3,044 research outputs found
Concise Security Bounds for Practical Decoy-State Quantum Key Distribution
Due to its ability to tolerate high channel loss, decoy-state quantum key
distribution (QKD) has been one of the main focuses within the QKD community.
Notably, several experimental groups have demonstrated that it is secure and
feasible under real-world conditions. Crucially, however, the security and
feasibility claims made by most of these experiments were obtained under the
assumption that the eavesdropper is restricted to particular types of attacks
or that the finite-key effects are neglected. Unfortunately, such assumptions
are not possible to guarantee in practice. In this work, we provide concise and
tight finite-key security bounds for practical decoy-state QKD that are valid
against general attacks.Comment: 5+3 pages and 2 figure
Loss-tolerant quantum secure positioning with weak laser sources
Quantum position verification (QPV) is the art of verifying the geographical
location of an untrusted party. Recently, it has been shown that the widely
studied Bennett & Brassard 1984 (BB84) QPV protocol is insecure after the 3 dB
loss point assuming local operations and classical communication (LOCC)
adversaries. Here, we propose a time-reversed entanglement swapping QPV
protocol (based on measurement-device-independent quantum cryptography) that is
highly robust against quantum channel loss. First, assuming ideal qubit
sources, we show that the protocol is secure against LOCC adversaries for any
quantum channel loss, thereby overcoming the 3 dB loss limit. Then, we analyze
the security of the protocol in a more practical setting involving weak laser
sources and linear optics. In this setting, we find that the security only
degrades by an additive constant and the protocol is able to verify positions
up to 47 dB channel loss.Comment: 11 pages, 3 figures. Partially based on an earlier work in
arXiv:1510.0489
Accelerating Backward Aggregation in GCN Training with Execution Path Preparing on GPUs
The emerging Graph Convolutional Network (GCN) has now been widely used in
many domains, and it is challenging to improve the efficiencies of applications
by accelerating the GCN trainings. For the sparsity nature and exploding scales
of input real-world graphs, state-of-the-art GCN training systems (e.g.,
GNNAdvisor) employ graph processing techniques to accelerate the message
exchanging (i.e. aggregations) among the graph vertices. Nevertheless, these
systems treat both the aggregation stages of forward and backward propagation
phases as all-active graph processing procedures that indiscriminately conduct
computation on all vertices of an input graph.
In this paper, we first point out that in a GCN training problem with a given
training set, the aggregation stages of its backward propagation phase (called
as backward aggregations in this paper) can be converted to partially-active
graph processing procedures, which conduct computation on only partial vertices
of the input graph. By leveraging such a finding, we propose an execution path
preparing method that collects and coalesces the data used during backward
propagations of GCN training conducted on GPUs. The experimental results show
that compared with GNNAdvisor, our approach improves the performance of the
backward aggregation of GCN trainings on typical real-world graphs by
1.48x~5.65x. Moreover, the execution path preparing can be conducted either
before the training (during preprocessing) or on-the-fly with the training.
When used during preprocessing, our approach improves the overall GCN training
by 1.05x~1.37x. And when used on-the-fly, our approach improves the overall GCN
training by 1.03x~1.35x
Soil phosphorus heterogeneity promotes tree species diversity and phylogenetic clustering in a tropical seasonal rainforest
The niche theory predicts that environmental heterogeneity and species diversity are positively correlated in tropical forests, whereas the neutral theory suggests that stochastic processes are more important in determining species diversity. This study sought to investigate the effects of soil nutrient (nitrogen and phosphorus) heterogeneity on tree species diversity in the Xishuangbanna tropical seasonal rainforest in southwestern China. Thirty-nine plots of 400 m2 (20 × 20 m) were randomly located in the Xishuangbanna tropical seasonal rainforest. Within each plot, soil nutrient (nitrogen and phosphorus) availability and heterogeneity, tree species diversity, and community phylogenetic structure were measured. Soil phosphorus heterogeneity and tree species diversity in each plot were positively correlated, while phosphorus availability and tree species diversity were not. The trees in plots with low soil phosphorus heterogeneity were phylogenetically overdispersed, while the phylogenetic structure of trees within the plots became clustered as heterogeneity increased. Neither nitrogen availability nor its heterogeneity was correlated to tree species diversity or the phylogenetic structure of trees within the plots. The interspecific competition in the forest plots with low soil phosphorus heterogeneity could lead to an overdispersed community. However, as heterogeneity increase, more closely related species may be able to coexist together and lead to a clustered community. Our results indicate that soil phosphorus heterogeneity significantly affects tree diversity in the Xishuangbanna tropical seasonal rainforest, suggesting that deterministic processes are dominant in this tropical forest assembly
Hopping Conduction in Disordered Carbon Nanotubes
We report electrical transport measurements on individual disordered carbon
nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template.
In both as-grown and annealed types of nanotubes, the low-field conductance
shows as exp[-(T_{0}/T)^{1/2}] dependence on temperature T, suggesting that
hopping conduction is the dominant transport mechanism, albeit with different
disorder-related coefficients T_{0}. The field dependence of low-temperature
conductance behaves an exp[-(xi_{0}/xi)^{1/2}] with high electric field xi at
sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit
weak positive magnetoresistance at low T = 1.7 K. Comparison with theory
indicates that our data are best explained by Coulomb-gap variable range
hopping conduction and permits the extraction of disorder-dependent
localization length and dielectric constant.Comment: 10 pages, 5 figure
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