Approximate Degradable Quantum Channels

Degradable quantum channels are an important class of completely positive trace-preserving maps. Among other properties, they offer a single-letter formula for the quantum and the private classical capacity and are characterized by the fact that a complementary channel can be obtained from the channel by applying a degrading channel. In this work we introduce the concept of approximate degradable channels, which satisfy this condition up to some finite $\varepsilon\geq0$. That is, there exists a degrading channel which upon composition with the channel is $\varepsilon$-close in the diamond norm to the complementary channel. We show that for any fixed channel the smallest such $\varepsilon$ can be efficiently determined via a semidefinite program. Moreover, these approximate degradable channels also approximately inherit all other properties of degradable channels. As an application, we derive improved upper bounds to the quantum and private classical capacity for certain channels of interest in quantum communication.Comment: v3: minor changes, published version. v2: 21 pages, 2 figures, improved bounds on the capacity for approximate degradable channels based on [arXiv:1507.07775], an author adde

Universal recovery maps and approximate sufficiency of quantum relative entropy

The data processing inequality states that the quantum relative entropy between two states $\rho$ and $\sigma$ can never increase by applying the same quantum channel $\mathcal{N}$ to both states. This inequality can be strengthened with a remainder term in the form of a distance between $\rho$ and the closest recovered state $(\mathcal{R} \circ \mathcal{N})(\rho)$, where $\mathcal{R}$ is a recovery map with the property that $\sigma = (\mathcal{R} \circ \mathcal{N})(\sigma)$. We show the existence of an explicit recovery map that is universal in the sense that it depends only on $\sigma$ and the quantum channel $\mathcal{N}$ to be reversed. This result gives an alternate, information-theoretic characterization of the conditions for approximate quantum error correction.Comment: v3: 24 pages, 1 figure, final version published in Annales Henri Poincar\'

Vernetzte Sphären' als Herausforderung für eine moderne Ordnungspolitik

Die zunehmende Verflechtung von Staat, Wirtschaft und Zivilgesellschaft stellt die Ordnungspolitik vor ein Dilemma: Die Kluft zwischen dem eigenen Steuerungsanspruch und der faktischen Steuerungsfähigkeit wird immer größer. Wie ist diese Entwicklung zu bewerten? In welchem Rahmen kann der Staat agieren? --

Modellierung und Analyse von Wanderwellen in Hohlzylindern beim Ultraschall-Wanderwellentransport von Schüttgütern

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Hypriot Cluster Lab: An ARM-Powered Cloud Solution Utilizing Docker

Following the establishment of virtualization approaches, cloud services within data center environments have become easily manageable. Modern infrastructures use virtual machines as a platform for service delivery, requiring powerful servers. Conjointly, the uprising of the Internet of Things implies new challenges to provide applications that can successfully manage data and communicate with a large number of connected devices. The standards of entry have resulted in extreme difficulties for small enterprises and educational institutions trying to provide their own virtualized services. The Hypriot Cluster Lab (HCL) - made publicly available on Github1 - offers cloud functionality while running on ARM processors, thereby minimizing costs. Due to the fact that such processors offer less computational power, services are packaged into lightweight containers built using the Docker framework, which avoid the overhead associated with virtual machine

CortiLove: A pilot study on hair steroids in the context of being in love and separation

While romantic infatuation and separation influence psychological and physiological functioning, the hypothalamic-pituitary-adrenal axis with its biomarkers cortisol, dehydroepiandrosterone (DHEA), and progesterone central for coping and distress has been scarcely researched in this context. In particular, endocrine hair analyses assumed to be more valid than saliva or blood assessments for studying long-term processes have not yet been conducted in the context of romantic love. Thus, 101 female subjects in phases of infatuation (n = 16), separation (n = 14), long-term relationships (n = 40), and singlehood (n = 31) reported psychological distress and provided 1 cm hair samples for the assessment of long-term integrated cortisol, DHEA, and progesterone over the last month. Separated, infatuated, and single women exhibited higher cortisol levels than those in a long-term relationship (all ps ≤ .031), while self-reported distress was only evident in separated individuals. Further, no group differences for progesterone (p = .602), but higher DHEA levels in the separation (p = .009) and single group (p = .016) compared to the long-term relationship group were detected. This is the first study showing that compared to women in long-term relationships, infatuation, separation, and single groups exhibit higher levels of physiological, but not necessarily self-reported indicators of distress. These findings, albeit on a very small and preliminary sample, are discussed in the context of the stress-buffering effect of relationships, and provide important starting points for bigger, more balanced studies combining multimodal self-report and biological markers in psychological research of romantic love

Revisiting the vortex-core tunnelling spectroscopy in YBa2_2Cu3_3O7−δ_{7-\delta}

The observation by scanning tunnelling spectroscopy (STS) of Abrikosov vortex cores in the high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterised by a strong zero-bias conductance peak. We present STS data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel which contributes to the tunnelling signal in parallel with the superconducting density of states.Comment: Final version with supplementary materia

Acute epiglottitis after COVID-19 infection

In patients with acute epiglottitis, the possibility of COVID-19 should be ruled out. Repeated nasofiberoscopy examinations or a tracheostomy, which may produce infectious aerosols, may be required.Peer reviewe