If we take two pairs of entangled photons (A+B and C+D), and take one from each pair (B and C) and perform a bell-state measurement on them (or another scheme that entangles photons A and D together):(adsbygoogle = window.adsbygoogle || []).push({});

(a) if the two other photons have not had their wave function collapsed, four-photon entanglement is created: http://arxiv.org/abs/quant-ph/0104047

(b) if the two photons had been measured, and then a bell state measurement occured (or similiar), a different result is evident (i.e. not the same result as (a)).

I've seen (b) realised in delayed-choice entanglement swapping, but is there another scheme that would generate different results if measurement had occured before photons A and D became entangled?

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# Is this experiment possible

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