Opposite spin of entangled photons

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Discussion Overview

The discussion revolves around the properties of entangled photons, specifically whether they exhibit opposite spin and how this relates to their polarization states. Participants explore the implications of conservation of angular momentum and the distinctions between Type I and Type II entangled photon pairs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that entangled photons should have opposite spin due to conservation of angular momentum, but question how this is verified.
  • One participant notes that Cos(0)^2 = Cos(180)^2, suggesting a potential misunderstanding about the nature of the spins.
  • Another participant clarifies that Type I pairs have the same polarization while Type II pairs have orthogonal (crossed) polarizations, indicating a 90-degree offset rather than 180 degrees.
  • There is a discussion about the implications of Type II entangled photons, where if one photon passes through a polarized lens, the other will not, reinforcing the concept of opposite polarizations.
  • Participants acknowledge the definitions of Type I and Type II arrangements in the context of creating entangled photons, with Type I yielding identical polarizations and Type II yielding opposite polarizations.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of Type I and Type II photon pairs and their polarization characteristics, but there remains some uncertainty regarding the implications of these properties on the concept of spin and the verification of opposite spins in entangled photons.

Contextual Notes

The discussion does not resolve the implications of the mathematical relationships presented and how they relate to the physical properties of entangled photons. There is also a lack of consensus on the verification methods for the claims made about opposite spins.

thenewmans
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Quick question: Do entangled photons have opposite spin? If so, how do we know? I mean I know that they should because of conservation of angular momentum. But Cos(0)^2 = Cos(180)^2. So it looks like they’re the same. Or am I missing something.
 
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thenewmans said:
Quick question: Do entangled photons have opposite spin? If so, how do we know? I mean I know that they should because of conservation of angular momentum. But Cos(0)^2 = Cos(180)^2. So it looks like they’re the same. Or am I missing something.

A couple of points: Type I pairs are same polarization, Type II are orthogonal (crossed). Crossed means they are perpendicular, so they are 90 degrees apart. (You were thinking 180 degrees.)
 
OK so what I think you're saying is that 2 entangled photons are offset by 90 degrees so that if one makes it through a polarized lens then you can be sure the other won't. (Type II?) Is that right?

I don't know the types but I do know that photons are bosons with spin 1. So I guess you mean that they're Type II.
 
thenewmans said:
So I guess you mean that they're Type II.

Type I and Type II are terms for the types of PDC crystal arrangements that are most often used for creating entangled photons. With a Type I arrangement (which is actually 2 crystal arranged perpendicularly), you get identical polarizations. With Type II, you get crossed (opposite) polarizations.
 
DrChinese said:
Type I and Type II are terms for the types of PDC crystal arrangements that are most often used for creating entangled photons. With a Type I arrangement (which is actually 2 crystal arranged perpendicularly), you get identical polarizations. With Type II, you get crossed (opposite) polarizations.

Very cool! Thank you.
 

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