Practical scheme for entanglement concentration
Zhi Zhao, Jian-Wei Pan, Mingsheng Zhan · Physical Review A · 2001
We present a realistic purification scheme for pure nonmaximally entangled states. In the scheme, two distant parties Alice and Bob first start with two shared but less entangled photon pairs to produce a conditional four-photon Greenberger-Horne-Zeilinger state, and then perform a $45\ifmmode^\circ\else\textdegree\fi{}$ polarization measurement onto one of the two photons at each location such that the remaining two photons are projected onto a maximally entangled state.