1112.1355 (Fu-Guo Deng)

Optimal nonlocal multipartite entanglement concentration based on
projection measurements    [PDF]

Fu-Guo Deng

We propose an optimal nonlocal entanglement concentration protocol (ECP) for
multi-photon systems in a partially entangled pure state, resorting to the
projection measurement on an additional photon. One party in quantum
communication first performs a parity-check measurement on her photon in an
N-photon system and an additional photon, and then she projects the additional
photon into an orthogonal Hilbert space for dividing the original $N$-photon
systems into two groups. In the first group, the N parties will obtain a subset
of $N$-photon systems in a maximally entangled state. In the second group, they
will obtain some less-entangled N-photon systems which are the resource for the
entanglement concentration in the next round. By iterating the entanglement
concentration process several times, the present ECP has the maximal success
probability which is just equivalent to the entanglement of the partially
entangled state. That is, this ECP is an optimal one.

View original: http://arxiv.org/abs/1112.1355