University of Paderborn

About: University of Paderborn is a education organization based out in Paderborn, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Control reconfiguration & Software. The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

Photon Temporal Modes: A Complete Framework for Quantum Information Science

Abstract: Because photons interact weakly with themselves and experience low decoherence, they are a promising avenue for quantum information science. Theorists show how the temporal modes of single-photon states can form an alphabet for communication across a quantum information network.

How far do chemotaxis-driven forces influence regularity in the Navier-Stokes system?

Abstract: The chemotaxis-Navier-Stokes system    nt + u · ∇n = ∆n−∇ · (nχ(c)∇c), ct + u · ∇c = ∆c− nf(c), ut + (u · ∇)u = ∆u+∇P + n∇Φ, ∇ · u = 0, (⋆) (0.1) is considered under boundary conditions of homogeneous Neumann type for n and c, and Dirichlet type for u, in a bounded convex domain Ω ⊂ R with smooth boundary, where Φ ∈ W (Ω) and χ and f are sufficiently smooth given functions generalizing the prototypes χ ≡ const. and f(s) = s for s ≥ 0. It is known that for all suitably regular initial data n0, c0 and u0 satisfying 0 6≡ n0 ≥ 0, c0 ≥ 0 and ∇ · u0 = 0, a corresponding initial-boundary value problem admits at least one global weak solution which can be obtained as the pointwise limit of a sequence of solutions to appropriately regularized problems. The present paper shows that after some relaxation time, this solution enjoys further regularity properties and thereby complies with the concept of eventual energy solutions which is newly introduced here, and which inter alia requires that two quasi-dissipative inequalities are ultimately satisfied. Moreover, it is shown that actually for any such eventual energy solution (n, c, u) there exists a waiting time T0 ∈ (0,∞) with the property that (n, c, u) is smooth in Ω× [T0,∞), and that n(x, t) → n0, c(x, t) → 0 and u(x, t) → 0 hold as t → ∞, uniformly with respect to x ∈ Ω. This resembles a classical result on the three-dimensional Navier-Stokes system, asserting eventual smoothness of arbitrary weak solutions thereof which additionally fulfill the associated natural energy inequality. In consequence, our results inter alia indicate that under the considered boundary conditions, the possibly destabilizing action of chemotactic cross-diffusion in (⋆) does not substantially affect the regularity properties of the fluid flow at least on large time scales.

Optimal oblivious routing in polynomial time

Abstract: A recent seminal result of Racke is that for any network there is an oblivious routing algorithm with a polylog competitive ratio with respect to congestion. Unfortunately, Racke's construction is not polynomial time. We give a polynomial time construction that guarantee's Racke's bounds, and more generally gives the true optimal ratio for any network.

Highly directional emission from photonic crystal waveguides of subwavelength width.

Abstract: Recently it has been shown that it is possible to achieve directional emission out of a subwavelength aperture in a periodically corrugated metallic thin film. We report on theoretical and experimental studies of a related phenomenon concerning light emitted from photonic crystal waveguides that are less than a wavelength wide. We find that the termination of the photonic crystal end facets and an appropriate choice of the wavelength are instrumental in achieving very low numerical apertures. Our results hold promise for the combination of photonic crystal waveguides with conventional optical systems such as fibers, waveguides, and freely propagating light beams.

Metasurface holography: from fundamentals to applications

Abstract: Holography has emerged as a vital approach to fully engineer the wavefronts of light since its invention dating back to the last century. However, the typically large pixel size, small field of view and limited space-bandwidth impose limitations in the on-demand high-performance applications, especially for three-dimensional displays and large-capacity data storage. Meanwhile, metasurfaces have shown great potential in controlling the propagation of light through the well-tailored scattering behavior of the constituent ultrathin planar elements with a high spatial resolution, making them suitable for holographic beam-shaping elements. Here, we review recent developments in the field of metasurface holography, from the classification of metasurfaces to the design strategies for both free-space and surface waves. By employing the concepts of holographic multiplexing, multiple information channels, such as wavelength, polarization state, spatial position and nonlinear frequency conversion, can be employed using metasurfaces. Meanwhile, the switchable metasurface holography by the integration of functional materials stimulates a gradual transition from passive to active elements. Importantly, the holography principle has become a universal and simple approach to solving inverse engineering problems for electromagnetic waves, thus allowing various related techniques to be achieved.