A question about entanglement swapping

[Heidi]

Happy new year for all the forumers,
My question is about a modification of entanglement swapping:
We use to have two sources of maximally entangled pairs (a and A) and (b and B)
when a is up then A is also up, same thing for b and B
and up and down refer to a measurement along a given direction
After swapping A and B are maximally entangled
The modification: a and A are maximally entangled along a given direction . b and B alson but along another direction
I wonder if there is a possible entanglement (not maximal) between A and B

 

[DrChinese]

1. The modification: a and A are maximally entangled along a given direction . b and B alson but along another direction

2. I wonder if there is a possible entanglement (not maximal) between A and B

1. a and A cannot be polarization entangled in a direction prior to measurement. After measurement of course, they will no longer be entangled.

2. This wasn't your question, but I will pass this along just for fun: sometimes, an entangled source produces 4 photons rather than the usual 2. These 4 photons are entangled, but not maximally so. The 4 as a group are not separable, and as a group obey a conservation rule. A measurement on one of the 4 will leave the remaining 3 entangled, but again not maximally so. A measurement on a second photon will leave the remaining 2 entangled. That remaining pair may be maximally entangled.

 

[Heidi]

At the end of the experiment , when Alice and Bob (who shared pairs of entangled particles) look a the results, when they had chosen a common direction, there was a perfect correlation between the results of Bob and Alice devices. they are maximally entangled.
when the chosen directions slightly differ, there is also correlation but not perfect.
this may be what i was looking for.

 

[r20]

1. a and A cannot be polarization entangled in a direction prior to measurement. After measurement of course, they will no longer be entangled.

2. This wasn't your question, but I will pass this along just for fun: sometimes, an entangled source produces 4 photons rather than the usual 2. These 4 photons are entangled, but not maximally so. The 4 as a group are not separable, and as a group obey a conservation rule. A measurement on one of the 4 will leave the remaining 3 entangled, but again not maximally so. A measurement on a second photon will leave the remaining 2 entangled. That remaining pair may be maximally entangled.

The "for fun" #2 information is interesting. Where can I learn more about that?

 

[DrChinese]

The "for fun" #2 [multi-photon entanglement] information is interesting. Where can I learn more about that?

Here are a few:

Two independent photon pairs versus four-photon entangled states in parametric down conversion
Experimental observation of four-photon entanglement from down-conversion
Four-photon orbital angular momentum entanglement

These papers are fairly technical. The rules on entanglement between N particles can get confusing pretty quick. So no guarantees on the "fun" part.