6,827 research outputs found
Enhanced current noise correlations in a Coulomb-Majorana device
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
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
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
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
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
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
where 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
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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