Theoretische Physik, LMU München

In quantum information theory, entangled states of multi-partite systems play the role of a central resource for information processing. Examples of such states are given by certain quantum error correcting codes, GHZ states and cluster states, which have applications in both quantum communication and computation. For fundamental and practical reasons, it is essential that these fragile states can be protected against the detrimental effects of decoherence and noise, in particular when the size of the quantum systems grows large. In the main part of this talk, I will describe a novel protocol of entanglement purification [1] which allows one to purify a large number multi-party entanglement states, including the examples given above. More generally, the class of multi-qubit states that can be purified under the protocol can be associated with 2-colorable graphs.

[1] Duer, Aschauer, Briegel "Multiparticle entanglement purification for graph states", quant-ph/0303087.