Can the path information be “erased” again?
The disappearance of the interference pattern is connected with the fact that path information can (at least in principle) be read off a photon arriving at the screen. The property “path” was labeled by the property “polarization”.
What happens if this labeling is erased again? Experimentally, this can be achieved by inserting a further polarization filter, set to 45°, after the two beams have been recombined. In the simulation program this is done by activating the “Polarization filter 3” checkbox.
The result is shown in the figure above. An interference pattern appears once more. Path information can no longer be read off a photon striking the screen; it has been erased. This leads to the reappearance of the interference.
The experiment in which the path information is “erased” is also referred to as a quantum eraser.