time with qubits which are part of an
entangled state. At a later time a generalized Bell state measurement is
performed jointly on the then defined actual input qubits and the rest of the
entangled state. This projects the output state onto the correct one with a
certain exponentially small probability. The sufficient conditions are found
under which the scheme is of benefit.Comment: 4 pages, 1 figur
Quantum Cloning and Distributed Measurements
We study measurements on various subsystems of the output of a universal 1 to
2 cloning machine, and establish a correspondence between these measurements at
the output and effective measurements on the original input. We show that one
can implement sharp effective measurement elements by measuring only two out of
the three output systems. Additionally, certain complete sets of sharp
measurements on the input can be realised by measurements on the two clones.
Furthermore, we introduce a scheme that allows to restore the original input in
one of the output bits, by using measurements and classical communication -- a
protocol that resembles teleportation.Comment: submitted to Phys. Rev.
Quantum Entanglement in Second-quantized Condensed Matter Systems
The entanglement between occupation-numbers of different single particle
basis states depends on coupling between different single particle basis states
in the second-quantized Hamiltonian. Thus in principle, interaction is not
necessary for occupation-number entanglement to appear. However, in order to
characterize quantum correlation caused by interaction, we use the eigenstates
of the single-particle Hamiltonian as the single particle basis upon which the
occupation-number entanglement is defined. Using the proper single particle
basis, we discuss occupation-number entanglement in important eigenstates,
especially ground states, of systems of many identical particles. The
discussions on Fermi systems start with Fermi gas, Hatree-Fock approximation,
and the electron-hole entanglement in excitations. The entanglement in a
quantum Hall state is quantified as -fln f-(1-f)ln(1-f), where f is the proper
fractional part of the filling factor. For BCS superconductivity, the
entanglement is a function of the relative momentum wavefunction of the Cooper
pair, and is thus directly related to the superconducting energy gap. For a
spinless Bose system, entanglement does not appear in the
Hatree-Gross-Pitaevskii approximation, but becomes important in the Bogoliubov
theory.Comment: 11 pages. Journal versio
The rapidly pulsating sdO star, SDSS J160043.6+074802.9
A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system
containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields
Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely
type of K3V for the secondary star. We compare our results with atmospheric
parameters derived by Fontaine et al. (2008) and in the context of existing
evolution models for sdO stars. New and more extensive photometry is also
presented which recovers most, but not all, frequencies found in an earlier
paper. It therefore seems probable that some pulsation modes have variable
amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO
models show those having log g > 5.3 to be more likely to be unstable and
capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009
September
Detecting genuine multipartite continuous-variable entanglement
We derive necessary conditions in terms of the variances of position and
momentum linear combinations for all kinds of separability of a multi-party
multi-mode continuous-variable state. Their violations can be sufficient for
genuine multipartite entanglement, provided the combinations contain both
conjugate variables of all modes. Hence a complete state determination, for
example by detecting the entire correlation matrix of a Gaussian state, is not
needed.Comment: 13 pages, 3 figure
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