Sascha Gaertner

TL;DR: A canonical way of constructing and decomposing witness operators so that they can be directly implemented with present technology is introduced and applied to three- and four-qubit entangled states of polarized photons, giving experimental evidence that the considered states contain true multipartite entanglement.

TL;DR: It is demonstrated 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 and the immunity against noise is verified by quantum state tomography of the encoded qubit.

TL;DR: 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 multiparty quantum key distribution, secret sharing, and telecloning.

TL;DR: This work presents an experimental demonstration of four-party quantum secret sharing via the resource ofFour-photon entanglement, a multiparty cryptographic task in which some secret information is split into several pieces which are distributed among the participants such that only an authorized set of participants can reconstruct the original secret.

TL;DR: A new quantum protocol for solving detectable Byzantine agreement (also called detectable broadcast) between three parties, and also for solving the detectable liar detection problem, is introduced.