I Are Expectation Values Measured for Coupled Photons from SPDC?

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Entangled photons are produced through parametric down conversion (SPDC), with ordinary and extraordinary beams having distinct polarizations. The discussion raises a question about the relationship between photons that do not emerge from the intersection of the cone shells but are assigned to each shell. It is noted that if these photons are distinguishable, they cannot be considered entangled, as one will be vertically polarized and the other horizontally polarized. The conversation seeks information on whether expectation values have been measured for such distinguishable photons in Type II SPDC. Understanding these measurements could provide insights into the behavior of non-entangled photons in this context.
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Entangled photons are generated, for example, by parametric down conversion (SPDC). The ordinary photon beam has polarization 0° and the extraordinary photon beam comes with the polarization 90°. Each photon leaves the source in a cone of light. Both cone shells intersect in two beams, which are thus each a mixture of horizontally and vertically polarized photons in equal share.

My question is how are photons related, which do not emerge on the line of intersection of the cone shells but are each clearly assigned to one of the two cone shells.

Does anybody know if this is measured already?
 
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emuc said:
My question is how are photons related, which do not emerge on the line of intersection of the cone shells but are each clearly assigned to one of the two cone shells.
If the photons are distinguishable - as they would be in this case - they will not be entangled. One will be V, the other H. This is for what is called Type II SPDC. Not being entangled, they act independently as to polarization.
 
Do you know about measurements of expectation values for this case?
 

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