689 research outputs found
Revisiting Multi-Step Nonlinearity Compensation with Machine Learning
For the efficient compensation of fiber nonlinearity, one of the guiding
principles appears to be: fewer steps are better and more efficient. We
challenge this assumption and show that carefully designed multi-step
approaches can lead to better performance-complexity trade-offs than their
few-step counterparts.Comment: 4 pages, 3 figures, This is a preprint of a paper submitted to the
2019 European Conference on Optical Communicatio
Coherent many-body spin dynamics in a long-range interacting Ising chain
Coherent many-body quantum dynamics lies at the heart of quantum simulation
and quantum computation. Both require coherent evolution in the exponentially
large Hilbert space of an interacting many-body system. To date, trapped ions
have defined the state of the art in terms of achievable coherence times in
interacting spin chains. Here, we establish an alternative platform by
reporting on the observation of coherent, fully interaction-driven quantum
revivals of the magnetization in Rydberg-dressed Ising spin chains of atoms
trapped in an optical lattice. We identify partial many-body revivals at up to
about ten times the characteristic time scale set by the interactions. At the
same time, single-site-resolved correlation measurements link the magnetization
dynamics with inter-spin correlations appearing at different distances during
the evolution. These results mark an enabling step towards the implementation
of Rydberg atom based quantum annealers, quantum simulations of higher
dimensional complex magnetic Hamiltonians, and itinerant long-range interacting
quantum matter.Comment: 11 pages, 9 figure
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Direct Injection Molding Tooling Inserts from the SLS Process with Copper Polyamide
The "RapidTool" Short Run (SR) Tooling Process using the Copper Polyamide
material provides a route to mold inserts for injection molding made directly in
the Selective Laser Sintering machine. The STL files for the mold inserts are
shelled and conformal cooling lines and ejector pin guides are added before SLS
processing. Sintering of the material in the SLS machine provides quick
metal/plastic tooling with good thermal conductivity. Final preparation of the
tooling inserts includes sealing the surface with epoxy, final finishing using
sandpaper, and backing up the shells with a metal alloy. The Copper Polyamide
SR Tooling inserts are used to mold several hundred parts with common plastics
with injection cycle times similar to conventional molding cycle times.Mechanical Engineerin
Invasion trajectory of Pacific oysters in the northern Wadden Sea
Invasion trajectories of introduced alien species usually begin with a long establishment phase of low abundance, often followed by exponential expansion and subsequent adjustment phases. We review the first 26 years of feral Pacific oysters Crassostrea gigas around the island of Sylt in the Wadden Sea (North Sea, NE Atlantic), and reveal causal conditions for the invasion phases. Sea-based oyster farming with repeated introductions made establishment of feral oysters almost inevitable. Beds of mussels Mytilus edulis on mud flats offered firm substrate for attachment and ideal growth conditions around low tide level. C. gigas mapped on to the spatial pattern of mussel beds. During the 1990s, cold summers often hampered recruitment and abundances remained low but oyster longevity secured persistence. Since the 2000s, summers were often warmer and recruitment more regular. Young oysters attached to adult oysters and abundances of >1000 m−2 were achieved. However, peak abundance was followed by recruitment failure. The population declined and then was
also struck by ice winters causing high mortality. Recovery was fast (>2000 m−2) but then recruitment failed again. We expect adjustment phase will proceed with mean abundance of about 1000 m−2 but density-dependent (e.g., diseases) and density-independent (e.g., weather anomalies) events causing strong fluctuations. With continued global warming, feral C. gigas at the current invasion fronts in British estuaries and Scandinavian fjords may show similar adjustment trajectories as observed in the northern Wadden Sea, and also other marine introductions may follow the invasion trajectory of Pacific oysters
Effect of strobilurin fungicides on control of early blight (Alternaria solani) and yield of potatoes grown under two N fertility regimes
Early blight, caused by Alternaria solani, is a ubiquitous disease that can reduce potato yield. Adequate crop fertility and appropriate fungicide applications usually suppress the development of this disease. Field trials were established in Prince Edward Island to determine whether strobilurin analogs, namely azoxystrobin and pyraclostrobin, could suppress early blight of potatoes (cvs. Shepody and Russet Burbank) grown under two nitrogen (N) fertility regimes (high or low N). Azoxystrobin and pyraclostrobin were linked to significantly higher total tuber yield for Russet Burbank in 2003 and Shepody in 2004 when compared to plots receiving no strobilurin fungicides. No significant differences in total tuber yield based on N fertility were observed, although the high N rate decreased disease in Russet Burbank control plots in 2004. Due to an absence of early blight in 2003, the increase in Russet Burbank yield may be attributed to the physiological and developmental alterations brought about by strobilurin products in treated plants. In 2004, early blight was severe in inoculated control plots, but it was significantly suppressed in plots having received azoxystrobin or pyraclostrobin, regardless of the cultivar type or fertility regime. Therefore, to prevent unnecessary N inputs, growers need to supply only the necessary N amount to optimize tuber yields and manage early blight with fungicides.L’alternariose, causée par Alternaria solani, est une maladie omniprésente qui peut réduire le rendement de la pomme de terre. Une fertilisation adéquate de la culture et l’application de fongicides appropriés suppriment généralement le développement de cette maladie. Des essais en champs ont été effectués à l’Île-du-Prince-Édouard pour déterminer si des analogues de la strobilurine, notamment l’azoxystrobine et la pyraclostrobine, pouvaient supprimer l’alternariose de la pomme de terre (cv. Shepody et Russet Burbank) cultivée sous deux régimes de fertilité azotée (forte et faible doses de N). L’azoxystrobine et la pyraclostrobine ont été associées au rendement total en tubercules significativement supérieur pour Russet Burbank en 2003 et pour Shepody en 2004, comparativement à des parcelles n’ayant reçu aucun fongicide apparenté à la strobilurine. La fertilité azotée n’a entraîné aucune différence significative du rendement, bien que la dose élevée d’azote ait significativement réduit la maladie dans les parcelles témoins de Russet Burbank en 2004. En raison de l’absence de l’alternariose en 2003, l’augmentation du rendement du cv. Russet Burbank peut être attribuée aux modifications causées par les produits de la strobilurine dans la physiologie et le développement des plantes traitées. En 2004, l’alternariose a été importante dans les parcelles témoins inoculées, mais la suppression a été significative dans les parcelles ayant reçu de l’azoxystrobine ou de la pyraclostrobine, quels que soient le cultivar ou le régime de fertilité. Ainsi, les producteurs devraient appliquer uniquement les quantités d’azote nécessaires pour optimiser les rendements en tubercules et contrôler l’alternariose avec des fongicides
Entanglement Hamiltonian Tomography in Quantum Simulation
Entanglement is the crucial ingredient of quantum many-body physics, and
characterizing and quantifying entanglement in closed system dynamics of
quantum simulators is an outstanding challenge in today's era of intermediate
scale quantum devices. Here we discuss an efficient tomographic protocol for
reconstructing reduced density matrices and entanglement spectra for spin
systems. The key step is a parametrization of the reduced density matrix in
terms of an entanglement Hamiltonian involving only quasi local few-body terms.
This ansatz is fitted to, and can be independently verified from, a small
number of randomised measurements. The ansatz is suggested by Conformal Field
Theory in quench dynamics, and via the Bisognano-Wichmann theorem for ground
states. Not only does the protocol provide a testbed for these theories in
quantum simulators, it is also applicable outside these regimes. We show the
validity and efficiency of the protocol for a long-range Ising model in 1D
using numerical simulations. Furthermore, by analyzing data from and
ion quantum simulators [Brydges \textit{et al.}, Science, 2019], we demonstrate
measurement of the evolution of the entanglement spectrum in quench dynamics.Comment: 13 pages (6 pages supplemental information), 9 figure
Model-Based Machine Learning for Joint Digital Backpropagation and PMD Compensation
In this paper, we propose a model-based machine-learning approach for
dual-polarization systems by parameterizing the split-step Fourier method for
the Manakov-PMD equation. The resulting method combines hardware-friendly
time-domain nonlinearity mitigation via the recently proposed learned digital
backpropagation (LDBP) with distributed compensation of polarization-mode
dispersion (PMD). We refer to the resulting approach as LDBP-PMD. We train
LDBP-PMD on multiple PMD realizations and show that it converges within 1% of
its peak dB performance after 428 training iterations on average, yielding a
peak effective signal-to-noise ratio of only 0.30 dB below the PMD-free case.
Similar to state-of-the-art lumped PMD compensation algorithms in practical
systems, our approach does not assume any knowledge about the particular PMD
realization along the link, nor any knowledge about the total accumulated PMD.
This is a significant improvement compared to prior work on distributed PMD
compensation, where knowledge about the accumulated PMD is typically assumed.
We also compare different parameterization choices in terms of performance,
complexity, and convergence behavior. Lastly, we demonstrate that the learned
models can be successfully retrained after an abrupt change of the PMD
realization along the fiber.Comment: 10 pages, 11 figures, to appear in the IEEE/OSA Journal of Lightwave
Technolog
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