# Berlin 2014 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 37: Quantum information: Concepts and methods I

### Q 37.6: Vortrag

### Donnerstag, 20. März 2014, 11:45–12:00, Kinosaal

**Analytic expressions for the genuine multiparticle negativity** — •Martin Hofmann, Tobias Moroder, and Otfried Gühne — Theoretical Quantum Optics, University of Siegen, Siegen, Germany

Entanglement is considered a very useful resource in quantum information. It is involved in some quantum key distribution protocols, quantum metrology, quantum phase transitions and many other physical applications and phenomena. To gain new insights the detection and quantification of entangled states turned out to be very helpful.

In systems with more than two parties the entangled states itself yield an interesting substructure making it more challenging to to detect and quantify entangled states in these subsets. For bipartite mixed states there is essentially only one computable entanglement monotone. That is the bipartite negativity.

In our work we investigate a slightly modified version of the genuine multiparticle negativity, which was introduced in Ref. [1]. That is a computable mixed state monotone detecting genuine multiparticle entanglement. Although it can not detect all genuine multiparticle entangled states it turns out to work quite good in practice. We show that two equivalent definitions of this monotone yield naturally arising upper and lower bounds. These can be used to derive exact analytic expressions for the modified genuine multiparticle negativity for *n*-qubit GHZ diagonal and four-qubit cluster diagonal states. These formulas are necessary and sufficient to fully characterize the set of genuine multiparticle entangled states within both families.

[1] B. Jungnitsch et al., Phys. Rev. Lett. 106, 190502 (2011).