MULTIPARTICLE ENTANGLEMENT PURIFICATION PROTOCOLS

Purification schemes for multiparticle entangled states cannot be trea ted as straightforward extensions of those two-particle ones because o f the lack of symmetry they possess. We propose purification protocols for a wide range of mixed entangled states of many particles. These a re useful for understanding entanglement, and could be of practical si gnificance in multiuser cryptographic schemes or distributed quantum c omputation and communication. We show that operating locally on multip article entangled states directly is more efficient than relying on tw o-particle purification.