Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a One-Dimensional Trap

We report on the deterministic preparation of antiferromagnetic Heisenberg spin chains consisting of up to four fermionic atoms in a one-dimensional trap. These chains are stabilized by strong repulsive interactions between the two spin components without the need for an external periodic potential. We independently characterize the spin configuration of the chains by measuring the spin orientation of the outermost particle in the trap and by projecting the spatial wave function of one spin component on single-particle trap levels. Our results are in good agreement with a spin-chain model for fermionized particles and with numerically exact diagonalizations of the full few-fermion system

Galileo ionospheric correction algorithm: an optimization study of NeQuick-G

At present most low-cost GNSS receivers operate one frequency in the L band. For themone of the largest error contributions is the delay of radio signals in the Ionosphere. NeQuick-Gisthe official ionospheric correction algorithm (ICA), which has been adopted for Galileo, the EuropeanGNSS Programme. The NeQuick-G implementation is complex when compared with other ICAs. Itis also demanding in terms of computational resources. The Joint Research Centre completed areference implementation of NeQuick-G based on the official document“Ionospheric CorrectionAlgorithm for Galileo Single Frequency Users”provided by the European Global Navigation SatelliteSystems Agency. The rationale behind the JRC implementation of NeQuick-G was the intent to write anindependent source code from scratch, without using the pseudo-codes from the reference documentand solely relying on the physics descriptions. Using such implementation as baseline, this paperdescribes an optimization attempt of the official pseudo-code from an algorithmic perspective. Theobjective was to reduce the computational load while not sacrificing the performance. The newproposed integration method is able to speed up calculations to 21% and 49% with respect the twoofficial integration algorithms. The overall computational burden depends on the number of operations,which is eventually closely correlated to the number of calls of the ionospheric model. This underlinesthe quest tofind an integration method reducing this number of calls. Moreover, based on thefindings of this study, the authors strongly recommend revisiting the convergence control of theintegration routines introduced in (European Commission, 2016, https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_Ionospheric_Model.pdf).Peer ReviewedPostprint (published version

Fermionization of two distinguishable fermions

In this work we study a system of two distinguishable fermions in a 1D harmonic potential. This system has the exceptional property that there is an analytic solution for arbitrary values of the interparticle interaction. We tune the interaction strength via a magnetic offset field and compare the measured properties of the system to the theoretical prediction. At the point where the interaction strength diverges, the energy and square of the wave function for two distinguishable particles are the same as for a system of two identical fermions. This is referred to as fermionization. We have observed this phenomenon by directly comparing two distinguishable fermions with diverging interaction strength with two identical fermions in the same potential. We observe good agreement between experiment and theory. By adding one or more particles our system can be used as a quantum simulator for more complex few-body systems where no theoretical solution is available

Line narrowing and spectral hole burning in single mode Nd³⁺- fibre lasers

Line-narrowing in the output spectrum of an Nd-doped silica-fiber laser with spectrally flat reflectors is interpreted to indicate substantial homogenous contribution to the 1.09µm fluorescent linewidth. Using a fiber Bragg-reflector, frequency-stable operation with 100GHz bandwidth is obtained, dominated by power broadening and spectral hole burning

International organisations and human rights: What direct authority needs for its legitimation

The Institutions of Politics; Design, Workings, and implications ( do not use, ended 1-1-2020