摘要
We present a scheme for locally concentrating a non-maximally entangled four-photon cluster state into a maximally-entangled four-photon cluster state. This scheme has a high success probability. The controlled-NOT （CNOT） gate is a crucial ingredient in this scheme, and we use a nearly deterministic CNOT gate, which is similar with that first introduced by Nemoto et al. （Phgs. Rev. Lett., 2004, 93： 250502）. This CNOT gate has a simple structure and does not need the strong nonlinearity.
We present a scheme for locally concentrating a non-maximally entangled four-photon cluster state into a maximally-entangled four-photon cluster state. This scheme has a high success probability. The controlled-NOT （CNOT） gate is a crucial ingredient in this scheme, and we use a nearly deterministic CNOT gate, which is similar with that first introduced by Nemoto et al. （Phgs. Rev. Lett., 2004, 93： 250502）. This CNOT gate has a simple structure and does not need the strong nonlinearity.
基金
Acknowledgements This work was supported by the Major Research Plan of the National Natural Science Foundation of China （Grant No. 91121023）, the National Natural Science Foundation of China （Grant No. 60978009）, the National Basic Research Program of China （973 Program） （Grant Nos. 2011CBA00200 and 2013CB921804）, and the Program for Changjiang Scholars and Innovative Research Team in University （Grant No. IRT1243）.
