Multiparticle entanglement purification for two-colorable graph states (20 pages)

H. J. Briegel, M. Hein, Jens Eisert

A. N. Salgueiro

Hans Aschauer, Wolfgang Dür, Hans J. Briegel

We investigate multiparticle entanglement purification schemes which allow one to purify all two colorable graph states, a class of states which includes, e.g., cluster states, Greenberger-Horne-Zeilinger states, and code words of various error correction codes. The schemes include both recurrence protocols and hashing protocols. We analyze these schemes under realistic conditions and observe for a generic error model that the threshold value for imperfect local operations depends on the structure of the corresponding interaction graph, but is otherwise independent of the number of parties. The qualitative behavior can be understood from an analytically solvable model which deals only with a restricted class of errors. We compare direct multiparticle entanglement purification protocols with schemes based on bipartite entanglement purification and show that the direct multiparticle entanglement purification is more efficient and the achievable fidelity of the purified states is larger. We also show that the purification protocol allows one to produce private entanglement, an important aspect when using the produced entangled states for secure applications. Finally we discuss an experimental realization of a multiparty purification protocol in optical lattices which is issued to improve the fidelity of cluster states created in such systems.

Junyi WU

Wolfgang Dür, Harald N. Aschauer, Hans J. Briegel

We introduce a class of multiparticle entanglement purification protocols that allow us to distill a large class of entangled states. These include cluster states, Greenberger-Horne-Zeilinger states, and various error correction codes all of which belong to the class of two-colorable graph states. We analyze these schemes under realistic conditions and observe that they are scalable; i.e., the threshold value for imperfect local operations does not depend on the number of parties for many of these states. When compared to schemes based on bipartite entanglement purification, the protocol is more efficient and the achievable quality of the purified states is larger. As an application we discuss an experimental realization of the protocol in optical lattices which allows one to purify cluster states.

Mio Murao, Martin Bodo Plenio, Sandu Popescu +2 more

Purification schemes for multiparticle entangled states cannot be treated as straightforward extensions of those two-particle ones because of the lack of symmetry they possess. We propose purification protocols for a wide range of mixed entangled states of many particles. These are useful for understanding entanglement, and could be of practical significance in multiuser cryptographic schemes or distributed quantum computation and communication. We show that operating locally on multiparticle entangled states directly is more efficient than relying on two-particle purification.