Figure 8: Action of a lens in a dual-slit setup with different polarization filters ( 𝑅 and 𝐿 ) at the slits—slits 1 and 2 create a two-slit image 1 and 2 , denoted are the focal plane of the lens 𝑓 = 2 . 2 5  m, the image plane of the lens 2 𝑓 . Plotted are the probability density functions at the level of the optical axis ( 𝑦 = 0 ) for photon with 𝜆 = 6 5 0  nm passing through square slits with side of 250 μm separated by distance of 2 mm. There is perfect which-way information due to entanglement of photon polarization with photon path, and there is no interference pattern at the focal plane of the lens.