An specialist in quantum information asserted that "entangled photons will never show an interference pattern", but that seems to contradict the response to another question I made here. He asserted that because which-path information is available to Alice (even if for a moment) the interference pattern cannot form because the cross terms never appear.

So if Alice and Bob share many entangled photons with parallel polarization, what will happen to the photons if the simple experiment below is performed by Bob on his photons while Alice will just keep her photons from decohering.

Bob will pass his photons through a double-slit with quarter-wave plates with fast axis at angles $\theta_1=45^o$ and $\theta_2=-45^o$ at each slit. Then it passes through, the eraser, a quarter-wave plate at $\theta_3=0^o$.

Notice that is NOT the typical quantum eraser with entangled photons as seen in this paper A double-slit quantum eraser, the which-path eraser is in Bob's part of the experiment.

If non-entangled light is used in Bob's side of the experiment he will see an interference pattern.

Image to help understanding the experiment:

Simple experiment

So, what is the case?

  1. Bob will always see the interference pattern, independent whether the photons are entangled or not


  1. Bob will never see an interference pattern if photons are entangled?
  • $\begingroup$ "entangled photons with parallel polarization" is not a sufficiently detailed description to specify what state you're talking about. (The question is unanswerable in its current form as a result.) What exactly do you mean by this? $\endgroup$ – Emilio Pisanty Aug 19 at 22:39
  • $\begingroup$ Presumably the OP means "photon pairs with entangled polarizations". $\endgroup$ – Guy Inchbald Aug 20 at 9:51