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Conference on Lasers and Electro-Optics

Concentrating partial entanglement of two photons via entanglement swapping

Myung-Joong Hwang, Yoon-Ho Kim

Published Jan 1, 2006• 0 citations
Publisher

Abstract

We report an entanglement concentration scheme in which a photon pair in the |Psi(-)> Bell-state is obtained from two pairs of partially (or non-maximally) . Our scheme is built upon linear optics only and does not require photon-number resolving detectors.
DOI
10.1109/cleo.2006.4629053

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An experimental scheme for concentrating entanglement in partially entangled photon pairs is proposed. In this scheme, two separated parties obtain one maximally entangled photon pair from two previously shared partially entangled photon pairs by local operations and classical communication. A practical realization of the proposed scheme is discussed, which uses imperfect photon detectors and spontaneous parametric down-conversion as a photon source. This scheme also works for purifying a class of mixed states.
We propose practical schemes for concentrating entanglement of a pair of unknown partially entangled Bell states and three-photon W states with cross-Kerr nonlinearity. In these schemes, utilizing local operations and classical communication, two separated parties can obtain one maximally entangled photon pair from two previously shared partially entangled photon pairs, and three separated parties can obtain one maximally entangled three-photon W state and a maximally entangled cluster state from two identical partially entangled three-photon W states with a certain success probability. Finally, we discuss the influence of sources of error and decoherence on the schemes. The proposed setup only employs some linear optical elements and the cross-Kerr medium, which greatly reduces the difficulty of experimental realization. These schemes are feasible with current experimental technology.
With linear optical components to manipulate quantum states of optical fields,the quantum entanglement control and quantum communication can be implemented remotely.By analyzing optical splitter and its use of coherent states,it was found that when the initial state was a direct product of two partially entangled coherent states;another two modes would collapse to a new entangled state using optical splitter and photon-detectors on two modes.Based on this feature,the scheme on entanglement concentration was presented.In this scheme,the two partially entangled coherent states were utilized as the quantum channel,when zero photon and odd photons were detected in two modes separately,and another two modes would collapse to the maximum entangled state,thereby completing the process of the entanglement concentration.It was proved that,no matter how small the initial entanglement is,to distill some maximally entangled states from partially entangled pure states is possible.
The entanglement concentration protocols (ECPs) are presented for distilling the maximally entangled state from a known partially entangled n-photon Bell-class and W state, respectively, only resorting to the linear optical elements and quantum nondemolition detector. Different from the traditional parity check with a single photon as an ancilla, we use linear optical elements for changing the photon paths to realize the concentration. The total success probability of the concentration for n-photon entangled states is calculated. The present protocols only require a partially entangled state and do not need any single auxiliary particle. By iterating the ECP repeatedly, the maximal success probability can be increased. Meanwhile, the present protocols are more suitable for the photon system due to the simple operations.