561 research outputs found
Quantum computation with realistic magic-state factories
Leading approaches to fault-tolerant quantum computation dedicate a significant portion of the hardware to computational factories that churn out high-fidelity ancillas called magic states. Consequently, efficient and realistic factory design is of paramount importance. Here we present the most detailed resource assessment to date of magic-state factories within a surface code quantum computer, along the way introducing a number of techniques. We show that the block codes of Bravyi and Haah [Phys. Rev. A 86, 052329 (2012)] have been systematically undervalued; we track correlated errors both numerically and analytically, providing fidelity estimates without appeal to the union bound. We also introduce a subsystem code realization of these protocols with constant time and low ancilla cost. Additionally, we confirm that magic-state factories have space-time costs that scale as a constant factor of surface code costs. We find that the magic-state factory required for postclassical factoring can be as small as 6.3 million data qubits, ignoring ancilla qubits, assuming 10^−4 error gates and the availability of long-range interactions
Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL
We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study
the photosphere, the warm molecular layer, and the inner wind of the close-by
oxygen-rich AGB star R Doradus. We present observations in filters V,
cntH, and cnt820 and investigate the surface brightness distribution of
the star and of the polarised light produced in the inner envelope. Thanks to
second-epoch observations in cntH, we are able to see variability on
the stellar photosphere. We find that in the first epoch the surface brightness
of R Dor is asymmetric in V and cntH, the filters where molecular
opacity is stronger, while in cnt820 the surface brightness is closer to being
axisymmetric. The second-epoch observations in cntH show that the
morphology of R Dor changes completely in a timespan of 48 days to a more
axisymmetric and compact configuration. The polarised intensity is asymmetric
in all epochs and varies by between a factor of 2.3 and 3.7 with azimuth for
the different images. We fit the radial profile of the polarised intensity
using a spherically symmetric model and a parametric description of the dust
density profile, . On average, we find exponents of
that correspond to a much steeper density profile than that of
a wind expanding at constant velocity. The dust densities we derive imply an
upper limit for the dust-to-gas ratio of at 5.0
. Given the uncertainties in observations and models, this value is
consistent with the minimum values required by wind-driving models for the
onset of a wind, of . However, if the steep density
profile we find extends to larger distances from the star, the dust-to-gas
ratio will quickly become too small for the wind of R Dor to be driven by the
grains that produce the scattered light.Comment: 10 pages, 8 figures, 4 table
The relationship between quality of life (EORTC QLQ-C30) and survival in patients with gastro-oesopohageal cancer
It remains unclear whether any aspect of quality of life has a role in predicting survival in an unselected cohort of patients with gastro-oesophageal cancer. Therefore the aim of the present study was to examine the relationship between quality of life (EORTC QLQ-C30), clinico-pathological characteristics and survival in patients with gastro-oesophageal cancer. Patients presenting with gastric or oesophageal cancer, staged using the UICC tumour node metastasis (TNM) classification and who received either potentially curative surgery or palliative treatment between November 1997 and December 2002 (n=152) participated in a quality of life study, using the EORTC QLQ-C30 core questionnaire. On univariate analysis, age (P < 0.01), tumour length (P < 0.0001), TNM stage (P<0.0001), weight loss (P<0.0001), dysphagia score (P<0.001), performance status (P<0.1) and treatment (P<0.0001) were significantly associated with cancer-specific survival. EORTC QLQ-C30, physical functioning (P<0.0001), role functioning (P<0.001), cognitive functioning (P<0.01), social functioning (P<0.0001), global quality of life (P<0.0001), fatigue (P<0.0001), nausea/vomiting (P<0.01), pain (P<0.001), dyspnoea (P<0.0001), appetite loss (P<0.0001) and constipation (P<0.05) were also significantly associated with cancer-specific survival. On multivariate survival analysis, tumour stage (P<0.0001), treatment (P<0.001) and appetite loss (P<0.0001) were significant independent predictors of cancer-specific survival. The present study highlights the importance of quality of life (EORTC QLQ-C30) measures, in particular appetite loss, as a prognostic factor in these patients
Exploring Pompeii: discovering hospitality through research synergy
Hospitality research continues to broaden through an ever-increasing dialogue and alignment with a greater number of academic disciplines. This paper demonstrates how an enhanced understanding of hospitality can be achieved through synergy between archaeology, the classics and sociology. It focuses on classical Roman life, in particular Pompeii, to illustrate the potential for research synergy and collaboration, to advance the debate on hospitality research and to encourage divergence in research approaches. It demonstrates evidence of commercial hospitality activities through the excavation hotels, bars and taverns, restaurants and fast food sites. The paper also provides an example of the benefits to be gained from multidisciplinary analysis of hospitality and tourism
Magnetically aligned dust and SiO maser polarisation in the envelope of the red supergiant VY Canis Majoris
International audienceWe use Atacama Large Millimeter/submillimeter Array Band 5 science verification observations of the red supergiant VY CMa to study the polarization of SiO thermal/masers lines and dust continuum at ~1.7 mm wavelength. We analyse both linear and circular polarization and derive the magnetic field strength and structure, assuming the polarization of the lines originates from the Zeeman effect, and that of the dust originates from aligned dust grains. We also discuss other effects that could give rise to the observed polarization. We detect, for the first time, significant polarization (~3%) of the circumstellar dust emission at millimeter wavelengths. The polarization is uniform with an electric vector position angle of . Varying levels of linear polarization are detected for the J=4-3 28SiO v=0, 1, 2, and 29SiO v=0, 1 lines, with the strongest polarization fraction of ~30% found for the 29SiO v=1 maser. The linear polarization vectors rotate with velocity, consistent with earlier observations. We also find significant (up to ~1%) circular polarization in several lines, consistent with previous measurements. We conclude that the detection is robust against calibration and regular instrumental errors, although we cannot yet fully rule out non-standard instrumental effects. Emission from magnetically aligned grains is the most likely origin of the observed continuum polarization. This implies that the dust is embedded in a magnetic field >13 mG. The maser line polarization traces the magnetic field structure. The magnetic field in the gas and dust is consistent with an approximately toroidal field configuration, but only higher angular resolution observations will be able to reveal more detailed field structure. If the circular polarization is due to Zeeman splitting, it indicates a magnetic field strength of ~1-3 Gauss, consistent with previous maser observations
ALMA and VLA reveal the lukewarm chromospheres of the nearby red supergiants Antares and Betelgeuse
We first present spatially resolved ALMA and VLA continuum observations of
the early-M red supergiant Antares to search for the presence of a chromosphere
at radio wavelengths. We resolve the free-free emission of the Antares
atmosphere at 11 unique wavelengths between 0.7 mm (ALMA band 8) and 10 cm (VLA
S band). The projected angular diameter is found to continually increase with
increasing wavelength, from a low of 50.7 mas at 0.7 mm up to a diameter of 431
mas at 10 cm, which corresponds to 1.35 and 11.6 times the photospheric angular
diameter, respectively. All four ALMA measurements show that the shape of the
atmosphere is elongated, with a flattening of 15% at a similar position angle.
The disk-averaged gas temperature of the atmosphere initially rises from a
value of 2700 K at 1.35 (i.e., 0.35 above the
photosphere) to a peak value of 3800 K at 2.5 , after which it
then more gradually decreases to 1650 K at 11.6 . The rise in gas
temperature between 1.35 and 2.5 is evidence for
a chromospheric temperature rise above the photosphere of a red supergiant. We
detect a clear change in the spectral index across the sampled wavelength
range, with the flux density between 0.7 mm
and 1.4 cm, which we associate with chromosphere-dominated emission, while the
flux density between 4.3 cm and 10 cm, which we
associate with wind-dominated emission. We then perform nonlocal thermal
equilibrium modeling of the far-ultraviolet radiation field of another early-M
red supergiant, Betelgeuse, and find that an additional hot (i.e., K)
chromospheric photoionization component with a much smaller filling factor must
also exist throughout the chromospheres of these stars.Comment: 12 pages, 6 figures, accepted for publication in A&
ALMA sub-mm maser and dust distribution of VY Canis Majoris
Cool, evolved stars have copious, enriched winds. The structure of these
winds and the way they are accelerated is not well known. We need to improve
our understanding by studying the dynamics from the pulsating stellar surface
to about 10 stellar radii, where radiation pressure on dust is fully effective.
Some red supergiants have highly asymmetric nebulae, implicating additional
forces. We retrieved ALMA Science Verification data providing images of sub-mm
line and continuum emission from VY CMa. This enables us to locate water masers
with milli-arcsec precision and resolve the dusty continuum. The 658-, 321- and
325-GHz masers lie in irregular, thick shells at increasing distances from the
centre of expansion. For the first time this is confirmed as the stellar
position, coinciding with a compact peak offset to the NW of the brightest
continuum emission. The maser shells (and dust formation zone) overlap but
avoid each other on tens-au scales. Their distribution is broadly consistent
with excitation models but the conditions and kinematics appear to be
complicated by wind collisions, clumping and asymmetries.Comment: Letter 4 pages, 5 figures plus appendix with 3 figures. Accepted by
Astronomy and Astrophysics Letter
An Overview of the 2014 ALMA Long Baseline Campaign
A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to
make accurate images with resolutions of tens of milliarcseconds, which at
submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop
and test this capability, a Long Baseline Campaign (LBC) was carried out from
September to late November 2014, culminating in end-to-end observations,
calibrations, and imaging of selected Science Verification (SV) targets. This
paper presents an overview of the campaign and its main results, including an
investigation of the short-term coherence properties and systematic phase
errors over the long baselines at the ALMA site, a summary of the SV targets
and observations, and recommendations for science observing strategies at long
baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also
compared to VLA 43 GHz results, demonstrating an agreement at a level of a few
percent. As a result of the extensive program of LBC testing, the highly
successful SV imaging at long baselines achieved angular resolutions as fine as
19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now
possible, and opens up new parameter space for submm astronomy.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in the
Astrophysical Journal Letters; this version with small changes to
affiliation
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