A quantitative witness for Greenberger-Horne-Zeilinger entanglement

Along with the vast progress in experimental quantum technologies there is an increasing demand for the quantification of entanglement between three or more quantum systems. Theory still does not provide adequate tools for this purpose. The objective is, besides the quest for exact results, to develop operational methods that allow for efficient entanglement quantification. Here we put forward an analytical approach that serves both these goals. We provide a simple procedure to quantify Greenberger-Horne-Zeilinger-type multipartite entanglement in arbitrary three-qubit states. For two qubits this method is equivalent to Wootters' seminal result for the concurrence. It establishes a close link between entanglement quantification and entanglement detection by witnesses, and can be generalised both to higher dimensions and to more than three parties.

Dual-path methods for propagating quantum microwaves

We study quantum state tomography, entanglement detection and channel noise reconstruction of propagating quantum microwaves via dual-path methods. The presented schemes make use of the following key elements: propagation channels, beam splitters, linear amplifiers and field quadrature detectors. Remarkably, our methods are tolerant to the ubiquitous noise added to the signals by phase-insensitive microwave amplifiers. Furthermore, we analyse our techniques with numerical examples and experimental data, and compare them with the scheme developed in Eichler et al (2011 Phys. Rev. Lett. 106 220503; 2011 Phys. Rev. Lett. 107 113601), based on a single path. Our methods provide key toolbox components that may pave the way towards quantum microwave teleportation and communication protocols.

Irakurketaren onurak eta irakurzaletasuna sustatzeko jarduera eraginkorrak

Laburpena. Lan honek irakurzaletasunak eskola haurrari eskaintzen dizkion onurak zeintzuk diren zehazten du, eta azken urteotan eskoletan irakurzaletasuna sustatzeko gauzatu izan diren jarduera eraginkorrenetariko batzuk aurkezten ditu. Erabili izan den metodologia bilaketa bibliografiko sakon batean oinarrituta dago, hemen aipatzen den ekintza eraginkor bakoitzak izandako emaitzak kualitatiboki nahiz kuantitatiboki frogatuta daudelarik. Lanak hainbat muga dauzka, oso zaila delako egin diren ekintzen jarraipenen zifrak lortzea; horregatik, eraginkorrak diren beste hainbat ekintza egongo dira hemen aipatzen ez direnak datu faltagatik. Hala ere, ikerketa interesgarria da irakurzaletasunak dakartzan onurak frogatzen dituezten adituen testigantzak biltzen dituelako eta emaitza onak lortu dituzten ekintzak soilik aurkezten dituelako.