Hello. I'm trying to make a "Mach–Zehnder interferometer", that would show a same-named paradox. In plain words: Two half-silvered mirrors, two full mirrors, the beam is split, then merged together. At the merge point one way the photon is cancelled out, while the other way it is combined. So, we should see only one beam, specifically one parallel to the incoming beam. Furthermore, breaking one of the split beams should produce two beams at the output. That is, this: However, trying to make this in a naive way produced a total lack of anything unusual. Basically, i used a laser diode, two beam splitters and two polished pieces of metal as mirrors. After carefully aligning it all, i got two beams coming out of the combining beam splitter. What it looks like: http://orbides.1gb.ru/img/interfer.jpg The question is: What have i missed or done wrong? Is it a matter of precision, or something is fundamentally wrong?