6,731 research outputs found

    Enhanced current noise correlations in a Coulomb-Majorana device

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    Majorana bound states (MBSs) nested in a topological nanowire are predicted to manifest nonlocal correlations in the presence of a finite energy splitting between the MBSs. However, the signal of the nonlocal correlations has not yet been detected in experiments. A possible reason is that the energy splitting is too weak and seriously affected by many system parameters. Here we investigate the charging energy induced nonlocal correlations in a hybrid device of MBSs and quantum dots. The nanowire that hosts the MBSs is assumed in proximity to a mesoscopic superconducting island with a finite charging energy. Each end of the nanowire is coupled to one lead via a quantum dot with resonant levels. With a floating superconducting island, the devices shows a negative differential conductance and giant super-Poissonian shot noise, due to the interplay between the nonlocality of the MBSs and dynamical Coulomb blockade effect. When the island is strongly coupled to a bulk superconductor, the current cross correlations at small lead chemical potentials are negative by tuning the dot energy levels. In contrast, the cross correlation is always positive in a non-Majorana setup. This difference may provide a signature for the existence of the MBSs.Comment: 11 pages, 10 figure

    Quantum impurity in the bulk of topological insulator

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    We investigate physical properties of an Anderson impurity embedded in the bulk of a topological insulator. The slave-boson mean-field approximation is used to account for the strong electron correlation at the impurity. Different from the results of a quantum impurity on the surface of a topological insulator, we find for the band-inverted case, a Kondo resonant peak and in-gap bound states can be produced simultaneously. However, only one type of them appears for the normal case. It is shown that the mixed-valence regime is much broader in the band-inverted case, while it shrinks to a very narrow regime in the normal case. Furthermore, a self-screening of the Kondo effect may appear when the interaction between the bound-state spin and impurity spin is taken into account.Comment: 11 pages, 8 figure

    Semi-Supervised Learning for Neural Keyphrase Generation

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    We study the problem of generating keyphrases that summarize the key points for a given document. While sequence-to-sequence (seq2seq) models have achieved remarkable performance on this task (Meng et al., 2017), model training often relies on large amounts of labeled data, which is only applicable to resource-rich domains. In this paper, we propose semi-supervised keyphrase generation methods by leveraging both labeled data and large-scale unlabeled samples for learning. Two strategies are proposed. First, unlabeled documents are first tagged with synthetic keyphrases obtained from unsupervised keyphrase extraction methods or a selflearning algorithm, and then combined with labeled samples for training. Furthermore, we investigate a multi-task learning framework to jointly learn to generate keyphrases as well as the titles of the articles. Experimental results show that our semi-supervised learning-based methods outperform a state-of-the-art model trained with labeled data only.Comment: To appear in EMNLP 2018 (12 pages, 7 figures, 6 tables

    A Study of Key Management for Encrypted Storage in Storage Area Network

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    As secure storage becomes more pervasive throughout the enterprise, the focus quickly moves from implementing encrypting storage devices to establishing effective and secure key management policies. Without the proper key generation, distribution, storage, and recovery, valuable data will be eventually compromised [9]. Although a considerable amount of research has been dedicated to encryption algorithms in the past decades, key management becomes an issue due to the quantity of data. For example, with millions of data you will need million set of keys. To manage and keep track of these keys, complexity and operational inefficiency becomes an issue. How to manage keys becomes a challenging task. Adequate understanding of these new challenges is essential to effectively devise new key management policies and mechanisms to guard against them. We discuss many of these methods in this new context to fill this gap.Storage Security, Key Management, Storage Area Network

    Lifshitz and Schrodinger Vacua, Superstar Resolution in Gauged Maximal Supergravities

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    We consider the subset of gauged maximal supergravities that consists of the SO(n+1) gauge fields A^{ij} and the scalar deformation T^{ij} of the S^n in the spherical reduction of M-theory or type IIB. We focus on the Abelian Cartan subgroup and the diagonal entries of T^{ij}. The resulting theories can be viewed as the STU models with additional hyperscalars. We find that the theories with only one or two such vectors can be generalized naturally to arbitrary dimensions. The same is true for the D=4 or 5 Einstein-Maxwell theory with such a hyperscalar. The gauge fields become massive, determined by stationary points of the hyperscalars a la the analogous Abelian Higgs mechanism. We obtain classes of Lifshitz and Schrodinger vacua in these theories. The scaling exponent z turns out to be rather restricted, taking fractional or irrational numbers. Tweaking the theories by relaxing the mass parameter or making a small change of the superpotential, we find that solutions with z=2 can emerge. In a different application, we find that the resolution of superstar singularity in the STU models by using bubbling-AdS solitons can be generalized to arbitrary dimensions in our theories. In particular, we obtain the smooth AdS solitons that can be viewed as the resolution of the Reissner-Nordstrom superstars in general dimensions.Comment: Latex, 24 page

    Thermodynamics of Lifshitz Black Holes

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    We specialize the Wald formalism to derive the thermodynamical first law for static black holes with spherical/torus/hyperbolic symmetries in a variety of supergravities or supergravity-inspired theories involving multiple scalars and vectors. We apply the formula to study the first law of a general class of Lifshitz black holes. We analyse the first law of three exact Lifshitz black holes and the results fit the general pattern. In one example, the first law is TdS+ΦdQ=0TdS + \Phi dQ=0 where (Φ,Q)(\Phi,Q) are the electric potential and charge of the Maxwell field. The unusual vanishing of mass in this specific solution demonstrates that super-extremal charged black holes can exist in asymptotic Lifshitz spacetimes.Comment: 27 page

    Scalar Charges in Asymptotic AdS Geometries

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    We show that for n-dimensional Einstein gravity coupled to a scalar field with mass-squared m_0^2=-n(n-2)/(4\ell^2), the first law of thermodynamics of (charged) AdS black holes will be modified by the boundary conditions of the scalar field at asymptotic infinity. Such scalars can arise in gauged supergravities in four and six dimensions, but not in five or seven. The result provides a guiding principle for constructing designer black holes and solitons in general dimensions, where the properties of the dual field theories depend on the boundary conditions.Comment: Latex, 9 pages, references adde
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