772 research outputs found
Phase transition in site-diluted Josephson junction arrays: A numerical study
We numerically investigate the intriguing effects produced by random
percolative disorder in two-dimensional Josephson-junction arrays. By dynamic
scaling analysis, we evaluate critical temperatures and critical exponents with
high accuracy. It is observed that, with the introduction of site-diluted
disorder, the Kosterlitz-Thouless phase transition is eliminated and evolves
into a continuous transition with power-law divergent correlation length.
Moreover, genuine depinning transition and creep motion are studied, evidence
for distinct creep motion types is provided. Our results not only are in good
agreement with the recent experimental findings, but also shed some light on
the relevant phase transitions.Comment: 7 pages, 8 figures, Phys. Rev. B (in press
Dynamics of glass phases in the two-dimensional gauge glass model
Large-scale simulations have been performed on the current-driven
two-dimensional XY gauge glass model with resistively-shunted-junction
dynamics. It is observed that the linear resistivity at low temperatures tends
to zero, providing strong evidence of glass transition at finite temperature.
Dynamic scaling analysis demonstrates that perfect collapses of current-voltage
data can be achieved with the glass transition temperature , the
correlation length critical exponent , and the dynamic critical
exponent . A genuine continuous depinning transition is found at zero
temperature. For creeping at low temperatures, critical exponents are evaluated
and a non-Arrhenius creep motion is observed in the glass phase.Comment: 10 pages, 6 figure
Rethinking the Up-Sampling Operations in CNN-based Generative Network for Generalizable Deepfake Detection
Recently, the proliferation of highly realistic synthetic images, facilitated
through a variety of GANs and Diffusions, has significantly heightened the
susceptibility to misuse. While the primary focus of deepfake detection has
traditionally centered on the design of detection algorithms, an investigative
inquiry into the generator architectures has remained conspicuously absent in
recent years. This paper contributes to this lacuna by rethinking the
architectures of CNN-based generators, thereby establishing a generalized
representation of synthetic artifacts. Our findings illuminate that the
up-sampling operator can, beyond frequency-based artifacts, produce generalized
forgery artifacts. In particular, the local interdependence among image pixels
caused by upsampling operators is significantly demonstrated in synthetic
images generated by GAN or diffusion. Building upon this observation, we
introduce the concept of Neighboring Pixel Relationships(NPR) as a means to
capture and characterize the generalized structural artifacts stemming from
up-sampling operations. A comprehensive analysis is conducted on an open-world
dataset, comprising samples generated by \tft{28 distinct generative models}.
This analysis culminates in the establishment of a novel state-of-the-art
performance, showcasing a remarkable \tft{11.6\%} improvement over existing
methods. The code is available at
https://github.com/chuangchuangtan/NPR-DeepfakeDetection.Comment: 10 pages, 4 figure
Can Variational Quantum Algorithms Demonstrate Quantum Advantages? Time Really Matters
Applying low-depth quantum neural networks (QNNs), variational quantum
algorithms (VQAs) are both promising and challenging in the noisy
intermediate-scale quantum (NISQ) era: Despite its remarkable progress,
criticisms on the efficiency and feasibility issues never stopped. However,
whether VQAs can demonstrate quantum advantages is still undetermined till now,
which will be investigated in this paper. First, we will prove that there
exists a dependency between the parameter number and the gradient-evaluation
cost when training QNNs. Noticing there is no such direct dependency when
training classical neural networks with the backpropagation algorithm, we argue
that such a dependency limits the scalability of VQAs. Second, we estimate the
time for running VQAs in ideal cases, i.e., without considering realistic
limitations like noise and reachability. We will show that the ideal time cost
easily reaches the order of a 1-year wall time. Third, by comparing with the
time cost using classical simulation of quantum circuits, we will show that
VQAs can only outperform the classical simulation case when the time cost
reaches the scaling of - years. Finally, based on the above
results, we argue that it would be difficult for VQAs to outperform classical
cases in view of time scaling, and therefore, demonstrate quantum advantages,
with the current workflow. Since VQAs as well as quantum computing are
developing rapidly, this work does not aim to deny the potential of VQAs. The
analysis in this paper provides directions for optimizing VQAs, and in the long
run, seeking more natural hybrid quantum-classical algorithms would be
meaningful.Comment: 18 pages, 7 figure
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