reply to post by mbkennel
When you quote these things out of context, you tell a half truth. Here's more:
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.
Again, you're getting mixed up with entanglement swapping and the delayed choice aspect of the experiment. Let me break it down:
When the experiment starts. Photons 1&4 that are with Alice and Bob are measured and they don't show any entanglement because photons 1&4 haven't
interacted. So of course photons 1&4 are completely random at this point.
Next photons 2&3 are sent to Victor. Remember, photons 1&2 and 3&4 are entangled. This gets to the entanglement swapping portion of the experiment.
Victor gets photons 2&3 after Alice and Bob have measured photons 1&4. He then makes a measurement on photons 2&3 that determine if entanglement
swapping has or hasn't occurred.
THE ONLY REASON YOU NEED VICTORS RESULTS IS TO CONFIRM THE DELAYED CHOICE PORTION OF THIS EXPERIMENT.
You don't need Victors results to determine if entanglement swapping has occurred on photons 1&4.
In the experiment, they were seeing if Victors results still could effect photons 1&4 after photons 1&4 have been measured. You don't need Victors
results to send information faster than light or to send information to Alice and Bob.
Think about it, it's really simple.
In the delayed choice portion, Alice and Bob will be making a measurement before Victor makes his measurement. When sending information, Alice and Bob
will not measure photons 1&4 until Victor has made his choice to entangle or not to entangle photons 2&3.
Again, you're getting lost in the delayed choice portion of the experiment. Of course Bob and Alice will find complete randomness when they measure
photons 1&4 before Victor chooses to entangle or not to entangle photons 2&3.
WHEN SENDING INFORMATION FASTER THAN LIGHT VICTOR WILL CHOOSE TO SWAP ENTANGLEMENT OR NOT SWAP ENTANGLEMENT BEFORE ALICE AND BOB MEASURE PHOTONS
The article tells you that Alice and Bob can know if entanglement swapping has occurred or hasn't occured by measuring photons 1&4.
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
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
WHEN VICTOR CHOOSES A BELL STATE MEASUREMENT ON PHOTONS 2&3 STRONG CORRELATION ON ALL 3 BASES OCCURS BETWEEN PHOTONS 1&4. WHEN VICTOR CHOOSES A
SEPARABLE STATE MEASUREMENT OR NOT TO SWAP ENTANGLEMENT, CORRELATION OCCURS ON ONE OF THE 3 BASES BETWEEN PHOTONS 1&4!!
To sum it up one more time and this is why you have to read the entire paper instead of looking for parts to quote out of context.
When sending information faster than light Victor chooses to swap or not swap entanglement before Alice and Bob measure photons 1&4. When carrying out
the delayed choice portion of the experiment, Victor measures Photons 2&3 after Alice and Bob measure photons 1&4.