3,587 research outputs found
Distillation of GHZ states by selective information manipulation
Methods for distilling maximally entangled tripartite (GHZ) states from
arbitrary entangled tripartite pure states are described. These techniques work
for virtually any input state. Each technique has two stages which we call
primary and secondary distillation. Primary distillation produces a GHZ state
with some probability, so that when applied to an ensemble of systems, a
certain percentage is discarded. Secondary distillation produces further GHZs
from the discarded systems. These protocols are developed with the help of an
approach to quantum information theory based on absolutely selective
information, which has other potential applications.Comment: minor corrections, especially of some numerical values; conclusions
unaffecte
Probing Decoherence with Electromagnetically Induced Transparency in Superconductive Quantum Circuits
Superconductive quantum circuits (SQCs) comprise quantized energy levels that
may be coupled via microwave electromagnetic fields. Described in this way, one
may draw a close analogy to atoms with internal (electronic) levels coupled by
laser light fields. In this Letter, we present a superconductive analog to
electromagnetically induced transparency (S-EIT) that utilizes SQC designs of
present day experimental consideration. We discuss how S-EIT can be used to
establish macroscopic coherence in such systems and, thereby, utilized as a
sensitive probe of decoherence.Comment: 5 pages, 3 figure
Quantifying nonorthogonality
An exploratory approach to the possibility of analyzing nonorthogonality as a
quantifiable property is presented. Three different measures for the
nonorthogonality of pure states are introduced, and one of these measures is
extended to single-particle density matrices using methods that are similar to
recently introduced techniques for quantifying entanglement. Several
interesting special cases are considered. It is pointed out that a measure of
nonorthogonality can meaningfully be associated with a single mixed quantum
state. It is then shown how nonorthogonality can be unlocked with classical
information; this analysis reveals interesting inequalities and points to a
number of connections between nonorthogonality and entanglement.Comment: Accepted for publication in Phys. Rev.
Counterfactual entanglement and nonlocal correlations in separable states
It is shown that the outcomes of measurements on systems in separable mixed
states can be partitioned, via subsequent measurements on a disentangled
extraneous system, into subensembles that display the statistics of entangled
states. This motivates the introduction of the concept of "counterfactual"
entanglement, which can be associated with all separable mixed states including
those that are factorable. This type of entanglement gives rise to a new kind
of postselection-induced Bell inequality violation. The significance of
counterfactual entanglement, and its physical implications, are assessed
FORS spectroscopy of galaxies in the Hubble Deep Field South
We present low resolution multi-object spectroscopy of an I-band magnitude
limited (I_{AB} ~ 23--23.5) sample of galaxies located in an area centered on
the Hubble Deep Field-South (HDFS). The observations were obtained using the
Focal Reducer low dispersion Spectrograph (FORS) on the ESO Very Large
Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were
supplemented with galaxies detected in the Infrared Space Observatory's survey
of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100
galaxies for spectroscopic observations. Based on detections of several
emission lines, such as [OII]3727, H_beta and [OIII]5007, or other
spectroscopic features, we have measured accurate redshifts for 50 objects in
the central HDFS and flanking fields. The redshift range of the current sample
of galaxies is 0.6--1.2, with a median redshift of 1.13 (at I ~ 23.5 not
corrected for completeness). The sample is dominated by starburst galaxies with
only a small fraction of ellipticals (~10%). For the emission line objects, the
extinction corrected [OII]3727 line strengths yield estimates of star formation
rates in the range 0.5--30 M_solar/yr. We have used the present data to derive
the [OII]3727 luminosity function up to redshift of 1.2. When combined with
[OII]3727 luminosity densities for the local and high redshift Universe, our
results confirm the steep rise in the star formation rate (SFR) to z ~ 1.3.Comment: Tables 2 and 3 provided as separate files. Accepted for publication
by Astronomy and Astrophysic
Delayed - Choice Entanglement - Swapping with Vacuum-One Photon Quantum States
We report the experimental realization of a recently discovered quantum
information protocol by Asher Peres implying an apparent non-local quantum
mechanical retrodiction effect. The demonstration is carried out by applying a
novel quantum optical method by which each singlet entangled state is
physically implemented by a two-dimensional subspace of Fock states of a mode
of the electromagnetic field, specifically the space spanned by the vacuum and
the one photon state, along lines suggested recently by E. Knill et al., Nature
409, 46 (2001) and by M. Duan et al., Nature 414, 413 (2001). The successful
implementation of the new technique is expected to play an important role in
modern quantum information and communication and in EPR quantum non-locality
studies
Detection of an inner gaseous component in a Herbig Be star accretion disk: Near- and mid-infrared spectro-interferometry and radiative transfer modeling of MWC 147
We study the geometry and the physical conditions in the inner (AU-scale)
circumstellar region around the young Herbig Be star MWC 147 using
long-baseline spectro-interferometry in the near-infrared (NIR K-band,
VLTI/AMBER observations and PTI archive data) as well as the mid-infrared (MIR
N-band, VLTI/MIDIobservations). The emission from MWC 147 is clearly resolved
and has a characteristic physical size of approx. 1.3 AU and 9 AU at 2.2 micron
and 11 micron respectively (Gaussian diameter). The spectrally dispersed AMBER
and MIDI interferograms both show a strong increase in the characteristic size
towards longer wavelengths, much steeper than predicted by analytic disk models
assuming power-law radial temperature distributions. We model the
interferometric data and the spectral energy distribution of MWC 147 with 2-D,
frequency-dependent radiation transfer simulations. This analysis shows that
models of spherical envelopes or passive irradiated Keplerian disks (with
vertical or curved puffed-up inner rim) can easily fit the SED, but predict
much lower visibilities than observed; the angular size predicted by such
models is 2 to 4 times larger than the size derived from the interferometric
data, so these models can clearly be ruled out. Models of a Keplerian disk with
optically thick gas emission from an active gaseous disk (inside the dust
sublimation zone), however, yield a good fit of the SED and simultaneously
reproduce the absolute level and the spectral dependence of the NIR and MIR
visibilities. We conclude that the NIR continuum emission from MWC 147 is
dominated by accretion luminosity emerging from an optically thick inner
gaseous disk, while the MIR emission also contains contributions from the
outer, irradiated dust disk.Comment: 44 pages, 15 figures, accepted for publication in The Astrophysical
Journal. The quality of the figures was slightly reduced in order to comply
with the astro-ph file-size restrictions. You can find a high-quality version
of the paper at http://www.mpifr-bonn.mpg.de/staff/skraus/papers/mwc147.pd
Predicting emotions and meta-emotions at the movies
Audiences are attracted to dramas and horror movies even though negative and ambivalent emotions are likely to be experienced. Research into the seemingly paradoxical enjoyment of this kind of media entertainment has typically focused on gender- and genre-specific needs and viewing motivations. Extending this line of research, the authors focus the role of the need for affect as a more general, gender- and genre-independent predictor of individual differences in the experience of emotions and meta-emotions (i.e., evaluative thoughts and feelings about one’s emotions). The article discusses a field study of moviegoers who attended the regular screening of a drama or a horror film. Results support the assumption that individuals high in need for affect experience higher levels of negative and ambivalent emotions and evaluate their emotions more positively on the level of meta-emotions. Controlling for the Big Five personality factors does not alter these effects. The results are discussed within an extended meta-emotion framework
Music models aberrant rule decoding and reward valuation in dementia.
Aberrant rule- and reward-based processes underpin abnormalities of socio-emotional behaviour in major dementias. However, these processes remain poorly characterized. Here we used music to probe rule decoding and reward valuation in patients with frontotemporal dementia (FTD) syndromes and Alzheimer's disease (AD) relative to healthy age-matched individuals. We created short melodies that were either harmonically resolved ('finished') or unresolved ('unfinished'); the task was to classify each melody as finished or unfinished (rule processing) and rate its subjective pleasantness (reward valuation). Results were adjusted for elementary pitch and executive processing; neuroanatomical correlates were assessed using voxel-based morphometry. Relative to healthy older controls, patients with behavioural variant FTD showed impairments of both musical rule decoding and reward valuation, while patients with semantic dementia showed impaired reward valuation but intact rule decoding, patients with AD showed impaired rule decoding but intact reward valuation and patients with progressive non-fluent aphasia performed comparably to healthy controls. Grey matter associations with task performance were identified in anterior temporal, medial and lateral orbitofrontal cortices, previously implicated in computing diverse biological and non-biological rules and rewards. The processing of musical rules and reward distils cognitive and neuroanatomical mechanisms relevant to complex socio-emotional dysfunction in major dementias
Searching for star-planet magnetic interaction in CoRoT observations
Close-in massive planets interact with their host stars through tidal and
magnetic mechanisms. In this paper, we review circumstantial evidence for
star-planet interaction as revealed by the photospheric magnetic activity in
some of the CoRoT planet-hosting stars, notably CoRoT-2, CoRoT-4, and CoRoT-6.
The phenomena are discussed in the general framework of activity-induced
features in stars accompanied by hot Jupiters. The theoretical mechanisms
proposed to explain the activity enhancements possibly related with hot Jupiter
are also briefly reviewed with an emphasis on the possible effects at
photospheric level. The unique advantages of CoRoT and Kepler observations to
test these models are pointed out.Comment: Invited review paper accepted by Astrophysics and Space Science, 13
pages, 5 figure
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