1,417 research outputs found
General criterion for oblivious remote state preparation
A necessary and sufficient condition is given for general exact remote state
preparation (RSP) protocols to be oblivious, that is, no information about the
target state can be retrieved from the classical message. A novel criterion in
terms of commutation relations is also derived for the existence of
deterministic exact protocols in which Alice's measurement eigenstates are
related to each other by fixed linear operators similar to Bob's unitaries. For
non-maximally entangled resources, it provides an easy way to search for RSP
protocols. As an example, we show how to reduce the case of partially entangled
resources to that of maximally entangled ones, and we construct RSP protocols
exploiting the structure of the irreducible representations of Abelian groups.Comment: 5 pages, RevTe
Combining Spatial and Temporal Logics: Expressiveness vs. Complexity
In this paper, we construct and investigate a hierarchy of spatio-temporal
formalisms that result from various combinations of propositional spatial and
temporal logics such as the propositional temporal logic PTL, the spatial
logics RCC-8, BRCC-8, S4u and their fragments. The obtained results give a
clear picture of the trade-off between expressiveness and computational
realisability within the hierarchy. We demonstrate how different combining
principles as well as spatial and temporal primitives can produce NP-, PSPACE-,
EXPSPACE-, 2EXPSPACE-complete, and even undecidable spatio-temporal logics out
of components that are at most NP- or PSPACE-complete
Continuous variable remote state preparation
We extend exact deterministic remote state preparation (RSP) with minimal
classical communication to quantum systems of continuous variables. We show
that, in principle, it is possible to remotely prepare states of an ensemble
that is parameterized by infinitely many real numbers, i.e., by a real
function, while the classical communication cost is one real number only. We
demonstrate continuous variable RSP in three examples using (i) quadrature
measurement and phase space displacement operations, (ii) measurement of the
optical phase and unitaries shifting the same, and (iii) photon counting and
photon number shift.Comment: 7 pages, RevTeX
New ATLAS9 And MARCS Model Atmosphere Grids for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
We present a new grid of model photospheres for the SDSS-III/APOGEE survey of
stellar populations of the Galaxy, calculated using the ATLAS9 and MARCS codes.
New opacity distribution functions were generated to calculate ATLAS9 model
photospheres. MARCS models were calculated based on opacity sampling
techniques. The metallicity ([M/H]) spans from -5 to 1.5 for ATLAS and -2.5 to
0.5 for MARCS models. There are three main differences with respect to previous
ATLAS9 model grids: a new corrected H2O linelist, a wide range of carbon
([C/M]) and alpha element [alpha/M] variations, and solar reference abundances
from Asplund et al. 2005. The added range of varying carbon and alpha element
abundances also extends the previously calculated MARCS model grids. Altogether
1980 chemical compositions were used for the ATLAS9 grid, and 175 for the MARCS
grid. Over 808 thousand ATLAS9 models were computed spanning temperatures from
3500K to 30000K and log g from 0 to 5, where larger temperatures only have high
gravities. The MARCS models span from 3500K to 5500K, and log g from 0 to 5.
All model atmospheres are publically available online.Comment: 8 pages, 6 figures, 5 tables, accepted for publication in The
Astronomical Journa
The Origin of Enhanced Activity in the Suns of M67
We report the results of the analysis of high resolution photospheric line
spectra obtained with the UVES instrument on the VLT for a sample of 15
solar-type stars selected from a recent survey of the distribution of H and K
chromospheric line strengths in the solar-age open cluster M67. We find upper
limits to the projected rotation velocities that are consistent with solar-like
rotation (i.e., v sini ~< 2-3 km/s) for objects with Ca II chromospheric
activity within the range of the contemporary solar cycle. Two solar-type stars
in our sample exhibit chromospheric emission well in excess of even solar
maximum values. In one case, Sanders 1452, we measure a minimum rotational
velocity of vsini = 4 +/- 0.5 km/s, or over twice the solar equatorial
rotational velocity. The other star with enhanced activity, Sanders 747, is a
spectroscopic binary. We conclude that high activity in solar-type stars in M67
that exceeds solar levels is likely due to more rapid rotation rather than an
excursion in solar-like activity cycles to unusually high levels. We estimate
an upper limit of 0.2% for the range of brightness changes occurring as a
result of chromospheric activity in solar-type stars and, by inference, in the
Sun itself. We discuss possible implications for our understanding of angular
momentum evolution in solar-type stars, and we tentatively attribute the rapid
rotation in Sanders 1452 to a reduced braking efficiency.Comment: accepted by Ap
The Metallicity of the HD 98800 System
Pre-main sequence (PMS) binaries and multiples enable critical tests of
stellar models if masses, metallicities, and luminosities of the component
stars are known. We have analyzed high-resolution, high signal-to-noise echelle
spectra of the quadruple-star system HD 98800 and using spectrum synthesis,
computed fits to the composite spectrum for a full range of plausible stellar
parameters for the components. We consistently find that sub-solar metallicity
yields fits with lower values, with an overall best-fit of . This metallicity appears to be consistent with PMS evolutionary
tracks for the measured masses and luminosities of the components of HD 98800
but additional constraints on the system and modelling are needed.Comment: 6 pages, 3 figures, 5 tables. Online-only material: color figure.
Accepted in Ap
Continuous variable versus EIT-based quantum memories
We discuss a general model of a quantum memory for a single light mode in a
collective mode of atomic oscillators. The model includes interaction
Hamiltonians that are of second order in the canonical position and momentum
operators of the light- and atomic oscillator modes. We also consider the
possibility of measurement and feedback. We identify an interaction Hamiltonian
that leads to an ideal mapping by pure unitary evolution and compare several
schemes which realize this mapping using a common continuous-variable
description. In particular we discuss schemes based on the off-resonant Faraday
effect supplemented by measurement and feedback and proper preparation of the
atoms in a squeezed state and schemes based on off-resonant Raman coupling as
well as electromagnetically induced transparency (EIT).Comment: 12 pages, 4 figure
Carbon and Oxygen in Nearby Stars: Keys to Protoplanetary Disk Chemistry
We present carbon and oxygen abundances for 941 FGK stars-the largest such
catalog to date. We find that planet-bearing systems are enriched in these
elements. We self-consistently measure C/O, which is thought to play a key role
in planet formation. We identify 46 stars with C/O \geq 1.00 as potential hosts
of carbon-dominated exoplanets. We measure a downward trend in [O/Fe] versus
[Fe/H] and find distinct trends in the thin and thick disks, supporting the
work of Bensby et al. Finally, we measure sub-solar C/O = 0.40+0.11 - 0.07, for
WASP-12, a surprising result as this star is host to a transiting hot Jupiter
whose dayside atmosphere was recently reported to have C/O \geq 1 by
Madhusudhan et al. Our measurements are based on 15,000 high signal-to-noise
spectra taken with the Keck 1 telescope as part of the California Planet
Search. We derive abundances from the [O I] and C I absorption lines at
{\lambda} = 6300 and 6587 {\AA} using the SME spectral synthesizer.Comment: 108 pages (including appendix), 16 figures, 6 table
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