Does three-tangle properly quantify the three-party entanglement for Greenberger-Horne-Zeilinger-type states?

Some mixed states composed of only GHZ states can be expressed in terms of only W-states. This fact implies that such states have vanishing three-tangle. One of such rank-3 states, $\Pi_{GHZ}$, is explicitly presented in this paper. These results are used to compute analytically the three-tangle of a rank-4 mixed state $\sigma$ composed of four GHZ states. This analysis with considering Bloch sphere $S^{16}$ of $d=4$ qudit system allows us to derive the hyper-polyhedron. It is shown that the states in this hyper-polyhedron have vanishing three-tangle. Computing the one-tangles for $\Pi_{GHZ}$ and $\sigma$, we prove the monogamy inequality explicitly. Making use of the fact that the three-tangle of $\Pi_{GHZ}$ is zero, we try to explain why the W-class in the whole mixed states is not of measure zero contrary to the case of pure states.Comment: 10 pages, no figure V2: new calculational results are included. 11 pages: V3 accepted in the Rapid Communication of PRA, 4 pages (two column

Near-deterministic quantum teleportation and resource-efficient quantum computation using linear optics and hybrid qubits

We propose a scheme to realize deterministic quantum teleportation using linear optics and hybrid qubits. It enables one to efficiently perform teleportation and universal linear-optical gate operations in a simple and near-deterministic manner using all-optical hybrid entanglement as off-line resources. Our analysis shows that our new approach can outperforms major previous ones when considering both the resource requirements and fault tolerance limits.Comment: 10 pages, 5 figures; extended version, title, abstract and figures changed, details added, to be published in Phys. Rev.

Direct Experimental Evidence of Metal-Mediated Etching of Suspended Graphene

Atomic resolution high angle annular dark field imaging of suspended, single-layer graphene, onto which the metals Cr, Ti, Pd, Ni, Al and Au atoms had been deposited was carried out in an aberration corrected scanning transmission electron microscope. In combination with electron energy loss spectroscopy, employed to identify individual impurity atoms, it was shown that nano-scale holes were etched into graphene, initiated at sites where single atoms of all the metal species except for gold come into close contact with the graphene. The e-beam scanning process is instrumental in promoting metal atoms from clusters formed during the original metal deposition process onto the clean graphene surface, where they initiate the hole-forming process. Our observations are discussed in the light of calculations in the literature, predicting a much lowered vacancy formation in graphene when metal ad-atoms are present. The requirement and importance of oxygen atoms in this process, although not predicted by such previous calculations, is also discussed, following our observations of hole formation in pristine graphene in the presence of Si-impurity atoms, supported by new calculations which predict a dramatic decrease of the vacancy formation energy, when SiOx molecules are present.Comment: final version accepted in ACS Nano + supplementary info. 22+6 pages, 4+5 figure

A geographical study of health services utilization among elderly in Hong Kong: from spatial variations to health care implications

Introduction: Levels of utilization of health services vary socially and geographically. Differences in the rates of usage are also associated with geographical aspects of health care systems. The purpose of this study was to capture spatial variations in hospital health services utilization in the elderly population in Hong Kong, a Special Administrative Region of China. Materials and Methods: We carried out a secondary analysis of a database from the Hospital Authority (HA) which covers 98% (N = 243,245) of the total registered deaths in Hong Kong during 1999 to 2005. Deaths at age 65y and above (N = 184,671) were included in the analysis. Age-sex weighted mean utilization ratio of hospital services was calculated by dividing the age-sex weighted mean usage of a particular service for each district by that for the whole territory. The variation in utilization by the seniors was analyzed in terms of four types of services: length of stay (LOS) in HA hospitals, number of inpatient admissions, number of visits to specialist outpatient department (SOPD), and attendances at accident and emergency department (AED). Results: Deaths at age 65y and above contributed to 76% of the total registered deaths. Each district contributed 1.0% to 9.1% of the total number of deaths in Hong Kong. Spatial analysis of the age-sex weighted mean utilization ratio showed significant geographic variation in the use of hospital services: the range of difference in the LOS between the lowest and highest district was 44%, while some differences as high as 33%, 35% and 39% in utilization ratios were observed in relation to number of inpatient admissions, visits to SOPD, and attendances at AED respectively. However, the patterns of these variations were not consistent for the four types of service being analyzed. Conclusions: Geographic variation in the utilization of hospital health services across the 18 districts in Hong Kong among the elderly population during the last three years before death was demonstrated. However, the patterns of variation were different for the types of services being examined. Further studies using primary data at an individual level are needed to explain the variations. Detailed analysis examining the relationship between service provision, accessibility and health outcomes are also indicated in order to inform the planning of health service delivery.published_or_final_versio

Disrupted functional brain network organization in patients with obstructive sleep apnea.

IntroductionObstructive sleep apnea (OSA) subjects show impaired autonomic, affective, executive, sensorimotor, and cognitive functions. Brain injury in OSA subjects appears in multiple sites regulating these functions, but the integrity of functional networks within the regulatory sites remains unclear. Our aim was to examine the functional interactions and the complex network organization of these interactions across the whole brain in OSA, using regional functional connectivity (FC) and brain network topological properties.MethodsWe collected resting-state functional magnetic resonance imaging (MRI) data, using a 3.0-Tesla MRI scanner, from 69 newly diagnosed, treatment-naïve, moderate-to-severe OSA (age, 48.3 ± 9.2 years; body mass index, 31 ± 6.2 kg/m(2); apnea-hypopnea index (AHI), 35.6 ± 23.3 events/h) and 82 control subjects (47.6 ± 9.1 years; body mass index, 25.1 ± 3.5 kg/m(2)). Data were analyzed to examine FC in OSA over controls as interregional correlations and brain network topological properties.ResultsObstructive sleep apnea subjects showed significantly altered FC in the cerebellar, frontal, parietal, temporal, occipital, limbic, and basal ganglia regions (FDR, P < 0.05). Entire functional brain networks in OSA subjects showed significantly less efficient integration, and their regional topological properties of functional integration and specialization characteristics also showed declined trends in areas showing altered FC, an outcome which would interfere with brain network organization (P < 0.05; 10,000 permutations). Brain sites with abnormal topological properties in OSA showed significant relationships with AHI scores.ConclusionsOur findings suggest that the dysfunction extends to resting conditions, and the altered FC and impaired network organization may underlie the impaired responses in autonomic, cognitive, and sensorimotor functions. The outcomes likely result from the prominent structural changes in both axons and nuclear structures, which occur in the condition

The UV Continuum of Quasars: Models and SDSS Spectral Slopes

We measure long (2200-4000 ang) and short (1450-2200 ang) wavelength spectral slopes \alpha (F_\nu proportional to \nu^\alpha) for quasar spectra from the Sloan Digital Sky Survey. The long and short wavelength slopes are computed from 3646 and 2706 quasars with redshifts in the z=0.76-1.26 and z=1.67-2.07 ranges, respectively. We calculate mean slopes after binning the data by monochromatic luminosity at 2200 ang and virial mass estimates based on measurements of the MgII line width and 3000 ang continuum luminosity. We find little evidence for mass dependent variations in the mean slopes, but a significant luminosity dependent trend in the near UV spectral slopes is observed with larger (bluer) slopes at higher luminosities. The far UV slopes show no clear variation with luminosity and are generally lower (redder) than the near UV slopes at comparable luminosities, suggesting a slightly concave quasar continuum shape. We compare these results with Monte Carlo distributions of slopes computed from models of thin accretion disks, accounting for uncertainties in the mass estimates. The model slopes produce mass dependent trends which are larger than observed, though this conclusion is sensitive to the assumed uncertainties in the mass estimates. The model slopes are also generally bluer than observed, and we argue that reddening by dust intrinsic to the source or host galaxy may account for much of the discrepancy.Comment: To be published in ApJ, 18 pages, 10 figure

Microscopic Theory of Rashba Interaction in Magnetic Metal

Theory of Rashba spin-orbit coupling in magnetic metals is worked out from microscopic Hamiltonian describing d-orbitals. When structural inversion symmetry is broken, electron hopping between $d$-orbitals generates chiral ordering of orbital angular momentum, which combines with atomic spin-orbit coupling to result in the Rashba interaction. Rashba parameter characterizing the interaction is band-specific, even reversing its sign from band to band. Large enhancement of the Rashba parameter found in recent experiments is attributed to the orbital mixing of 3d magnetic atoms with non-magnetic heavy elements as we demonstrate by first-principles and tight-binding calculations.Comment: 5 pages, 2 figure

A special irreducible matrix representation of the real Clifford algebra C(3,1)

4x4 Dirac (gamma) matrices (irreducible matrix representations of the Clifford algebras C(3,1), C(1,3), C(4,0)) are an essential part of many calculations in quantum physics. Although the final physical results do not depend on the applied representation of the Dirac matrices (e.g. due to the invariance of traces of products of Dirac matrices), the appropriate choice of the representation used may facilitate the analysis. The present paper introduces a particularly symmetric real representation of 4x4 Dirac matrices (Majorana representation) which may prove useful in the future. As a byproduct, a compact formula for (transformed) Pauli matrices is found. The consideration is based on the role played by isoclinic 2-planes in the geometry of the real Clifford algebra C(3,0) which provide an invariant geometric frame for it. It can be generalized to larger Clifford algebras.Comment: 23 pages LaTeX, to appear in the J. Math. Phys. (v2: appendix B on Pauli matrices and references are added, minor other changes