Scalable reconstruction of density matrices

Recent contributions in the field of quantum state tomography have shown that, despite the exponential growth of Hilbert space with the number of subsystems, tomography of one-dimensional quantum systems may still be performed efficiently by tailored reconstruction schemes. Here, we discuss a scalable method to reconstruct mixed states that are well approximated by matrix product operators. The reconstruction scheme only requires local information about the state, giving rise to a reconstruction technique that is scalable in the system size. It is based on a constructive proof that generic matrix product operators are fully determined by their local reductions. We discuss applications of this scheme for simulated data and experimental data obtained in an ion trap experiment.

Pinning of fermionic occupation numbers

The Pauli exclusion principle is a constraint on the natural occupation numbers of fermionic states. It has been suspected since at least the 1970s, and only proved very recently, that there is a multitude of further constraints on these numbers, generalizing the Pauli principle. Here, we provide the first analytic analysis of the physical relevance of these constraints. We compute the natural occupation numbers for the ground states of a family of interacting fermions in a harmonic potential. Intriguingly, we find that the occupation numbers are almost, but not exactly, pinned to the boundary of the allowed region (quasipinned). The result suggests that the physics behind the phenomenon is richer than previously appreciated. In particular, it shows that for some models, the generalized Pauli constraints play a role for the ground state, even though they do not limit the ground-state energy. Our findings suggest a generalization of the Hartree-Fock approximation.

Laboratory capability for molecular detection and confirmation of novel coronavirus in Europe, November 2012

A rapid survey by the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO) Regional Office for Europe ascertained the availability of national reference laboratory testing for a recently detected novel coronavirus as of 28 November 2012. Screening by internal quality controlled upE-RT-PCR assay was available in 23/46 of responding countries in the WHO European Region, of which 19/30 in European Union (EU) and European Economic Area (EEA) countries. Confirmation of positive screened samples by either ORF1b - RT-PCR, or other target RT-PCR assays with sequence analysis or whole-genome sequence analysis was available in 22/46 responding countries of which 18/30 in EU/EEA countries.

Multivariate analysis including biomarkers in the phase III RADIANT-2 study of octreotide LAR plus everolimus (E+O) or placebo (P+O) among patients with advanced neuroendocrine tumors (NET)

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Background: In this large phase III trial, median progression-free survival (PFS) improved by 5.1 mo with E+O compared to P+O in patients (pts) with NET associated with carcinoid syndrome. Baseline imbalances including WHO performance status (PS) and primary site favoring P+O confounded primary analysis. Chromogranin A (CgA) and 5-hydroxyindoleacetic acid (5-HIAA) are important biomarkers in NET. Analyses were performed to identify prognostic factors and adjust for baseline imbalances. Methods: Pts were randomized to E+O (n=216) or P+O (n=213). Potential prognostic factors including baseline CgA (≤2×ULN vs >2×ULN), baseline 5-HIAA (≤median vs >median at baseline), age (<65 vs ≥65), gender, race, WHO PS (0 vs 1, 2), primary site (lung vs other), prior somatostatin analog use (yes vs no), duration from diagnosis (<6 mo, 6-24 mo, 2-5 yr, >5 yr), and organs involved (liver, bone) were assessed in univariate analysis using the log rank test and stepwise regression using Cox proportional hazards model. Results: Median PFS (mo) was significantly longer for pts with nonelevated CgA (27 vs 11; p<.001) and nonelevated 5-HIAA (17 vs 11; p<.001). Analyses also indicated age (14 vs 12; p=.01), WHO PS (17 vs 11; p=.004), liver involvement (14 vs not reached; p=.02), bone metastases (8 vs 15; p<.001), and lung as primary site (11 vs 14; p=.06) as potentially prognostic. Multivariate analysis indicated that significant prognostic factors for PFS included baseline CgA (HR, 0.47; CI, 0.34-0.65; p<.001), WHO PS (HR, 0.69; CI, 0.52-0.90; p=.006), bone involvement (HR, 1.52; CI, 1.06-2.18; p=.02), and lung as primary site (HR, 1.55; CI, 1.01-2.36; p=.04). Adjusted for covariates, a 38% reduction in risk of progression was observed for E+O (HR, 0.62; 95% CI, 0.51-0.87; p=.003). Conclusions: In the phase III RADIANT-2 trial, baseline CgA levels, WHO PS, lung as primary site, and bone involvement were important prognostic factors. Exploratory analysis adjusted for these prognostic factors indicated significant benefit of everolimus therapy.

Multivariate analysis including biomarkers in the phase III RADIANT-2 study of octreotide LAR plus everolimus (E+O) or placebo (P+O) among patients with advanced neuroendocrine tumors (NET)

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Background: In this large phase III trial, median progression-free survival (PFS) improved by 5.1 mo with E+O compared to P+O in patients (pts) with NET associated with carcinoid syndrome. Randomization imbalances including WHO performance status (PS), and primary site favoring P+O confounded primary analysis. Chromogranin A (CgA) and 5-hydroxyindoleacetic acid (5-HIAA) are important biomarkers in NET. Analyses were performed to identify prognostic factors and adjust for randomization imbalances.

Methods: Pts were randomized to E+O (n=216) or P+O (n=213). Potential prognostic factors including baseline CgA (≤2×ULN vs >2×ULN), baseline 5-HIAA (≤median vs >median), age (<65 vs ≥65), gender, race, WHO PS (0 vs 1, 2), primary site (lung vs other), prior somatostatin analog use (yes vs no), duration from diagnosis (<6 mo, 6-24 mo, 2-5 yr, >5 yr), and organs involved (liver, bone) were assessed in univariate analysis using the log rank test and a stepwise regression using Cox proportional hazards model.

Results: Randomization resulted in significant imbalance in baseline CgA (median [ng/mL], 251 E+O vs 137 P+O). Median PFS (mo) was significantly longer for pts with nonelevated CgA (27 vs 11; P<.001) and nonelevated 5-HIAA (17 vs 11; P<.001). Analyses also indicated age (14 vs 12; P=.01), WHO PS (17 vs 11; P=.004), liver involvement (14 vs not reached; P=.02), bone metastases (8 vs 15; P<.001), and lung as primary site (11 vs 14; P=.06) as potentially prognostic. Multivariate analysis indicated that significant prognostic factors for PFS included baseline CgA (HR, 0.47; CI, 0.34-0.65; P<.001), WHO PS (HR, 0.69; CI, 0.52-0.90; P=.006), bone involvement (HR, 1.52; CI, 1.06-2.18; P=.02), and lung as primary site (HR, 1.55; CI, 1.01-2.36; P=.04). Adjusted for covariates, a 38% reduction in risk of progression was observed for E+O (HR, 0.62; 95% CI, 0.51-0.87; P=.003).

Conclusions: In the phase III RADIANT-2 trial, baseline CgA levels, WHO PS, lung as primary site, and bone involvement were important prognostic factors. Exploratory analysis adjusted for these prognostic factors indicated significant benefit for everolimus therapy.

Effectiveness of community health workers in providing outreach and education for colorectal cancer screening in Appalachian Kentucky

The purpose of this study was to examine the effectiveness of a community health worker (CHW)-delivered cancer education program designed to increase knowledge and awareness of colorectal cancer screening options. The study population was an extremely vulnerable and medically underserved geographic region in Appalachian Kentucky. CHWs enrolled participants in face-to-face visits, obtained informed consent, and administered a baseline assessment of knowledge of colorectal cancer risks and the benefits of screening and screening history. An educational intervention was then provided and participants were re-contacted 6 months later when a posttest was administered. The mean score of the 637 participants increased from 4.27 at baseline to 4.57 at follow-up (p < .001). Participants who reported asking their health care provider about colorectal cancer screening increased from 27.6% at baseline to 34.1% at follow-up (p = .013). Results suggest that CHWs were very effective at maintaining the study population; no loss to follow-up occurred. The results also showed increased knowledge and awareness about colorectal cancer screening education. Implications for social work practice, policy and research are discussed.

Artefacts in CBCT: a review

Artefacts are common in today's cone beam CT (CBCT). They are induced by discrepancies between the mathematical modelling and the actual physical imaging process. Since artefacts may interfere with the diagnostic process performed on CBCT data sets, every user should be aware of their presence. This article aims to discuss the most prominent artefacts identified in the scientific literature and review the existing knowledge on these artefacts. We also briefly review the basic three-dimensional (3D) reconstruction concept applied by today's CBCT scanners, as all artefacts are more or less directly related to it.

Fully Coupled 3-D Modelling of Ferroelectric Polycrystalline Material Behavior

A thermodynamically consistent phenomenological model for the material behavior of polycrystalline ferroelectric ceramics is presented. The internal state of the material is described by two internal state variables. The first one is a second-order texture tensor, determining a simple orientation distribution function (ODF) for the axes of the crystal unit cells. The second is the vector of relative irreversible polarization. The irreversible strains are derived from the ODF by volume averaging. The polarization saturation states are calculated by summing up the possible contributions of all cells to the overall polarization. An invariant formulation of the piezoelectric law is applied. Analogous to the thermodynamical framework of rate-independent plasticity, driving forces and evolution laws for the internal state variables are established. Saturation and coupling of the switching behavior are governed by energy barrier functions introduced in the electric enthalpy function. Numerical examples illustrate the models capabilities.

Permutationally invariant quantum tomography

We present a scalable method for the tomography of large multiqubit quantum registers. It acquires information about the permutationally invariant part of the density operator, which is a good approximation to the true state in many relevant cases. Our method gives the best measurement strategy to minimize the experimental effort as well as the uncertainties of the reconstructed density matrix. We apply our method to the experimental tomography of a photonic four-qubit symmetric Dicke state.

Probing the negative Wigner function of a pulsed single photon point by point

We investigate quantum properties of pulsed light fields point by point in phase space. We probe the negative region of the Wigner function of a single photon generated by the means of waveguided parametric down conversion. This capability is achieved by employing loss-tolerant photon-number resolving detection, allowing us to directly observe the oscillations of the photon statistics in dependence of applied displacements in phase space. Our scheme is highly mode sensitive and can reveal the single-mode character of the signal state.

Quantum state tomography via compressed sensing

We establish methods for quantum state tomography based on compressed sensing. These methods are specialized for quantum states that are fairly pure, and they offer a significant performance improvement on large quantum systems. In particular, they are able to reconstruct an unknown density matrix of dimension d and rank r using O(rdlog²d) measurement settings, compared to standard methods that require d² settings. Our methods have several features that make them amenable to experimental implementation: they require only simple Pauli measurements, use fast convex optimization, are stable against noise, and can be applied to states that are only approximately low rank. The acquired data can be used to certify that the state is indeed close to pure, so no a priori assumptions are needed.

All reversible dynamics in maximally nonlocal theories are trivial

A remarkable feature of quantum theory is nonlocality (Bell inequality violations). However, quantum correlations are not maximally nonlocal, and it is natural to ask whether there are compelling reasons for rejecting theories in which stronger violations are possible. To shed light on this question, we consider post-quantum theories in which maximally nonlocal states (nonlocal boxes) occur. We show that reversible transformations in such theories are trivial: they consist solely of local operations and permutations of systems. In particular, no correlations can be created; nonlocal boxes cannot be prepared from product states and classical computers can efficiently simulate all such processes.

Heritability of Morningness‐Eveningness and Self‐Report Sleep Measures in a Family‐Based Sample of 521 Hutterites

Individual variation in the phase and amplitude of human circadian rhythms is well known, but the impact of heritable factors on such variation is less clear. We estimated the narrow-sense heritability for selected circadian and sleep timing, quality, and duration measures among related members of the Hutterites, an endogamous, religious community (n=521 participants). "Morningness-eveningness" (M/E), a stable trait reflecting circadian phase, was evaluated using the Composite Scale (CS). Subjective sleep measures were assessed using the Sleep Timing Questionnaire. Initial analyses reconfirmed the impact of age on M/E. Previously reported correlations between M/E scores and the sleep measures were also noted, demonstrating the construct validity of the questionnaires among the participants. Following corrections for age, gender, and colony of residence, significant narrow-sense heritability was noted for M/E (23%). The heritability for subjective sleep measures (related to timing, duration, and quality) were statistically significant for all but one variable, and varied between 12.4% and 29.4%. Thus, significant heritable influences on human circadian phase and subjective sleep indices can be detected through family-based studies. In view of the impact of circadian malfunction on human health, it may be worthwhile to map genetic factors impacting circadian and sleep variation.

Supersonic quantum communication

When locally exciting a quantum lattice model, the excitation will propagate through the lattice. This effect is responsible for a wealth of nonequilibrium phenomena, and has been exploited to transmit quantum information. It is a commonly expressed belief that for local Hamiltonians, any such propagation happens at a finite "speed of sound". Indeed, the Lieb-Robinson theorem states that in spin models, all effects caused by a perturbation are essentially limited to a causal cone. We show that for meaningful translationally invariant bosonic models with nearest-neighbor interactions (addressing the challenging aspect of an experimental realization) this belief is incorrect: We prove that one can encounter accelerating excitations under the natural dynamics that allow for reliable transmission of information faster than any finite speed of sound. It also implies that the simulation of dynamics of strongly correlated bosonic models may be much harder than that of spin chains even in the low-energy sector.