Non-unitary process? Doesn't that mean FTL?

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guillefix
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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!
 

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No, there is nothing wrong with what you are saying. The idea of non-unitary processes is indeed a very interesting one and could potentially have major implications for quantum mechanics. In fact, many researchers have been exploring the possibility of non-unitary processes in quantum systems, and have found that they can indeed exist in certain scenarios. For example, it has been shown that a photon absorption process can be non-unitary, as can certain forms of decoherence. In these cases, information can indeed be lost, and this can lead to interference effects in the beam that passes through the double slit. However, it is important to note that non-unitary processes are not necessarily easy to find or to exploit in order to create interference. In fact, most theoretical studies of non-unitary processes are still in their infancy, and so far no conclusive evidence has been found that suggests they can be used to create interference in the way you suggest. As such, it is still too early to say for sure whether non-unitary processes can help to explain the quantum eraser phenomenon.