What is a linear polarized photon? According to Dirac a 'linear' polarized photon is a superposition of left and right rotating photons. Here is a puzzling aspect of this superposition.
There are dichroic materials which can absorb only left photons. What is their effect on this superposition? They would absorb the left state and let the right. It turns out that there are two photons in a 'linear' photon! The mechanical momentum of the dichroic material must be measurable in principle  (like Beth experiment). It would be expected that there is some energy hv absorbed too but it must be in the right photon also. Conservation of energy seems broken? 
If there is no momentum and no energy absorbed in the dichroic the conservation laws are also severely harmed. At least something happens to that photon (linear to right which is easy to show) but nothing happens to the causer of this event (namely to the dichroic). 
I see that there must be wavefunction collapse for the photon and in fact the question boils out to:
Is something physically happening to the machinery causing the collapse? 
 A: There is a misunderstanding about two properties of photons. The first property is the orientation of the electrons electric field component. From a thermal source this component - as well as the magnetic field component - is randomly distributed in space, of course in vacuum always perpendicular to the direction of propagation. A well designed polarizer align approx. 50% of the photons and behind the polarizer their electric fields are oriented in the same direction. But still behind the slits exist a second property. Photons exist with spin orientation in two opposite directions. Suppose, behind the slits the electric field component will be oriented from minus to plus in the horizontal direction from left to right:

Now there are exact two possibilities for the orientation of the magnetic field component: up - down or down - up (don't care about the shift of the amplitudes).
The sequence of the electric and magnetic field components is called the intrinsic spin of a photon. The second possible state is:

Beside this the source could give the photon a torque and the photons field components will rotate. But a photon is a photon and never the superposition of two photons.
A: Conservation of spin would imply that within the dichroic material an electron will change its spin state from +1/2 to -1/2.   Imagine an electron absorbing the photon and gaining energy hv.  Then, relinquishing a photon of the same energy but imparting a left spin state upon it, with the electron's spin state changing accordingly; conserving, energy and spin angular momentum for a single photon interaction.
It's not that easy to break the laws of physics.  Interesting question though, for in order to satisfy those same laws, the net spin of a linearly polarised photon must be zero, even if that zero does consist of +1 + -1.  
