OK, in the quantum eraser set up, you get a bump because of decoherence in the beam that does not pass through the double slit. In that beams causes the vector states of the left and right slit to be orthogonal. Even if you put the pi/4 POL in that beam, there would be two orthogonal states (the ones that go through and the ones that don't). I thought that what ever you did you'll get two orthogonal states because unitarity assures that orthognoal states will evolve into orthogonal states. And thus us long as time evolution is unitary, you can't get away from the ugly light bump of dechoerent states, as I understand it. However, recently, I heard that there are some non-unitary processes. For example, I heard that photon absorption is non-unitary. I was dazzled at this because, to me that meant that information can be lost, and if I put a simple black body in the other beam, I would get interference! Obviously both information loss and FTL, if possible, are quite groundbreaking things, that can't be that simple to find, so I guess there something wrong with what I am saying. Thank you on before hand!