How do you explain this? Will the photon go through the second filter? Yes, No or ?????
What is detected on the far side of a filter is either a photon or no photon. However, whether it gets through or not is calculated using components of a wave. This is another example of wave-particle duality.
The photon’s state of polarization is disturbed by a filter. This is also an example of measurement-disturbance.
If the photon gets through a vertical polarizer, then we are certain it will go through a vertical filter but not a horizontal one. This is also an example of Heisenberg’s Uncertainty Principle.
However, we are uncertain about any other basis. We are reduced to probabilities. It will have a 50:50 chance of going through a filter at 45 0.
Classical Interference A laser beam is aimed at a pin. Sketch what will you see up close and far away.
Quantum Double-Slit Interference Does a photon go through one slit, neither or both? If the light is really, really low intensity, we have another example of wave-particle duality and measurement-disturbance.
What happens with electrons? This was tested in Tubingen in 2006. top view metal plates
Electrons that induced a current in one of the metal plates, showed which slit they went through. side view metal plates
Only electrons near the metal plates were detected. metal plates
Electrons far from the metal plates were not detected. Electrons near the metal plates were detected.
If you are uncertain, the two possibilities can interfere. If you are certain which path it took, there will be no interference pattern.
What will you see if you put horizontal and vertical polarizers on either side of a double slit?
The polarizers allow us to be certain as to which slit the photons went through, so the interference pattern disappears. What will happen if you add a third polarizer after the slits?
If the polarizer is at 45 o, the pattern returns. Why? After a photon passes through a 45 o filter, we are uncertain whether it was vertical or horizontal. We don’t know which way it went.
The polarizer is acting as a quantum eraser. It erases our knowledge of which way the photon went.
So, which way does the photon go? If we are certain which way it went, it acts like a particle. There is no interference pattern.
So, which way does the photon go? Only if we are uncertain of its path, does acts like a wave and make an interference pattern. We can’t be certain.
Measurement produces certainty of a photon’s polarization in one basis and destroys it in all others. Diffraction is a result of the uncertainty in momentum caused by a slit measuring position. Certainty of which slit a photon goes through destroys the interference pattern.