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In our experiment, the primary events are the polarization measurements of photons 1 and 4 by Alice and
Bob. They keep their data sets for future evaluation. Each of these data sets by itself and their correlations are
completely random and show no structure whatsoever. The other two photons (photons 2 and 3) are delayed
until after Alice and Bob’s measurements, and sent to Victor for measurement. His measurement then decides
the context and determines the interpretation of Alice and Bob’s data
According to Victor’s choice of measurement (i.e. entangled or separable state) and his results (i.e. |Φ+〉23,
|Φ−〉23, or |𝐻𝐻〉23, |𝑉𝑉〉23), Alice and Bob can sort their already recorded data into 4 subsets
In our experiment, the primary events are the polarization measurements of photons 1 and 4 by Alice and Bob. They keep their data sets for future evaluation. Each of these data sets by itself and their correlations are completely random and show no structure whatsoever. The other two photons (photons 2 and 3) are delayed until after Alice and Bob’s measurements, and sent to Victor for measurement. His measurement then decides the context and determines the interpretation of Alice and Bob’s data. In our setup, using two-photon measurement which projects photons 2 and 3 either onto |Φ+〉23 or onto |Φ− 〉23 . This would swap entanglements onto photons 1 and 4. Instead of a Bell measurement, Victor may perform a Bell-state polarization of these photons individually and project photons 2 and 3 either onto |HH〉23 or onto |VV〉23 ,entanglement to photons 1 and 4. Instead of a Bell-state measurement, Victor could also decide to measure the polarization of these photons individually and project photons 2 and 3 either onto HH 23 or onto VV 23 which would result in a well-defined polarization for photons 1 and 4, i.e. a separable state.
According to Victor’s choice of measurement (i.e. entangled or separable state) and his results (i.e. |Φ+ 〉23 ,
|Φ− 〉23 , or |HH〉23 , |VV〉23 ), Alice and Bob can sort their already recorded data into 4 subsets. They can now verify that when Victor projected his photons onto an entangled state (|Φ+ 〉23 or |Φ− 〉23), each of their joint subsets behaves as if it consisted of entangled pairs of distant photons. When Victor projected his photons on a separable state (|HH〉23 or |VV〉23 ) Alice and Bob's joint subsets behave as if they consisted of separable pairs of photons. Whether Alice and Bob's earlier measurement outcomes indicate entanglement of photons 1 and 4 strictly depends on which measurements Victor performs
at a later time on photons 2 and 3.
When Victor performs a Bell state measurement this swaps entanglement which is CONFIRMED by strong correlation between 3 bases for photons 1&4. When this occurs the state fidelity is 0.681+/-0.034 and the entanglement witness value is -0.181+/-0.034 which shows entanglement between photons 1&4.
If Victor chooses a separable state measurement, the state fidelity is 0.421+/-0.029 and the entanglement witness value is 0.078+/-0.029 between photons 1&4.
The other two photons (photons 2 and 3) are delayed until after Alice and Bob’s measurements, and sent to Victor for measurement. His measurement then decides the context and determines the interpretation of Alice and Bob’s data.
"The idea is to create two particle pairs, send one to one computer, the other to another," Zeilinger said."Then if these two photons are entangled, the computers could use them to exchange information."