# QIS

## Seminar

### Graph states - stability under decoherence, entanglement purification and possible applications

Seminar Room 2, Newton Institute Gatehouse

#### Abstract

We will consider a specific family of multipartite entangled states, namely (weighted) graph states. We investigate the influence of decoherence on the entanglement properties of the states for various decoherence models. We show that the lifetime of entanglement of GHZ states decreases with the number of particles, while cluster (and similar) graph states the lifetime is independent of the size of the system. We discuss several multiparty entanglement purification protocols which allow one to create and/or maintain two colorable graph states with high fidelity. We compare direct multiparty entanglement purification protocols with protocols based on bipartite purification and show that the former are more efficient. We investigate the influence of imperfections in local control operations, where we find a remarkable robustness against errors for protocols which allow one, e.g., to purify cluster states. The achievable fidelity using direct multiparty purification is higher than purification based on bipartite protocols. We discuss possible applications of multiparty entanglement purification protocols for secure multiparty communication.