Many-Body Localization Implies that Eigenvectors are Matrix-Product States.

The phenomenon of many-body localization has received a lot of attention recently, both for its implications in condensed-matter physics of allowing systems to be an insulator even at nonzero temperature as well as in the context of the foundations of quantum statistical mechanics, providing examples of systems showing the absence of thermalization following out-of-equilibrium dynamics. In this work, we establish a novel link between dynamical properties--a vanishing group velocity and the absence of transport--with entanglement properties of individual eigenvectors. For systems with a generic spectrum, we prove that strong dynamical localization implies that all of its many-body eigenvectors have clustering correlations. The same is true for parts of the spectrum, thus allowing for the existence of a mobility edge above which transport is possible. In one dimension these results directly imply an entanglement area law; hence, the eigenvectors can be efficiently approximated by matrix-product states.

[Assessment of the inter- and intraobserver variability for sonographical measurement of intestinal wall thickness in dogs without gastrointestinal diseases]. / Inter- und Intraobserver-Variabilität bei der sonographischen Bestimmung der Darmwanddicke von Hunden ohne gastrointestinale Erkrankungen.

OBJECTIVE: The aim of the present study was to determine inter- and intraobserver agreement for transabdominal ultrasonographic measurements of the intestinal wall in dogs without gastrointestinal diseases. MATERIAL AND METHODS: This prospective study included 30 dogs diagnosed with a non-gastrointestinal disease and were evaluated using a transabdominal ultrasound scan in our clinic. Transverse ultrasonographic images for each segment (duodenum, jejunum, colon descendens) were obtained. These images were masked, randomized and imported as DICOM files in the OsiriX® version 5.0 program for Mac Os X. Two observers independently determined the intestinal wall thicknesses using the software inherent measurement tools. The measurements were repeated five times for each segment in all patients on 4 consecutive days. Therefore, each observer performed 1800 measurements, and 3600 measurements in total were analyzed. RESULTS: The mean values for each intestinal segment were comparable to those in the literature. The statistical analyses showed a significant positive correlation (p  <  0.01) for the inter- and intraobserver measurements at all intestinal locations. There was very high intraobserver repeatability for the measurements, with deviations of <  10%. In addition, the study displayed good interobserver reproducibility for the measurements of all intestinal segments, with variances of <  20% for the duodenum and jejunum, and <  50% for the colonic wall thickness. Even with these variances the interobserver variability for all segments was much less than the mean deviance between normal and diseased dogs. CONCLUSION AND CLINICAL RELEVANCE: Transabdominal ultrasonography is a practicable tool to assess intestinal wall thickness and integrity in small animal medicine. Our results are comparable to established reference ranges for the normal canine intestinal wall thickness. In addition, we found a good inter- and intraobserver agreement for the measurements of the canine wall thicknesses in dogs without gastrointestinal diseases.

Continuous variable quantum key distribution: finite-key analysis of composable security against coherent attacks.

We provide a security analysis for continuous variable quantum key distribution protocols based on the transmission of two-mode squeezed vacuum states measured via homodyne detection. We employ a version of the entropic uncertainty relation for smooth entropies to give a lower bound on the number of secret bits which can be extracted from a finite number of runs of the protocol. This bound is valid under general coherent attacks, and gives rise to keys which are composably secure. For comparison, we also give a lower bound valid under the assumption of collective attacks. For both scenarios, we find positive key rates using experimental parameters reachable today.