Addendum to "Experimental demonstration of a quantum protocol for Byzantine agreement and liar detection" arXiv:0710.0290

Gao et al. [Phys. Rev. Lett. 101, 208901 (2008)] have described a possible intercept-resend attack for the quantum protocol for detectable Byzantine agreement in Phys. Rev. Lett. 100, 070504 (2008). Here we describe an extension of the protocol which defeats such attacks.Comment: REVTeX4, 2 page

Experimental observation of four-photon entanglement from down-conversion

We observe polarization-entanglement between four photons produced from a single down-conversion source. The non-classical correlations between the measurement results violate a generalized Bell inequality for four qubits. The characteristic properties and its easy generation with high interferometric contrast make the observed four-photon state well-suited for implementing advanced quantum communication schemes such as multi-party quantum key distribution, secret sharing and telecloning.Comment: 4 pages, 3 figure

Decoherence-Free Quantum Information Processing with Four-Photon Entangled States

Decoherence-free states protect quantum information from collective noise, the predominant cause of decoherence in current implementations of quantum communication and computation. Here we demonstrate that spontaneous parametric down-conversion can be used to generate four-photon states which enable the encoding of one qubit in a decoherence-free subspace. The immunity against noise is verified by quantum state tomography of the encoded qubit. We show that particular states of the encoded qubit can be distinguished by local measurements on the four photons only.Comment: 4 pages, 4 eps figures, revtex

Witnessing multipartite entanglement

We present the experimental detection of genuine multipartite entanglement using entanglement witness operators. To this aim we introduce a canonical way of constructing and decomposing witness operators so that they can be directly implemented with present technology. We apply this method to three- and four-qubit entangled states of polarized photons, giving experimental evidence that the considered states contain true multipartite entanglement.Comment: 4 pages, 2 figure

Friedrich Wilhelm Murnau : Bibliografie

Das folgende Verzeichnis basiert auf der Bibliographie, die anläßlich der Murnau-Retrospektive auf der Berlinale 2003 entstand und in dem Band Friedrich Wilhelm Murnau. Ein Melancholiker des Films (hrsg. v. Hans Helmut Prinzler. Berlin: Bertz 2003, S. 267-290) abgedruckt wurde. Wir danken der Stiftung Deutsche Kinemathek dafür, dass sie es ermöglichte, das Verzeichnis auch online zugänglich zu machen. Das ursprüngliche Verzeichnis wurde von Ansgar Schlichter an diversen Stellen erweitert und aktualisiert; die unterschiedlichen Formate der bibliographischen Aufnahme wurden in Kauf genommen. Ebenso beibehalten wurde die sachliche Gliederung des Verzeichnisses

Experimental demonstration of a quantum protocol for byzantine agreement and liar detection

10.1103/PhysRevLett.100.070504Physical Review Letters1007-PRLT