845 research outputs found
A class of quantum gate entangler
We construct quantum gate entanglers for different classes of multipartite
states based on definition of W and GHZ concurrence classes. First, we review
the basic construction of concurrence classes based on orthogonal complement of
a positive operator valued measure (POVM) on quantum phase. Then, we construct
quantum gates entanglers for different classes of multi-qubit states. In
particular, we show that these operators can entangle multipartite state if
they satisfy some conditions for W and GHZ classes of states. Finally, we
explicitly give the W class and GHZ classes of quantum gate entanglers for
four-qubit states.Comment: 5 pages, accepted for publication in Physica Scripta for the
CEWQO2009 proceedings
Compact star clusters of the LMC HII region N11C
Based on imaging and spectroscopy obtained at the ESO NTT telescope and using
an efficient image analysis algorithm, we study the core of the LMC OB
association LH13, particularly the two compact stellar clusters Sk-6641 and HNT
in the HII, region N11C. We resolve Sk-6641 into 15 components and for the
first time the HNT cluster into 70 stars, and derive photometry for the
members. Moreover, from medium resolution spectroscopy we determine the
spectral types for sixteen stars in N11C. We compare the color-magnitude
diagrams of the clusters with that of the field stars and discuss the cluster
ages. With an age of ~100 Myr, the HNT cluster appears significantly older than
the very young (< 5 Myr) Sk-6641 starburst. We suggest that most of the `field'
O-stars in the core of N11C have actually been ejected from Sk-6641 through
dynamical interactions in the compact cluster. The properties of the Sk-6641
and HNT clusters suggest that we are viewing different star formation regions
lying at different distances along the same line of sight.Comment: 12 pages, 8 figure
Entanglement measure for general pure multipartite quantum states
We propose an explicit formula for an entanglement measure of pure
multipartite quantum states, then study a general pure tripartite state in
detail, and at end we give some simple but illustrative examples on four-qubits
and m-qubits states.Comment: 5 page
The invariant-comb approach and its relation to the balancedness of multipartite entangled states
The invariant-comb approach is a method to construct entanglement measures
for multipartite systems of qubits. The essential step is the construction of
an antilinear operator that we call {\em comb} in reference to the {\em
hairy-ball theorem}. An appealing feature of this approach is that for qubits
(or spins 1/2) the combs are automatically invariant under SL(2,\CC), which
implies that the obtained invariants are entanglement monotones by
construction. By asking which property of a state determines whether or not it
is detected by a polynomial SL(2,\CC) invariant we find that it is the
presence of a {\em balanced part} that persists under local unitary
transformations. We present a detailed analysis for the maximally entangled
states detected by such polynomial invariants, which leads to the concept of
{\em irreducibly balanced} states. The latter indicates a tight connection with
SLOCC classifications of qubit entanglement. \\ Combs may also help to define
measures for multipartite entanglement of higher-dimensional subsystems.
However, for higher spins there are many independent combs such that it is
non-trivial to find an invariant one. By restricting the allowed local
operations to rotations of the coordinate system (i.e. again to the
SL(2,\CC)) we manage to define a unique extension of the concurrence to
general half-integer spin with an analytic convex-roof expression for mixed
states.Comment: 17 pages, revtex4. Substantially extended manuscript (e.g. proofs
have been added); title and abstract modified
VLT/NACO near-infrared imaging and spectroscopy of N88A in the SMC
We present near-infrared imaging and spectroscopic high spatial resolution
observations of the SMC region N88 containing the bright, excited, extincted
and compact H II region N88A of size ~ 1 pc. To investigate its stellar content
and reddening, N88 was observed using spectroscopy and imagery in the JHKs- and
L'-band at a spatial resolution of ~ 0.1-0.3", using the VLT UT4 equipped with
the NAOS adaptive optics system. In order to attempt to establish if the origin
of the infra-red (IR) excess is due to bright nebulosity, circumstellar
material and/or local dust, we used Ks vs J-K colour-magnitude (CM) and JHK
colour-colour (CC) diagrams, as well as L' imagery.Our IR-data reveal in the
N88 area an IR-excess fraction of geq 30 per cent of the detected stars,as well
as an unprecedently detailed morphology of N88A. It consists of an embedded
cluster of ~3.5" (~ 1 pc) in diameter, of at least thirteen resolved stars
superposed with an unusual bright continuum centered on a very bright star. The
four brightest stars in this cluster lie red-ward of H-K geq 0.45 mag, and
could be classified as young stellar object (YSO) candidates. Four other
probable YSO candidates are also detected in N88 along a south-north bow-shaped
thin H2 filament at ~ 7" east of the young central bright star. At 0.2" east of
this star, a heavily embedded core is detected that could be a massive class I
protostar candidate. The 2.12 mu H2 image of N88A resembles a shell of diameter
~ 3" ~ 0.9 pc) centered on the bright star. The line ratios of H2 2-1 S(1) and
1-0 S(0) relative to 1-0 S(1), as well as the presence of high v lines, are
indicative of photodissociation regions, rather than shocks.Comment: 15 pages, 14 figures, accepted by Astronomy and Astrophysics, uses
pdflatex, aa.cl
Virial mass in DGP brane cosmology
We study the virial mass discrepancy in the context of a DPG brane-world
scenario and show that such a framework can offer viable explanations to
account for the mass discrepancy problem. This is done by defining a
geometrical mass that we prove to be proportional to the virial
mass. Estimating using observational data, we show that it
behaves linearly with and has a value of the order of , pointing
to a possible resolution of the virial mass discrepancy. We also obtain the
radial velocity dispersion of galaxy clusters and show that it is compatible
with the radial velocity dispersion profile of such clusters. This velocity
dispersion profile can be used to differentiate various models predicting the
virial mass.Comment: 12 pages, 1 figure, to appear in CQ
Concurrence classes for general pure multipartite states
We propose concurrence classes for general pure multipartite states based on
an orthogonal complement of a positive operator valued measure on quantum
phase. In particular, we construct class, , and
class concurrences for general pure -partite states. We give explicit
expressions for and class concurrences for general pure
three-partite states and for , , and class
concurrences for general pure four-partite states.Comment: 14 page
The LMC transition star R84 and the core of the LH 39 OB association
On the basis of sub-arcsecond optical imaging we resolve and study the core
components of the LMC OB association LH 39. The central star of the
association, the rare transition object R84, is also investigated using CASPEC
echelle spectroscopy. A new, powerful image restoration code that conserves the
fluxes allows us to obtain the magnitudes and colors of the components. We
bring out some 30 stars in a ~16"x16", area centered on R84. At a resolution of
0.19", the closest components to R84 are shown to lie at 1.1" NW and 1.7" NW
respectively of the transition star. One of these stars is the reddest star of
the field after R84 but turns out to be too faint to correspond to the red M2
supergiant previously reported to contaminate the spectrum of R84. If the
late-type spectrum is due to a line-of-sight supergiant with a luminosity
comparable to R84, it should lie closer than 0.12" to R84. The transition star
shows spectral variability between 1982 and 1991. We also note some slight
radial velocity variations of the Of emission lines over timescales of several
years. Furthermore, we discuss the apparent absence of O type stars in this
association.Comment: 14 pages, LaTex file + postscript figures, Accepted for publication
in AA main journa
Tectonic controls on residual oil saturation below the present-day fluid contact level in reservoirs of the Persian Gulf
Acknowledgments The authors would like to acknowledge, and gratefully appreciate the support of, the Aberdeen Formation Evaluation Society for their sponsorship, and Emerson (Paradigm) for providing the Geology software for the development of this study.Peer reviewedPostprin
The effect of rock type on natural water flooding and residual oil saturation below free water level and oil water contact : A case study from the Middle East
Acknowledgments The authors would like to gratefully acknowledge and appreciate the support of Aberdeen Formation Evaluation Society (AFES) and Baker Hughes for their sponsorship and Emerson for providing Geolog software for development of this study.Peer reviewedPostprin
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