2,906 research outputs found
Estimating entanglement monotones with a generalization of the Wootters formula
Entanglement monotones, such as the concurrence, are useful tools to
characterize quantum correlations in various physical systems. The computation
of the concurrence involves, however, difficult optimizations and only for the
simplest case of two qubits a closed formula was found by Wootters [Phys. Rev.
Lett. 80, 2245 (1998)]. We show how this approach can be generalized, resulting
in lower bounds on the concurrence for higher dimensional systems as well as
for multipartite systems. We demonstrate that for certain families of states
our results constitute the strongest bipartite entanglement criterion so far;
moreover, they allow to recognize novel families of multiparticle bound
entangled states.Comment: 8 pages, one figure, v2: small change
Low-Light Enhancement in the Frequency Domain
Decreased visibility, intensive noise, and biased color are the common
problems existing in low-light images. These visual disturbances further reduce
the performance of high-level vision tasks, such as object detection, and
tracking. To address this issue, some image enhancement methods have been
proposed to increase the image contrast. However, most of them are implemented
only in the spatial domain, which can be severely influenced by noise signals
while enhancing. Hence, in this work, we propose a novel residual recurrent
multi-wavelet convolutional neural network R2-MWCNN learned in the frequency
domain that can simultaneously increase the image contrast and reduce noise
signals well. This end-to-end trainable network utilizes a multi-level discrete
wavelet transform to divide input feature maps into distinct frequencies,
resulting in a better denoise impact. A channel-wise loss function is proposed
to correct the color distortion for more realistic results. Extensive
experiments demonstrate that our proposed R2-MWCNN outperforms the
state-of-the-art methods quantitively and qualitatively.Comment: 8 page
Improved lower bounds on genuine-multipartite-entanglement concurrence
Genuine-multipartite-entanglement (GME) concurrence is a measure of genuine
multipartite entanglement that generalizes the well-known notion of
concurrence. We define an observable for GME concurrence. The observable
permits us to avoid full state tomography and leads to different analytic lower
bounds. By means of explicit examples we show that entanglement criteria based
on the bounds have a better performance with respect to the known methods.Comment: 17 pages, 1 EPS figure; v3 is in one column to improve readability of
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