Experiment: Mach-Zehnder interferometer

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Objective: Demonstration of “quantum erasure” in an experiment by analogy

Light itself can be described in quantum mechanics by means of wave equations. From this it is possible to derive the spatial distribution of the probability density in the form of the square of the modulus of the wave function. Light is therefore suitable for experiments which demonstrate quantum mechanical phenomena by analogy. Such an analogy experiment demonstrates the so-called quantum eraser effect by setting up a Mach-Zehnder interferometer and observing interference between the split beams on a screen. If two perpendicular polarisers are placed in the paths of the split beams, the interference vanishes since, in quantum mechanical terms, it is possible to determine the path a photon has taken. If a third polarising filter set at an angle of 45° is placed directly in front of the screen, this quantum information is “erased” and the interference can be seen once again.